Category: ADU

An accessory dwelling unit is a second, complete home on a lot that already has a house on it. California law defines it as a unit with permanent provisions for living, sleeping, eating, cooking and sanitation — and that word “cooking” is the whole test. A structure with a bedroom and a bathroom but no kitchen is not an ADU. Add a kitchen and it is. Everything else people argue about, including whether to call it a granny flat, a casita or a mother-in-law suite, is vocabulary rather than law. Green Design and Build is a licensed general contractor (CSLB #1110975) based in Van Nuys that designs, permits and builds ADUs across Los Angeles County, Orange County, Ventura County, western Riverside County and western San Bernardino County.

We are led by Dekel Sofer, who has more than 16 years of hands-on construction experience; the company has completed hundreds of projects and holds a 4.7-star rating across 146 reviews on Yelp. The state rules below apply everywhere in California. The Los Angeles specifics are called out separately, because the local half of this varies by city.

The legal definition, and the one word that decides it

Under Government Code section 66313, an accessory dwelling unit is an attached or detached residential dwelling unit that provides complete independent living facilities for one or more people, on a lot with an existing or proposed primary residence. It must include permanent provisions for five things: living, sleeping, eating, cooking and sanitation. An efficiency unit and a manufactured home both count.

Four of those five are easy. The fifth is the line everything turns on. The City of Los Angeles makes it even blunter in its own zoning code, which defines a dwelling unit as a group of two or more rooms, one of which is a kitchen, designed for occupancy by one family. No kitchen, no dwelling unit. That single distinction decides whether your project is an ADU with state protection behind it, or an accessory building with none.

Every other name for an ADU

Most people searching for this do not use the letters A-D-U. They use a word they grew up with. None of the terms below is defined anywhere in California statute or in the Los Angeles Municipal Code; the state’s own housing department acknowledges as much, noting that ADUs “have been known by many names: granny flats, in-law units, backyard cottages, secondary units and more.”

What people call it	Legal status in California	What it usually means in practice
Granny flat	Colloquial	Any ADU, usually detached, often built for a parent
Mother-in-law suite / in-law suite	Colloquial	Usually an attached ADU or a junior ADU inside the house
Casita	Colloquial	A small detached unit, often Spanish or Mediterranean in style
Backyard cottage	Colloquial	A detached ADU
Secondary suite / secondary unit	Colloquial	An ADU. “Second unit” was California’s old statutory term
Carriage house	Colloquial	An ADU above or inside a detached garage
Guest house	Not an ADU	No kitchen. In Los Angeles this is a separate zoning category with its own rules — see below
Junior ADU (JADU)	Defined in statute	Up to 500 sq ft, inside the walls of the existing house
Movable tiny house	Defined by the City of Los Angeles	A DMV-registered unit on wheels, 150 to 430 sq ft

The practical consequence is simple: if you ask a building department for a granny flat, nobody will know what standard to apply to you. Ask for an accessory dwelling unit and a specific, generous body of state law attaches to your application.

The four kinds of ADU

Type	Where it goes	Worth knowing
Detached, new construction	A new structure in the yard	Cities must allow at least 800 sq ft with four-foot side and rear setbacks
Attached	Built onto the existing house	Shares a wall; height is tied to the main house
Conversion	Inside existing space — a garage, a basement, part of the house	No new setback required, and up to 150 sq ft of expansion is allowed purely for entry and exit
Junior ADU (JADU)	Within the walls of the single-family house, including an attached garage	500 sq ft maximum, and its own rulebook

Our guides compare a detached ADU against a garage conversion and weigh an ADU against a room addition if you are deciding between them.

What a junior ADU actually is

A JADU is no more than 500 square feet of interior livable space, contained entirely within the walls of a single-family residence. It is the cheapest way into an ADU because you are not building a structure, and it is the most misunderstood. The rules:

• One JADU per residential lot.
• It needs its own exterior entrance, separate from the main entrance to the house.
• It needs an efficiency kitchen: a cooking facility with appliances, plus a food preparation counter and storage cabinets sized reasonably for the unit. Notably, the state housing department has said cities may not dictate counter or cabinet sizes, specific electrical or gas connections, or appliance types.
• Sanitation can be shared with the house or separate.
• A deed restriction is recorded, prohibiting sale of the JADU separately from the house.
• Rentals must be longer than 30 days, so no short-term letting.
• Owner-occupancy changed on 1 January 2026. Under AB 1154, it is now required only where the JADU shares sanitation facilities with the house. Give the JADU its own bathroom and the owner-occupancy requirement falls away. Local ordinances written before 2026 may still show the old blanket rule; state law governs.

Our junior ADU cost guide covers what one costs to build.

How small can an ADU be?

Smaller than most people expect. California’s Health and Safety Code allows an efficiency unit with a minimum floor area of 150 square feet for occupancy by up to two people, and state ADU law separately forbids a city from setting a minimum ADU size that would prohibit an efficiency unit. So a 150-square-foot ADU is legal in principle anywhere in California.

You may see 190 square feet quoted as the minimum. There is no statute or code section behind that number and we can find no official source for it; it appears to be an error that has propagated across contractor websites. The figure that does exist alongside 150 is 220 square feet, which comes from the Building Code’s efficiency dwelling unit provisions, and the state has specifically rejected attempts to use it as an ADU minimum.

Separately, the Residential Code sets habitability floors that apply to any room: habitable rooms other than kitchens must be at least 70 square feet and at least 7 feet in any horizontal direction, with ceilings at least 7 feet high, or 6 feet 8 inches in a bathroom or laundry.

How many can you have on one lot?

On a single-family lot, three, as a floor rather than a ceiling. State law requires cities to ministerially approve a combination of: one ADU created within existing space, one junior ADU, and one newly constructed detached ADU. That is three additional units alongside the primary residence, and the state housing department’s own handbook states it in those terms. A city may allow more under its own ordinance; it may not allow fewer.

ADUs also do not count against your lot’s allowable density. Government Code section 66319 says an ADU is an accessory use that “shall not be considered to exceed the allowable density for the lot.” Do not over-read that, though: ADUs are still counted as housing units in the state’s regional housing reporting. It means your zoning does not block them, not that they are invisible.

A guest house is not an ADU, and in Los Angeles it has its own rules

This is where most published advice goes wrong, and it matters, because “can I just build a guest house instead” is one of the most common questions we get.

First, the Los Angeles Municipal Code does define “Guest House” — but not the way you think. In the LAMC a Guest House is a dwelling containing not more than five guest rooms or suites of rooms with no kitchen facilities. That is a lodging definition. The backyard building homeowners mean is a different defined term: Accessory Living Quarters, which the code describes as an accessory building used solely as the temporary dwelling of guests of the occupants, having no kitchen facilities and not rented or otherwise used as a separate dwelling unit.

You can still build one in Los Angeles. The catch is in the R1 zone rules: accessory living quarters may not be located on a lot smaller than 10,000 square feet. Most Valley and South Bay lots are well under that. And unlike an ADU, an accessory living quarters gets no state protection at all — no guaranteed four-foot setbacks, no ministerial approval, no minimum size the city must allow. You are entirely in the hands of local zoning.

What counts as a “kitchen” for this purpose is more expansive than a stove. The City’s zoning interpretation manual has historically treated a natural gas outlet, a 220-volt outlet, a double sink, a bar sink over one square foot, a hot water line to a bar sink, a refrigerator over 10 cubic feet, a garbage disposal, a dishwasher or the space for one, any device designed for cooking or heating food, and more than 10 square feet of counter as kitchen facilities. That is interpretive guidance rather than code text, and it dates from an older edition of the manual, so confirm the current position with the department — but it tells you how carefully this line is policed.

And if you build a kitchen-less guest room and quietly add a kitchen later? It stops meeting the accessory living quarters definition and becomes an unpermitted dwelling unit. That is a code enforcement problem, not an upgrade. The lawful route is to permit it as an ADU from the start — which, given the state protections an ADU carries and the 10,000-square-foot lot rule a guest house does not escape, is usually the easier path anyway.

Movable tiny houses

The City of Los Angeles recognises a category most cities do not. A Movable Tiny House is registered with the DMV, meets ANSI 119.5 or NFPA 1192 standards, cannot move under its own power, and measures between 150 and 430 square feet. In Los Angeles it can serve as an ADU. Treat this as a City of Los Angeles answer only: other jurisdictions handle tiny houses on wheels very differently and many do not accept them as ADUs at all.

What if there is already a unit back there?

Two different pathways, and they get blurred constantly.

A lawfully permitted structure with no kitchen — a guest room, a rec room, a garage — converts under the state’s conversion provision. The city must approve it ministerially, and you are allowed up to 150 square feet of expansion beyond the existing footprint purely to create entry and exit. The work is adding a compliant kitchen and bringing the building up to habitability standards.

An unpermitted unit someone has been living in is a different statute. Government Code section 66311.7 (which you may see cited by its old number, 66332) lets you legalise a unit built before 1 January 2020. The city cannot deny the permit for building-standard violations or for failing to meet the local ADU ordinance, and cannot charge impact fees. Los Angeles implements it through a documented process with a health-and-safety checklist, and the unit may comply either with current codes or with the codes in effect when it was built. You will need to evidence the construction date — utility bills, leases, contractor receipts.

The kitchen, in practice

This Los Angeles project is a garage conversion: the same footprint, a new kitchen with full appliances, a bathroom, and French doors where the garage door used to be. Once that kitchen went in, the building stopped being a garage and became a dwelling unit, with everything that follows from it. The full sequence is on the garage-to-ADU conversion project page.

How common are ADUs now?

Common enough to have changed what California builds. According to the state housing department’s March 2026 ADU handbook, ADUs permitted annually across California grew from 1,336 in 2016 to 30,354 in 2024, and in 2024 they made up more than 26.6 percent of all homes permitted statewide. Those are permits rather than finished buildings, so treat them as a measure of intent as much as output — but better than one in four homes permitted in California being an ADU is a genuine shift, and it is why the law keeps moving in their favour.

What it costs and how long it takes

Covered properly in their own guides rather than summarised badly here: what an ADU costs to build, what a garage conversion costs, how long an ADU takes, and how homeowners pay for them. If quotes you have received vary wildly, there are specific reasons for that.

For what your particular lot allows, we publish ADU rules by city across Southern California, an ADU rules calculator, and a guide to the LADBS standard plan program, which is the shortcut most homeowners miss.

Where we build ADUs

We build ADUs from our Van Nuys office across the San Fernando Valley, the rest of Los Angeles County, Orange County, Ventura County, western Riverside County and western San Bernardino County. The mix changes by area: garage conversions dominate in the older Valley neighbourhoods where detached garages sit at the back of the lot, detached new construction is more common on the wider lots of the Inland Empire and outer Orange County, and junior ADUs make the most sense in larger houses where a wing can be separated off. See our ADU construction service and all of our service areas.

ADU FAQs

What is an ADU?

An accessory dwelling unit is a second, self-contained home on a lot with an existing or proposed primary residence. California law requires it to have permanent provisions for living, sleeping, eating, cooking and sanitation. In practice the kitchen is the defining feature: a structure with a bedroom and bathroom but no kitchen is not an ADU. It can be detached, attached to the house, or created inside existing space such as a garage.

Is a granny flat the same as an ADU?

Yes. “Granny flat” is a colloquial term with no definition in California statute or in the Los Angeles Municipal Code. So are mother-in-law suite, in-law suite, casita, backyard cottage, secondary suite and carriage house. The state housing department itself notes ADUs have been known by many names. Use “accessory dwelling unit” when you apply for a permit, because that is the term the law attaches to.

What is the difference between an ADU and a guest house?

A kitchen. An ADU has one; a guest house does not, and without one it is not a dwelling unit. In Los Angeles the backyard version is formally called accessory living quarters, and it may not be built on a lot smaller than 10,000 square feet in the R1 zone. A guest house also gets none of the state protections an ADU receives, such as guaranteed four-foot setbacks and ministerial approval, so on most lots the ADU route is both easier and more useful.

What is a junior ADU?

A JADU is up to 500 square feet of interior livable space created entirely within the walls of a single-family house, including an attached garage. It needs its own exterior entrance and an efficiency kitchen with a cooking facility, appliances, a food preparation counter and storage. Sanitation may be shared or separate, and a deed restriction is recorded against the property. Since 1 January 2026, owner-occupancy is required only where the JADU shares a bathroom with the house.

How many ADUs can I build on my property?

On a single-family lot, state law requires cities to allow a combination of one ADU created within existing space, one junior ADU, and one newly built detached ADU — three additional units alongside the house. That is a minimum, not a maximum; a city may permit more. ADUs also do not count toward your lot’s allowable density.

How small can an ADU be?

California allows an efficiency unit with a minimum floor area of 150 square feet for up to two occupants, and a city may not set an ADU minimum size that would prohibit one. Habitability rules still apply: habitable rooms other than kitchens must be at least 70 square feet and 7 feet in any horizontal direction, with 7-foot ceilings. The 190-square-foot minimum widely quoted online has no statutory basis that we can find.

Can I rent out an ADU?

Yes, for terms longer than 30 days. Cities may require, and in practice nearly always do require, a minimum 30-day rental term, which rules out short-term letting. A JADU carries the same 30-day floor. An ADU generally cannot be sold separately from the main house, though a small number of California cities have opted into a condominium pathway that allows it.

Can I legalise an unpermitted unit in my backyard?

Often, yes, if it was built before 1 January 2020. Government Code section 66311.7 requires cities to permit qualifying unpermitted ADUs and junior ADUs without denying them for building-standard violations or for failing the local ADU ordinance, and without charging impact fees. The unit may comply with either current codes or the codes in effect when it was built, and a health-and-safety review applies. You will need documentation of the construction date.

Find out what your lot actually allows

We will look at the lot, the setbacks, the existing structures and your city’s current ordinance, and tell you which of the three routes — conversion, junior ADU or new detached unit — makes sense on your property before anyone draws anything. The site visit takes about two hours, the written proposal follows within 48 hours, and both are free. We reply within one business day.

A junior accessory dwelling unit (JADU) is a unit of no more than 500 square feet of interior livable space created entirely inside an existing or proposed single-family house, including an attached garage, with its own entrance and an efficiency kitchen; it may share a bathroom with the main house. Because a JADU reuses the roof, walls and floor you already have, it is usually the least expensive legal way to add a second unit, and it pays no development impact fees. Green Design and Build is a licensed, bonded and insured general contractor (CSLB #1110975) based in Van Nuys, building ADUs, JADUs and garage conversions for homeowners across Los Angeles County, Orange County, Ventura County, western Riverside County and western San Bernardino County (Ontario, Rancho Cucamonga and neighbouring cities).

We are led by Dekel Sofer; the company has completed hundreds of projects and holds a 4.7-star rating across 146 reviews on Yelp.

What a JADU is, in the words of the law

The rules for junior ADUs sit in California Government Code section 66333, and every city in our service area, including the City of Los Angeles, has to allow them. Verified against the Department of Housing and Community Development’s ADU Handbook (March 2026 edition), the definition has six parts:

1. Size. No more than 500 square feet. Since January 1, 2026 the statute measures “interior livable space,” so wall thickness does not count against you.
2. Location. Contained entirely within the single-family residence. An attached garage counts as part of the house, so converting an attached two-car garage into a JADU is the most common version we build. A detached garage cannot be a JADU; it becomes a garage conversion ADU instead.
3. Kitchen. An efficiency kitchen, which the statute defines as “a cooking facility with appliances, a food preparation counter, and storage cabinets that are of reasonable size in relation to the size of the JADU.” A city cannot demand a specific counter length, a 240-volt range circuit or a full-size stove.
4. Bathroom. A JADU “may include separate sanitation facilities or may share sanitation facilities with the existing structure.” If it shares, it must have its own exterior entrance and an interior door into the main living area.
5. Owner occupancy. Since January 1, 2026 (AB 1154), the owner must live in either the house or the JADU only when the JADU shares a bathroom with the house. Give the JADU its own bathroom and no owner-occupancy requirement applies. The requirement never applies when the owner is a government agency, land trust or housing organization.
6. Deed restriction. The city may require a recorded deed restriction that does two things and only two: prohibits selling the JADU separately from the house, and holds the unit to the size and attributes state law allows. The City of Los Angeles records it before the permit issues.

Two more rules matter. Only one JADU is allowed per lot. And no city may require parking for a JADU, even when it replaces an attached garage.

JADU plus ADU: the two-unit lot

The reason JADUs are worth knowing about is Government Code section 66323. On a single-family lot, a city must ministerially approve one JADU (or one ADU converted from existing space) together with one new detached ADU of up to 800 square feet with four-foot side and rear setbacks. That is how a standard 1950s Valley ranch house on a 6,000-square-foot lot ends up with three legal units: the house, a JADU in the attached garage, and a detached unit in the back yard. The detached unit is where most of the money and the rental value sit; the JADU is the inexpensive second one. Our ADU rules hub and the ADU rules calculator show the minimums your city has to allow for both.

How much does a JADU cost in Los Angeles?

A JADU in Los Angeles typically costs $60,000 to $150,000. That figure and every other on this page are typical Los Angeles budgeting estimates, not a price list or a quote. Your project can come in lower or higher depending on the house, the scope and the finishes; the only real number is a written proposal after a site visit.

The ceiling to compare against is the published range for a garage conversion ADU, $100,000 to $200,000, because a JADU built in an attached garage is the same shell with less plumbing: it can share the bathroom, and its kitchen is a cooking counter rather than a full kitchen with a range hood ducted through the roof. A JADU carved out of a bedroom wing with a new exterior door and no bathroom of its own sits at the low end; a garage JADU with its own bathroom, a new slab section for the drain, and a panel upgrade sits at the high end and overlaps the garage-conversion range.

Item	What it involves	What moves it
Structure and envelope	Insulating and sheathing garage walls, replacing the garage door with a framed wall and entry, new windows for egress and light	A garage slab with no vapor barrier has to be sealed or overlaid; sloped garage slabs need leveling
Efficiency kitchen	Counter, cabinets, sink, plug-in or small built-in appliances; a 20-amp circuit or two	A full range with a hood ducted outside turns it into a full kitchen and adds gas or 240-volt work
Bathroom	Optional; sharing the house bathroom removes the largest plumbing cost	Cutting the slab for a new drain, and where the sewer lateral runs
Electrical	New circuits, lighting to Title 24, smoke and carbon monoxide alarms	Many 1950s to 1970s houses need a 200-amp panel first; the published range for that upgrade is $6,000 to $8,000
Heating and cooling	A ductless mini-split heat pump is the usual answer	Panel capacity and the outdoor unit’s location
Fire separation	Rated drywall and a self-closing door between the JADU and the house where the code requires it	Garage-to-house walls usually already have the rated layer; ceilings often do not
Permits and deed restriction	LADBS or city plan check, the recorded covenant, inspections	No impact fees; connection fees are not charged for a unit inside existing space

The published ranges for other ADU types are in our guide to how much it costs to build an ADU on your property, and the garage figures are broken down in our garage conversion cost guide.

JADU vs ADU vs garage conversion

	Junior ADU	Garage conversion ADU	Detached ADU
Maximum size	500 sq ft interior livable space	Existing garage footprint (plus up to 150 sq ft for entry and egress)	800 sq ft guaranteed by state law; up to 1,200 sq ft in the City of Los Angeles and many other cities
Where	Inside the house or attached garage	Attached or detached garage	New building in the yard, 4 ft side and rear setbacks
Kitchen	Efficiency kitchen	Full kitchen	Full kitchen
Bathroom	Own or shared with the house	Own	Own
Owner must live on site	Only if the bathroom is shared	No	No
Deed restriction	Yes, in most cities	No	No
Impact fees	None	None (750 sq ft or less)	None at 750 sq ft or less; proportionate above
Replacement parking	None required	None required	None required
Fire sprinklers	Not required if the house has none	Not required if the house has none	Not required if the house has none
Solar	Not required	Not required	Required on new detached units in the City of Los Angeles
Can be combined with	One detached ADU up to 800 sq ft	One JADU	One JADU or one conversion ADU
Rental term	Longer than 30 days	Longer than 30 days	Longer than 30 days
Typical Los Angeles budgeting range	$60,000–$150,000	$100,000–$200,000	$180,000–$450,000+ by size

When a JADU beats a full ADU

A JADU is the right unit when the budget is the constraint, when the yard is not there, or when the second unit is for family rather than rent. It makes sense for a parent or an adult child who will share the house’s bathroom without friction, for a lot where a detached unit would eat the only outdoor space, and for a homeowner who wants a second permitted unit in months rather than a year. It is also the right first step on a lot that will eventually get a detached ADU too, because the JADU approval does not use up the detached-unit entitlement.

A full ADU is the better answer when rental income is the goal, because a 500-square-foot unit that shares a bathroom and has a hot plate rents for far less than a self-contained unit with its own kitchen and bath; when the only convertible space is a detached garage, which can never be a JADU; and when you do not want a deed restriction or an owner-occupancy condition on title. Our guides to detached ADU vs garage conversion and ADU vs room addition cover the other two decisions on the same lot.

Permits and the 60-day clock

A JADU is a ministerial permit, the same as an ADU. In the City of Los Angeles, including Van Nuys, Sherman Oaks, Encino, Studio City, Woodland Hills, Northridge and North Hollywood, the plans go to LADBS; Burbank, Glendale, Pasadena, Santa Clarita, every Orange County city and the western Riverside and San Bernardino County cities each run their own building divisions under the same state law. The agency has 15 business days to tell you whether the application is complete and then 60 days to approve or deny it. The deed restriction is recorded with the county before the permit issues, and the inspections are the ordinary building, electrical, plumbing and mechanical inspections plus the final.

Inside the house the code issues are practical rather than legal: a bedroom used as a JADU still needs an egress window, the wall and ceiling between an attached garage JADU and the house need the rated drywall and the self-closing door the residential code requires for a garage, and every sleeping room gets interconnected smoke alarms. None of it is hard; all of it should be on the drawings before plan check rather than discovered by the inspector.

How long does a JADU take?

A JADU is the fastest legal second unit because there is no foundation, no roof and usually no utility trenching. Design and drawings take a few weeks, plan check runs inside the statutory 60 days when the submittal is complete, and construction on an attached-garage JADU is measured in weeks rather than months: framing the door opening, rough electrical and any plumbing, insulation, drywall, the kitchen counter, flooring and finish. Six months to a year is the published range for an ADU project overall; a JADU sits at the short end of it, and our how long does an ADU take guide breaks the phases down.

A real garage that became a unit

Our garage-to-ADU conversion in Los Angeles, finished in 2025, shows what the fuller version of this work looks like: a detached two-car garage of about 500 square feet by the pool, with the roof structure rebuilt, new framing and sheathing, new windows and French doors where the garage door had been, stucco to match the tile roof, a full kitchen with an island, a tiled bathroom with a glass shower and wood-look flooring throughout, now a long-term rental. Because the garage was detached it had to be a full ADU rather than a JADU, with its own bathroom and a complete kitchen. A JADU in an attached garage keeps most of that scope and drops the parts that cost the most: the second bathroom’s plumbing and the full kitchen.

The other lesson comes from why ADU quotes vary so much between contractors: a garage conversion estimated at $85,000 to $95,000 that finished near $130,000 after the slab turned out to have no moisture barrier, the 100-amp panel had to become 200 amps, and a camera found root damage in the sewer line. Every one of those applies to an attached-garage JADU too, which is why our site walk starts with the slab, the panel and the sewer.

Where we build JADUs

We build JADUs and ADUs from our Van Nuys office across the San Fernando Valley and the rest of Los Angeles County, where the attached-garage ranch house is the natural JADU candidate; in Orange County, where master-planned communities add HOA review that state law limits but does not remove; in Ventura County; and in western Riverside County and western San Bernardino County, where newer slab-on-grade houses with three-car garages leave room for both a JADU and parking. See every city we serve on our service areas page, and the full picture of what we build on our ADU page and garage conversion page.

Junior ADU FAQs

How much does a junior ADU cost in Los Angeles?

A junior ADU in Los Angeles typically costs $60,000 to $150,000, a typical Los Angeles budgeting range and not a quote; a garage conversion ADU, the closest comparison, runs $100,000 to $200,000 in our published ranges. A JADU that shares the house bathroom and uses a plug-in efficiency kitchen sits at the low end; one with its own bathroom, a slab cut for a new drain and a panel upgrade sits at the high end. These are estimates, not a price list, and the only real number is a written proposal after a site visit.

What is the difference between a JADU and an ADU?

A JADU is limited to 500 square feet of interior livable space, must be inside the existing house or attached garage, needs only an efficiency kitchen, may share a bathroom with the house, and carries a deed restriction and, if the bathroom is shared, an owner-occupancy requirement. An ADU is a fully independent unit with its own kitchen and bathroom, can be detached or converted from a detached garage, can be larger, and has no owner-occupancy condition.

Do I have to live on the property if I build a JADU?

Only if the JADU shares a bathroom with the main house. Since January 1, 2026, California Government Code section 66333 lets a city require owner occupancy of a junior ADU only when the unit shares sanitation facilities with the house; a JADU with its own bathroom carries no owner-occupancy requirement. Some cities still record a covenant on every JADU, so ask before you file.

Can I have a JADU and a detached ADU on the same lot?

Yes. Government Code section 66323 requires cities to approve, on a single-family lot, one junior ADU or one ADU converted from existing space together with one new detached ADU of up to 800 square feet with four-foot side and rear setbacks. A JADU in the attached garage and a detached unit in the back yard is the most common two-unit layout we build in the San Fernando Valley.

Does a JADU need its own kitchen and bathroom?

A JADU needs an efficiency kitchen, which state law defines as a cooking facility with appliances, a food preparation counter and storage cabinets of a reasonable size for the unit; it does not need a full range or hood. It does not need its own bathroom and may share the house’s, in which case it must have a separate exterior entrance and an interior door to the main living area.

Can I convert my detached garage into a JADU?

No. A junior ADU must be contained entirely within the single-family residence, and an attached garage counts as part of the house but a detached garage does not. A detached garage becomes a garage conversion ADU instead, with a full kitchen and its own bathroom, which is a larger scope with a published Los Angeles range of $100,000 to $200,000.

Find out whether your garage should be a JADU or an ADU

Send us your address and a photo of the garage or the room you have in mind. We will walk the lot, check the slab, the panel and the sewer, tell you which unit the law and the house allow, and give you a written, itemized estimate. The site visit and the estimate are free.

A garage conversion ADU turns the slab, walls and roof you already have into a legal dwelling and typically costs $100,000 to $200,000 in Los Angeles; a detached ADU is a new building in the yard, costs $180,000 to $260,000 for about 500 square feet and $300,000 to $450,000 or more for about 1,000 square feet, and gives you a unit whose size, ceiling height, layout and position you choose. Green Design and Build is a licensed general contractor (CSLB #1110975) based in Van Nuys that builds both for homeowners across Los Angeles County, Orange County, Ventura County, western Riverside County and western San Bernardino County (Ontario, Rancho Cucamonga and neighbouring cities). The conversion wins on cost and speed when the garage is sound and where you want the unit; the detached ADU wins when the garage is the wrong size, height or place, or when you want to keep the parking. These are typical Los Angeles budgeting estimates, not a price list or a quote, and your project can come in lower or higher.

We are led by Dekel Sofer. We hold a 4.7-star rating across 146 Yelp reviews and have completed hundreds of projects across all five counties. Our garage conversion and ADU pages describe each service; this guide is the comparison.

Garage conversion vs. detached ADU at a glance

	Garage conversion ADU	Detached ADU
What you get	The existing garage footprint (about 400 sq ft for a two-car garage), plus up to 150 sq ft of expansion for entry and egress under state law	A new unit of the size you choose: state law guarantees 800 sq ft, and the City of Los Angeles allows up to 1,200 sq ft where the lot’s standards permit
Typical Los Angeles budgeting estimate	$100,000–$200,000	About 500 sq ft $180,000–$260,000; 700–800 sq ft $225,000–$350,000; about 1,000 sq ft $300,000–$450,000+; $300–$450 per sq ft all-in
Setbacks	None required for a conversion within the existing footprint (or a rebuild to the same dimensions in the same location)	4 ft from side and rear property lines
Height	The garage’s existing height; ceilings must be at least 7 ft	At least 16 ft, or 18 ft within half a mile walking distance of a major transit stop; two stories where the city allows
Parking	The city cannot require the lost garage parking to be replaced	No parking can be required within half a mile of transit; otherwise at most one space
Fire sprinklers	Not required if the main house has none	Same rule
Solar	Not required for a conversion	New detached ADUs must have solar panels under the state energy code
LADBS standard plans	Not applicable; conversions go through regular plan check with their own drawings	Available for detached units in the City of Los Angeles, which limits plan check to site-specific review
Utility connection	A city or utility cannot require a new or separate connection for an ADU within existing space; shares the house’s water, sewer and panel	May be charged a connection fee proportionate to the unit; usually still fed from the house’s panel after a 200-amp upgrade
Timeline	Shorter end of six months to a year; construction about three to five months	Longer end of six months to a year
What you lose	Covered parking and storage	Yard space; the garage stays
What you cannot change	Slab elevation, ceiling height, footprint position and the original footings	Nothing; it is designed from scratch

These are typical Los Angeles budgeting estimates, not a price list or a quote. Your project can come in lower or higher depending on the house, the scope and the finishes; the only real number is a written proposal after a site visit. The figures are the ones on our homepage and on our garage conversion cost guide and ADU cost guide.

Cost: the garage is a head start, not a discount

A two-car garage conversion at $100,000 to $200,000 against a 500-square-foot detached ADU at $180,000 to $260,000 looks like a clear win for the conversion, and on a sound garage it is. The savings are specific: no foundation, no framing, no roof, no solar array. What you still pay for is everything that makes a garage a home, and a 400-square-foot ADU contains the two most expensive rooms in any house, a kitchen and a full bathroom. A $100,000 to $150,000 conversion of a 400-square-foot garage works out to roughly $250 to $375 per square foot, below the $300 to $450 we publish for new construction; but the ranges overlap, because a detached garage at the back of a deep Valley lot with a cracked slab, a 100-amp panel and a clay sewer lateral can cost as much as a small new unit. What moves either number is the same short list: slab or foundation, the sewer run and the lateral’s condition, the 200-amp service upgrade most 1950s to 1970s houses need, the envelope, and the kitchen and bathroom, which cost the same on both routes. Our garage conversion cost guide itemizes each.

Two real projects, one from each side

The conversion that rose 40 percent. In why ADU quotes vary so much between contractors, a homeowner converting a detached two-car garage of roughly 400 square feet into a one-bedroom ADU with a kitchen, bathroom and laundry started with an estimate of $85,000 to $95,000. Three discoveries moved it to about $130,000: the slab had no proper moisture barrier and needed preparation and concrete work; the home’s original 100-amp panel had to become 200 amps; and a camera inspection found root intrusion and bellying in the sewer, so a section had to be replaced before the new fixtures could connect. None of that was a luxury; each was a condition the garage already had.

The detached unit that went from $180,000 to $265,000. In our ADU cost guide, homeowners who had already removed an old, deteriorated garage planned a roughly 600-square-foot one-bedroom detached ADU on a budget of about $180,000; it finished near $265,000 after a $14,000 clay sewer reroute under the new foundation, a $6,000 to $8,000 panel upgrade with about three weeks of utility delay, and about $30,000 of finish upgrades chosen after framing. It is also the third option this guide keeps coming back to: when the garage is too far gone to convert, demolish it and build new on the same spot.

A finished conversion. Our garage-to-ADU conversion in Los Angeles, completed in 2025, started as a plain stucco box of about 500 square feet with one wide door opening and a single small window and became a self-contained rental with a rebuilt roof structure, new framing and sheathing, new windows and French doors, matched stucco, a full kitchen with an island and a full bathroom with a tiled shower. Notice that the roof structure was rebuilt, which is common once an old garage roof is asked to carry insulation, drywall and a ceiling.

The rules: where each one is allowed

California’s ADU statute lives in Government Code sections 66310 to 66342, and the rules below are verified against it and against LADBS; sources are at the end.

Conversions: no setback, no replacement parking, no separate connection

A garage converted to an ADU within its existing footprint needs no setback; section 66314(d)(7) says none shall be required for “an existing living area or accessory structure or a structure constructed in the same location and to the same dimensions as an existing structure” that is converted, and section 66323(a)(1) lets the unit expand up to 150 square feet for entry and exit. A garage one foot off the rear property line can become an ADU where a new building could not, provided the wall assembly handles fire separation. When a garage, carport or covered parking is converted or demolished for an ADU, section 66314(d)(11) says the city “shall not require that those offstreet parking spaces be replaced”; LADBS puts it plainly: “If you remove covered parking to build an ADU, you don’t need to replace it.” For an ADU within existing space, section 66324 bars the city or the utility from requiring a new or separate utility connection unless the unit is built with a new house. Sprinklers follow the main house on both routes.

Detached: 800 square feet guaranteed, four-foot setbacks, height, solar

For a new detached unit, section 66323(a)(2) requires ministerial approval of one detached ADU of up to 800 square feet with four-foot side and rear setbacks, and section 66321 bars a city from applying any floor-area, lot-coverage or open-space standard that would prevent it. Height is at least 16 feet, or 18 feet within half a mile walking distance of a major transit stop, and under the City of Los Angeles ordinance a detached ADU can go to 1,200 square feet where the lot’s own standards allow; our Los Angeles ADU rules page and ADU rules calculator show what applies to your address. LADBS states that “detached ADUs built from scratch must have solar panels,” a state energy-code requirement a conversion does not carry. An ADU of 750 square feet or less is exempt from local impact fees on either route.

Standard plans and the 60-day clock

The LADBS ADU Standard Plan Program pre-approves complete designs for detached units, roughly 60 plans from 200 to 1,200 square feet including the city-owned YOU-ADU plan that owners may use free of charge, and plan check is then limited to site-specific items such as zoning and the foundation. A conversion starts from the garage you already have, so it goes through regular plan check with its own drawings; our guide to ADU standard plans in Los Angeles explains when the catalogue helps. Both routes get the same deadline under section 66317: the city must confirm within 15 business days that an application is complete and approve or deny it within 60 days, or it is deemed approved, with no hearing or neighbour notice.

What a garage conversion cannot fix

This is what decides most projects, and it is why the site walk comes before the price. Los Angeles County Building and Safety publishes standard notes for converting an existing single-story garage, and the same state building code applies inside the City of Los Angeles and in every other city we work in. Some of what those notes require can be fixed with money; some cannot be fixed at all.

• Ceiling height. Habitable rooms need a ceiling of at least 7 feet (California Residential Code R305.1). Most garages clear it at the plate but not always once a finished ceiling, insulation and a level floor go in. Raising the roof is possible, as on the 2025 project above, but at that point you are paying for framing and a roof anyway.
• Slab elevation and condition. The garage slab was poured to hold a car: it slopes toward the door, often sits below the house’s finished floor, and on older garages has no vapor barrier. The County notes allow a sound 3-inch slab as is and a sound 2-inch slab only with a 2-inch concrete topping, with an approved moisture barrier over it; a cracked, heaved or thin slab gets replaced. What cannot change is where the slab sits relative to the yard and the house, which fixes the floor level, the drainage and the step at the door.
• Footings. A garage’s continuous footing was sized for a garage. The County requires the pre-construction meeting to include “exposing a section of the foundation to verify existing footing depth” for the added anchoring and bracing, and the garage-door opening “shall be converted to a permanent wall and a new foundation at this location shall be installed and anchored to the existing continuous footing.” If the footing turns out to be shallow or broken, the conversion becomes a partial rebuild.
• Footprint and position. The unit sits where the garage sits, at the garage’s size plus 150 square feet. If the garage is 300 square feet or backs onto the neighbour’s bedroom, no design fixes that.
• Envelope and openings. Walls, roof and floor have to reach the residential energy standard (R-21 in 2×6 or R-15 in 2×4 walls in the County notes), a bedroom needs an egress window of 5.7 square feet net clear opening, and the unit needs light and ventilation openings a garage never had. On an attached garage the wall to the house becomes a one-hour fire-rated assembly from slab to roof sheathing.
• Sewer. The drain has to reach the lateral with fall; the County notes call for the connection at least 24 inches outside the existing foundation at a 2 percent slope. A garage downhill from the sewer, or far from it, means a pump or a long trench.
• Junior ADU (JADU) rules and cost in Los Angeles

None of this means conversions are a bad idea. It means the garage has to be looked at before it is priced, and the honest outcome of a site walk is sometimes “demolish and build new on the same footprint,” which keeps the no-setback benefit while solving the height, slab and footing problems at once.

Rent and value: what each one is worth

Tenants pay for a kitchen, a bathroom, light and privacy, not for how the building started, so a properly done conversion tends to rent like a detached unit of the same size, and a compromised one (low ceiling, small windows, a step down at the door) tends to rent for less. A larger detached unit with a second bedroom rents for more than any two-car garage can, and it can be placed for privacy from the main house in a way a garage on the driveway cannot. We do not publish rent figures because they vary by neighbourhood; HUD’s Fair Market Rents for Los Angeles County are a conservative benchmark, and our ADU financing guide shows how to compare net rent with the loan payment. On property tax, both routes are treated the same way: the county assessor values the new construction as of completion and adds only that amount, and the existing house is not reassessed. At resale, either unit sells with the house as a property with an income unit; a conversion also removes covered parking, which some buyers care about more than others.

When each one wins

Convert the garage when it is structurally sound, with a good slab, adequate ceiling height and a roof worth keeping; its size and position already suit a studio or one-bedroom of about 400 square feet; the lot has no room for a new building four feet off the lines, or the yard matters more to you than the garage; budget is the constraint and $100,000 to $200,000 is the number you can finance; or you want the shorter schedule.

Build a detached ADU when you want two bedrooms, higher ceilings or a unit over 550 square feet; the garage is too low, too small, badly placed or in poor condition, so a conversion would need a new roof, slab and footings anyway; you want to keep the garage for parking and storage; the lot is deep enough for a private unit away from the house; or rental value is the goal and a larger unit will carry the higher cost.

Demolish and rebuild on the garage footprint when the garage is in the right place but the wrong condition; a structure “constructed in the same location and to the same dimensions” keeps the no-setback benefit.

Run your address through the ADU rules calculator before you decide, and expect the site walk to check the slab, the ceiling, the footings, the panel and the sewer before any number is written.

Where we do this work

The choice between converting and building new shifts with the housing stock. Across the San Fernando Valley and the City of Los Angeles, 1950s to 1970s ranch houses come with detached two-car garages at the back of the lot that convert well when the slab and roof are sound, LADBS reviews both routes, and the standard plan catalogue is available for detached units. In Orange County, attached garages on 1970s to 1990s tract houses are common, HOA review applies to either project, and keeping covered parking often tips the decision toward a detached unit. Ventura County cities such as Thousand Oaks and Simi Valley run their own building divisions, and hillside lots often need a soils report for a new foundation. In western Riverside County and western San Bernardino County, the larger lots of Corona, Ontario and Rancho Cucamonga make both routes feasible, and expansive soils can call for a geotechnical report on a detached unit. See all of our service areas.

Detached ADU vs. garage conversion FAQs

Is it cheaper to convert a garage or build a detached ADU?

Converting a garage is usually cheaper: a garage conversion ADU in Los Angeles typically runs $100,000 to $200,000, while a detached ADU runs $180,000 to $260,000 for about 500 square feet and $300,000 to $450,000 or more for about 1,000 square feet. The gap narrows when the garage needs a new slab, footings or roof. These are typical Los Angeles budgeting estimates, not a price list or a quote; a real project can come in lower or higher.

Do I have to replace the parking if I convert my garage into an ADU?

No. Under California Government Code section 66314(d)(11), when a garage, carport or covered parking structure is converted to an ADU or demolished to build one, the city cannot require the lost off-street parking spaces to be replaced, and LADBS states the same rule for the City of Los Angeles. A detached ADU that leaves the garage standing keeps your covered parking.

Does a garage conversion ADU need setbacks?

No. A garage converted to an ADU within its existing footprint, or rebuilt to the same dimensions in the same location, needs no setback under Government Code section 66314(d)(7), and it may add up to 150 square feet for entry and exit under section 66323. A new detached ADU must sit at least four feet from the side and rear property lines. This is why a garage on the property line can become an ADU where a new building could not.

What can’t a garage conversion fix?

A garage conversion cannot change the slab’s elevation, the footprint’s size beyond 150 square feet of expansion, or its position on the lot, and it inherits the original footings and ceiling height. Habitable rooms need a ceiling of at least 7 feet, the garage-door opening must get a new foundation tied to the existing footing, and a thin or cracked slab needs topping or replacement. When those add up, demolishing and rebuilding on the same footprint keeps the no-setback benefit and solves all of them.

Does a detached ADU need solar panels?

Yes. LADBS states that detached ADUs built from scratch must have solar panels under the California energy code, while a garage conversion ADU does not carry that requirement because it is a conversion of an existing structure. The solar system is one of the items that makes a detached unit cost more than a conversion, alongside the new foundation, framing and roof.

Can I use an LADBS standard plan for a garage conversion?

No. The LADBS ADU Standard Plan Program pre-approves complete designs for new detached ADUs, so plan check is limited to site-specific review of zoning and foundation; a garage conversion starts from the garage you already have and goes through regular plan check with its own drawings. Both routes are covered by the state’s 60-day approval deadline for a complete application.

Convert it, rebuild it, or build new? Let us look at the garage first.

We will measure the ceiling, check the slab and expose the footing if needed, camera the sewer, check the panel and the setbacks, and tell you in writing whether your garage is worth converting, with a budgeting range for each route. The site visit and the estimate are free.

A room addition makes the house you live in bigger; an accessory dwelling unit (ADU) is a separate, self-contained home with its own kitchen, bathroom and entrance that can be rented, house a relative, or sit empty until you need it. In Los Angeles the two cost about the same per square foot, but they are governed by different rules, take different amounts of time, and answer different questions: an addition is the right choice when the new space must connect to your existing rooms, and an ADU is the right choice when you want income, independence for the occupant, or square footage your lot’s zoning would not otherwise allow. Green Design and Build is a licensed general contractor (CSLB #1110975) based in Van Nuys that designs and builds both, for homeowners across Los Angeles County, Orange County, Ventura County, western Riverside County and western San Bernardino County (Ontario, Rancho Cucamonga and neighbouring cities).

We are led by Dekel Sofer. We hold a 4.7-star rating across 146 Yelp reviews and have completed hundreds of projects across all five counties. Because we build room additions and ADUs with the same team, we have no reason to steer you toward one; the first job on a site walk is telling you which one your lot and your goal actually call for.

ADU vs. room addition at a glance

	Room addition	ADU
What it is	New square footage attached to and opening into the existing house	A separate dwelling with its own kitchen, bath and entrance: detached, attached, garage conversion or junior ADU inside the house
Best use	Primary suite, family room, kitchen expansion, second story; space you use every day	Rental income, a parent or adult child, a guest suite, a home office with privacy, future flexibility
Typical Los Angeles budgeting estimate	Ground floor $300–$500 per sq ft; second story $400–$650 per sq ft; $75,000 for a small bedroom to $650,000+ for a full second story	Garage conversion $100,000–$200,000; detached about 500 sq ft $180,000–$260,000; 700–800 sq ft $225,000–$350,000; about 1,000 sq ft $300,000–$450,000+; new construction $300–$450 per sq ft all-in
Zoning in the City of Los Angeles (R1)	Must fit the lot’s setbacks (typically 20 ft or prevailing front, 5 ft sides, 15 ft rear) and the 45 percent floor-area cap of the Baseline Mansionization Ordinance	State law requires approval of a detached ADU of up to 800 sq ft with 4 ft side and rear setbacks and 16 ft height (18 ft near major transit) regardless of the lot’s floor-area cap; the city allows up to 1,200 sq ft detached
Permit path	Building permit with full plan check, plus plumbing, electrical and mechanical permits; discretionary review in an HPOZ or hillside area	Ministerial approval: the city must approve or deny a complete application within 60 days; no hearing or neighbour notice
Timeline, start to finish	9–14 months	6–12 months
Can it be rented separately?	No; it is part of the house	Yes, on leases longer than 30 days; owner occupancy is not required for a standard ADU
Property tax	New construction is assessed and added; the existing house is not reassessed	Same rule: the ADU is assessed as new construction and added; the existing house keeps its base
Utilities	Extends the house’s systems; may need a panel upgrade	Usually shares the house’s water, sewer and panel; a 200-amp upgrade is common; separate electric meter optional
Resale	Sells as a larger house; value follows comparable larger homes on the street	Sells with the house as a property with an income unit; cannot be sold separately unless your city adopts a condominium ordinance under state law

These are typical Los Angeles budgeting estimates, not a price list or a quote. Your project can come in lower or higher depending on the house, the scope and the finishes; the only real number is a written proposal after a site visit. The addition figures are from our room addition cost guide and the ADU figures from our ADU cost guide.

Cost: close per square foot, different in total

Per square foot the two are close: $300 to $500 all-in for a ground-floor addition, $300 to $450 for a detached ADU, and past $500 for either on a difficult lot. The total is where they separate, because they are rarely the same size.

Project	Typical size	Typical Los Angeles budgeting estimate
Bedroom or home office addition, ground floor	200–350 sq ft	$75,000–$150,000
Primary suite with bathroom, ground floor	350–500 sq ft	$130,000–$250,000
Family room or kitchen expansion	300–500 sq ft	$110,000–$230,000
Partial second story	400–600 sq ft	$200,000–$350,000
Full second story	800–1,200 sq ft	$350,000–$650,000+
Garage conversion ADU	About 400 sq ft (two-car garage)	$100,000–$200,000
Detached ADU	About 500 sq ft	$180,000–$260,000
Detached ADU	700–800 sq ft	$225,000–$350,000
Detached ADU	About 1,000 sq ft	$300,000–$450,000+

These are typical Los Angeles budgeting estimates, not a price list or a quote. Your project can come in lower or higher depending on the house, the scope and the finishes; the only real number is a written proposal after a site visit.

An ADU always contains the two most expensive rooms in any house, a kitchen and a full bathroom, so a 400-square-foot ADU carries more plumbing, electrical and cabinetry than a 400-square-foot family room. On the other hand, a garage conversion starts with a slab, walls and a roof, which is why it sits at the bottom of every ADU range, and a detached unit does not disturb the house you live in, so there is no cost for tying a new roof into an old one or opening a bearing wall. A second-story addition is the most expensive space per square foot because the roof comes off and the framing below often has to be strengthened to carry it.

On either project, hold a contingency of 15 to 20 percent above the accepted bid, especially on a pre-1980 house. The 600-square-foot detached ADU retold in our ADU cost guide went from a $180,000 budget to about $265,000 after a clay sewer line under the new foundation had to be rerouted (about $14,000), the 100-amp panel became 200 amps ($6,000 to $8,000 and about three weeks waiting on the utility), and the owners added roughly $30,000 of finish upgrades. Every one of those can happen on an addition.

Rules: the ADU can go where the addition cannot

This is the difference that decides more projects than cost does.

The addition has to fit the zoning

In the City of Los Angeles, which includes most of the San Fernando Valley, a room addition on a typical R1 lot has to sit inside the lot’s setbacks, usually 20 feet or the prevailing setback at the front, 5 feet from each side property line and 15 feet from the rear, and under the Baseline Mansionization Ordinance’s cap on total floor area, 45 percent of the lot area on most R1 lots. A 1,500-square-foot house on a 6,000-square-foot lot is at 25 percent and has room; a 2,700-square-foot house on the same lot is at the limit and cannot add a room, regardless of what the yard looks like. Every addition goes through full plan check with plumbing, electrical and mechanical permits; an addition in a Historic Preservation Overlay Zone goes through the Office of Historic Resources, and hillside lots add grading review and usually a geotechnical report. Our room additions page walks through these rules.

The ADU is protected by state law

California Government Code section 66323 requires the city to approve, ministerially, one detached new-construction ADU of up to 800 square feet with four-foot side and rear setbacks on a lot with a single-family home, and section 66321 bars a city from applying any development standard, including floor-area ratio and lot coverage, that would prevent it. Height is at least 16 feet for a detached unit, 18 feet within half a mile walking distance of a major transit stop, and up to 25 feet or the zone’s limit for an attached unit; under the City of Los Angeles ordinance a detached ADU can go to 1,200 square feet where the lot’s own standards allow. A garage converted to an ADU needs no setback at all, and the city cannot require replacement parking. On a lot at its 45 percent limit, the ADU is the only new square footage available. Run your address through our ADU rules calculator or read the Los Angeles ADU rules page.

The permit clock

Section 66317 requires the city to tell you within 15 business days whether an ADU application is complete and to approve or deny a complete application within 60 days; if it does neither, “the application shall be deemed approved.” There is no equivalent deadline for a room addition, which is why plan check for an addition runs two to four months in our published timeline and a complete ADU submittal is usually through faster. Both wait on the same utility clearances.

Attached ADU versus addition: the grey area

An attached ADU is physically an addition with its own entrance, kitchen and bath, and a wall between it and the house. State law caps it at 50 percent of the existing house’s floor area, with an 800-square-foot floor the city must allow, and lets it rise to 25 feet or the zone height limit, whichever is lower. Homeowners who want a suite for a parent today and a rental in ten years often build an attached ADU rather than a primary-suite addition; the kitchen and the separate entrance are what make the space rentable later, and the cost of the kitchen is the price of that option.

Timeline: 9–14 months versus 6–12 months

Our published schedule for a room addition is 9 to 14 months from first meeting to final inspection: 6 to 10 weeks of design, engineering and Title 24 for a ground-floor addition (8 to 12 for a second story), 2 to 4 months of plan check, and 4 to 7 months of construction (5 to 7 for a second story). An ADU runs 6 months to a year, garage conversions at the short end and large detached units at the long end; our guide to how long an ADU takes breaks it down phase by phase.

The gap comes from two places. Plan check is shorter for an ADU because of the 60-day rule, and in the City of Los Angeles a detached unit can use one of the LADBS pre-approved standard plans, which limits plan check to site-specific items. Construction is also usually shorter for a detached ADU than for an addition of the same size because the crew is not working inside an occupied house: no protecting the existing rooms, no tying into a kitchen in use, no roof open over the family. A second-story addition is the extreme case, where the house is often unlivable for part of the build.

Rent, family and resale: what each one is for

An addition is used by the people who own the house, and its value at resale is the value of a larger house on that street; a primary suite or family room in a 1,200-square-foot Valley ranch house tends to bring it in line with the larger homes nearby, but it produces no income. An ADU is a separate dwelling: it can be rented long term (state law bars a city from requiring owner occupancy for a standard ADU, and rentals of state-exemption ADUs and junior ADUs must be longer than 30 days), it can house a parent with a real front door between the generations, and it can revert to family use later. At resale it is marketed as a property with an income unit, but it stays part of the same parcel; state law only lets an ADU be sold separately as a condominium where the city has adopted an ordinance under Government Code section 66342.

The property-tax treatment is the same for both: new construction is assessed at market value when completed and added as a supplemental assessment, and the existing house and land are not reassessed, so your Proposition 13 base stays where it is. Rent is the factor we will not put a number on; HUD’s Fair Market Rents for Los Angeles County and a local property manager are the right sources, and our ADU financing guide shows how to compare net rent against the loan payment.

How to decide

Work through these in order; most homeowners have an answer by the third question.

1. Does the new space have to open into the rooms you already have? A bigger kitchen, a family room off the living room, a second bathroom for the kids’ bedrooms: addition. Space used by someone else, or by you with a door between it and the house: ADU.
2. Do you want income, now or later? If yes, ADU; an addition never pays rent. If the answer is “maybe in ten years,” an attached ADU or a detached unit with a real kitchen keeps the option.
3. Is the lot at its floor-area limit or short on setbacks? If an addition does not fit under the 45 percent cap and the setbacks, the 800-square-foot ADU exemption is the square footage the state guarantees you.
4. Is there a garage you do not need for cars? A two-car garage of about 400 square feet is the lowest-cost route to an ADU, and the city cannot make you replace the parking. If you want the garage as part of the house instead, that is an addition and follows the addition rules.
5. Who is going to live in it? A parent who needs a bedroom near the family: addition or junior ADU inside the house. A parent who wants independence, an adult child, or a tenant: separate unit.
6. Can you live in the house during construction? An ADU does not disturb the house; a second-story addition is the slowest and most disruptive option and often means moving out for part of the build.
7. What will the neighbourhood pay for? On a street of 2,500-square-foot houses, taking a 1,300-square-foot house to 2,000 is value the market recognizes. On a street of small houses on large lots near transit, an income unit is what buyers pay for.

Can you do both?

Yes, and on many lots it is the right answer. State law allows a detached ADU of up to 800 square feet regardless of the lot’s floor-area cap, and a junior ADU of up to 500 square feet inside the house alongside it, so a homeowner can add a primary suite under the zoning rules and still build a detached unit in the yard under the ADU rules. One design and engineering package that covers both saves a second round of plan check, and the 200-amp panel and any sewer repair get sized once for the whole property. A common Valley plan is a garage conversion ADU now and a second-story addition later, once the rent is coming in; another is an attached ADU built as the parents’ suite with a detached rental behind it.

Where we do this work

The rules that decide between an ADU and an addition change with the address. Inside the City of Los Angeles and most of the San Fernando Valley, the 45 percent floor-area cap and the R1 setbacks apply to additions and LADBS reviews both projects, with the standard plan catalogue available for detached ADUs. In Orange County, each city sets its own floor-area and setback rules, and master-planned communities in Irvine and Anaheim Hills add HOA review, though state law voids covenants that prohibit or unreasonably restrict an ADU. Ventura County cities such as Thousand Oaks have their own building divisions and hillside lots that often need a soils report. In western Riverside County and western San Bernardino County, larger lots in Corona, Ontario and Rancho Cucamonga make a detached ADU and a ground-floor addition both feasible, and expansive soils can call for a geotechnical report. See all of our service areas.

ADU vs. room addition FAQs

Is an ADU cheaper than a room addition?

Per square foot they are close in Los Angeles: a ground-floor room addition typically runs $300 to $500 per square foot all-in and a detached ADU $300 to $450, while a second-story addition runs $400 to $650. In total an ADU often costs more than an addition of the same size because it always includes a kitchen and a full bathroom, and a garage conversion ADU at $100,000 to $200,000 is usually the lowest-cost route to a separate unit. These are typical Los Angeles budgeting estimates, not a price list or a quote; a real project can come in lower or higher.

Can I build an ADU if my lot is at its floor-area limit?

Yes. California Government Code sections 66321 and 66323 require a city to approve a detached ADU of up to 800 square feet with four-foot side and rear setbacks even where the lot’s floor-area ratio or lot coverage would block an addition of the same size. In the City of Los Angeles, a lot at the 45 percent Baseline Mansionization limit cannot add a room, but it can still build that ADU. Our ADU rules calculator shows what applies to your address.

Which adds more value, an ADU or an addition?

It depends on the street and the buyer. A room addition raises the value of the house toward the larger homes nearby; an ADU adds a separate dwelling that can produce rent and is marketed as a property with an income unit. Neither triggers a reassessment of your existing house; the county assessor adds only the value of the new construction. We do not publish value or rent figures because they vary by neighbourhood; an appraiser or agent who knows your street is the right source.

How long does an ADU take compared with a room addition?

An ADU in Los Angeles typically takes six months to a year from first meeting to move-in, and a room addition 9 to 14 months. The ADU is faster because state law requires the city to approve or deny a complete ADU application within 60 days and because construction does not disturb the occupied house, while plan check for an addition runs two to four months and a second-story addition can take five to seven months of construction alone.

Can I do a room addition and an ADU on the same lot?

Yes. The floor-area cap applies to the addition, and the state’s 800-square-foot ADU exemption applies to the ADU, so a homeowner can add a primary suite to the house and still build a detached unit in the yard, with a junior ADU of up to 500 square feet inside the house also allowed. Designing both on one set of drawings saves a second plan check and lets the panel upgrade and any sewer work be sized once for the whole property.

What is the difference between an attached ADU and a room addition?

An attached ADU is an addition with its own entrance, kitchen and bathroom, separated from the house by a wall, and it can be rented as a separate dwelling; a room addition opens into the existing house and is part of it. State law caps an attached ADU at 50 percent of the existing house’s floor area, with an 800-square-foot floor the city must allow, and lets it rise to 25 feet or the zone height limit. Homeowners who may want rental income later often choose the attached ADU and pay for the kitchen that makes it rentable.

Not sure whether your lot wants an ADU or an addition? Walk it with us.

We will check your setbacks and floor-area limit, camera the sewer, look at the panel and the garage, and tell you in writing which project fits your lot and your goal, with a budgeting range for each. The site visit and the estimate are free.

Most homeowners in Los Angeles finance an ADU with home equity: a home equity line of credit (HELOC), a home equity loan, or a cash-out refinance, and those who do not have the equity yet use a renovation loan or a construction loan that lends against the value of the property with the ADU finished. Green Design and Build is a licensed general contractor (CSLB #1110975) based in Van Nuys, not a lender; we build detached ADUs, garage conversions, attached ADUs and junior ADUs for homeowners across Los Angeles County, Orange County, Ventura County, western Riverside County and western San Bernardino County (Ontario, Rancho Cucamonga and neighbouring cities), and this guide explains the financing paths Los Angeles homeowners use so you know what to ask a lender for. Our published Los Angeles budgeting estimates run from $100,000 to $200,000 for a garage conversion ADU to $300,000 to $450,000 or more for a 1,000-square-foot detached unit; these are typical budgeting estimates, not a price list or a quote, and your project can come in lower or higher.

We are led by Dekel Sofer. We hold a 4.7-star rating across 146 Yelp reviews and have completed hundreds of projects across all five counties. Green Design and Build offers financing programs through Synchrony, Service Finance and Home Run Financing; terms depend on the lender and credit approval, and the details are on our financing page.

How much are you financing?

The loan has to fit the project, so start with the number. The ranges below are the ones published on our homepage and on our ADU cost guide.

ADU type and size	Typical Los Angeles budgeting estimate
Garage conversion ADU	$100,000–$200,000
Detached ADU, about 500 sq ft	$180,000–$260,000
Detached ADU, 700–800 sq ft	$225,000–$350,000
Detached ADU, about 1,000 sq ft	$300,000–$450,000+
Rule of thumb, new construction	$300–$450 per sq ft all-in
Difficult lots (hillside, poor access, long utility runs)	$500+ per sq ft

These are typical Los Angeles budgeting estimates, not a price list or a quote. Your project can come in lower or higher depending on the house, the scope and the finishes; the only real number is a written proposal after a site visit.

Two adjustments matter for the loan amount. First, our ADU cost guide recommends a contingency of 15 to 20 percent above the accepted bid; on the 600-square-foot detached ADU retold there, a $180,000 budget finished near $265,000 after a $14,000 sewer reroute, a $6,000 to $8,000 panel upgrade and about $30,000 of finish upgrades the owners chose after framing. Borrow the contingency up front; a HELOC you do not draw costs little, and a second loan mid-project costs time. Second, include the soft costs that come before construction: design, engineering, Title 24, plan check and permit fees, and any soils report. Our post on why ADU quotes vary so much between contractors explains what a complete quote includes, and our pricing page collects every range we publish.

ADU financing options compared

Option	What it is	Best for	Watch for
HELOC	A revolving line secured by your home’s equity; draw what you need, when you need it, usually at a variable rate	Owners with substantial equity who want to pay the contractor as milestones complete	Variable rate; draw period followed by a repayment period; the lender caps the line at a percentage of your current value
Home equity loan	A fixed-sum second mortgage at a fixed rate, funded in one lump sum	Owners who want a predictable payment and know the full budget	You pay interest on the whole amount from day one, even before construction starts
Cash-out refinance	A new first mortgage larger than your current one; you take the difference in cash	Owners whose existing rate is close to today’s rates, or who want one payment	Replaces your existing mortgage rate; closing costs on the full loan, not just the cash out
Renovation loan (FHA 203(k), Fannie Mae HomeStyle Renovation)	A purchase or refinance mortgage that includes the construction cost, underwritten on the as-completed value	Owners with limited current equity, buyers planning an ADU at purchase	Lender-managed draws, inspections and paperwork; contractor and plans must be approved before closing
Construction loan	A short-term loan funded in draws as work is completed, often converted to a permanent mortgage at the end	Larger detached units where current equity will not cover the budget	Interest-only during construction; draw inspections; typically higher rates and fees than equity products
Personal loan or contractor financing	Unsecured loan, or a program offered through lenders the contractor works with	Smaller scopes, bridging a gap, or owners who do not want a lien on the house	Shorter terms and higher rates than secured loans; amounts are usually smaller than an ADU budget
Cash and savings	No loan	Owners who have it, or a phased scope	Keep the contingency in reserve; do not fund the last 20 percent from money you have not got

Which one is right depends on your equity, your existing mortgage rate, your income and how fast you need the funds. We describe how each works below without rates, because rates change and lenders differ.

HELOC

A HELOC is the financing path homeowners use most often for an ADU because it matches how a construction contract is paid: in stages. You draw against the line as each progress payment comes due and pay interest only on what you have drawn. The lender sets the line as a percentage of your home’s appraised value minus your first mortgage, so an owner of a 1960s Valley house bought a decade ago usually has room; an owner who bought in the last two years may not. Most HELOCs carry a variable rate and a draw period followed by a repayment period, so ask what the payment looks like once the draw period ends.

Home equity loan

A home equity loan is a second mortgage for a fixed amount at a fixed rate, funded in a lump sum. It suits an owner who wants a payment that does not move and a budget already settled by a site walk and a written proposal. The trade-off is interest on the full amount from closing, including money that sits in the bank for months waiting for plan check.

Cash-out refinance

A cash-out refinance replaces your existing mortgage with a larger one and hands you the difference. It only makes sense when the new rate is close to the one you have; an owner with a low-rate mortgage from a few years ago usually keeps it and adds a second lien instead. It does give you one payment and a fixed rate on the whole balance.

Renovation loans: FHA 203(k) and Fannie Mae HomeStyle Renovation

Renovation loans are the route for homeowners who do not have the equity today but will once the ADU exists, because the lender underwrites against the as-completed appraised value. The FHA 203(k) program lets homebuyers and homeowners finance repairs and improvements into the mortgage; the Limited 203(k) is capped at $75,000 of improvement cost, so an ADU usually needs the Standard 203(k). Since October 2023, FHA has allowed lenders, for some borrowers, to count 50 percent of the estimated rental income from a new ADU the borrower plans to add under a Standard 203(k) toward qualifying, and 75 percent of the estimated rent from an existing ADU. Fannie Mae’s HomeStyle Renovation mortgage lets a borrower “purchase a property or refinance an existing loan and include funds in the loan amount to cover the costs of repairs, remodeling, renovations, or energy improvements,” and Fannie Mae’s guide states it may be used to construct accessory units where local zoning allows. Both programs require plans, a contractor the lender accepts and a cost breakdown before closing, and both pay the contractor through lender-controlled draws with inspections. Ask the lender specifically whether the loan can be used for a detached ADU on your lot and how ADU rental income is treated in qualifying; the rules differ by program and lender.

Construction loans

A construction loan funds the build in draws tied to completed work, with interest-only payments during construction, and usually converts to a permanent mortgage when the ADU is finished. It is the tool for a larger detached unit when equity will not cover the budget and a renovation loan does not fit. Expect the lender to require the full plan set, the building permit, our written proposal and schedule, and an inspection before each draw, so design and permitting should be well along before you apply; our guide to how long an ADU takes shows where in the calendar that is.

Personal loans and contractor financing

Unsecured personal loans close fast and put no lien on the house, but the amounts and terms rarely fit a full ADU budget; they are more often used for a contingency or the last stretch of a phased project. Green Design and Build offers financing programs through Synchrony, Service Finance and Home Run Financing; terms depend on the lender and credit approval. We do not set the rates and we cannot promise approval.

Cash

Paying cash avoids interest and closing costs, but it removes the discipline a lender’s draw schedule imposes. Keep the 15 to 20 percent contingency in a separate account and pay on the same milestone schedule you would with a lender.

How the contract and the draw schedule shape your payments

Whatever loan you use, California law fixes the shape of the payments. Under Business and Professions Code section 7159, a home improvement contract must state that “the downpayment may not exceed $1,000 or 10 percent of the contract price, whichever is less,” and that “it is against the law for a contractor to collect payment for work not yet completed, or for materials not yet delivered.” Change orders become part of the contract only when written and signed by both parties before the work starts. So a legitimate ADU contract in Los Angeles has a small deposit, progress payments tied to milestones such as foundation, framing, rough inspections, drywall and final, and written change orders for anything discovered along the way.

For financing, three things follow:

1. Your loan has to fund in stages. A HELOC or a construction loan does that natively. A home equity loan or cash-out refinance funds once, so the money sits until each milestone; a renovation loan funds through the lender’s own draw process, which you and we both follow.
2. Milestones drive interest. On a HELOC, a project that finishes in seven months costs less interest than the same project at twelve; on a lump-sum loan the interest clock runs regardless. Read the schedule in our ADU timeline guide with the loan in hand.
3. Change orders need funded money behind them. On the $180,000 project that finished at $265,000, every increase was a written change order for a real condition or a real upgrade. An owner with the contingency in the HELOC approves a change order in a day; an owner who has to go back to the lender waits, and the crew waits with them.

Does the rent pay for the loan?

For a rental ADU the question is whether the rent covers the payment. The honest way to answer it is arithmetic with your own lender’s payment figure, not a number from a contractor’s brochure. Our ADU rental income guide puts HUD’s FY 2026 Fair Market Rents for each county against typical build costs.

• Start with realistic rent. The U.S. Department of Housing and Urban Development publishes Fair Market Rents for Los Angeles County by bedroom count each year at https://www.huduser.gov/portal/datasets/fmr.html; those figures are a conservative floor for a new studio or one-bedroom, and a local property manager will give you a market figure for your neighbourhood.
• Subtract what the tenant does not pay. Vacancy, the ADU’s share of property tax, insurance, maintenance and any utilities you keep in your name. Most ADUs share the house’s water, sewer and panel, so decide early whether you want a separate electric meter for the tenant.
• Compare net rent to the loan payment. If net monthly rent covers the payment on the loan you actually used, the unit carries itself; if not, the gap is the price of the space, the family use or the long-term value.
• Count the property-tax change correctly. Building an ADU in California does not trigger a reassessment of the existing house; the county assessor values the new construction as of completion and adds only that amount as a supplemental assessment, so your Proposition 13 base on the main house stays where it is.
• Ask about rental income in qualifying. Some FHA and conventional programs let a lender count a portion of projected or existing ADU rent toward your income; the percentages and conditions differ by program, so raise it in the first conversation.

State law bars a city from requiring owner occupancy for a standard ADU, and rentals of state-exemption ADUs and JADUs must be for terms longer than 30 days, so plan on a lease rather than a short-term rental.

What lenders will ask us for

Every lender that funds construction wants the same package, and we prepare it as part of the project: a written feasibility summary from the site walk with the budgeting range; the plan set, engineering and building permit; an itemized proposal with allowances, exclusions, the progress-payment schedule and the change-order procedure required by section 7159; our licence, bond and insurance details (verify CSLB #1110975 on the CSLB site); and a construction schedule with milestones the lender can tie draws to. Renovation and construction lenders may also require lien releases at each draw and an inspection before funds are released.

Choosing the right ADU financing

• Plenty of equity and a low existing mortgage rate: HELOC, or a home equity loan if you want a fixed payment.
• Existing rate close to today’s rates: compare a cash-out refinance against a HELOC on total cost, not just the rate.
• Thin equity but a property that will appraise well when finished: a renovation loan (Standard 203(k) or HomeStyle Renovation) or a construction loan; if you are buying the house now, a renovation loan at purchase covers both in one closing.
• Most of the money and a small gap: contractor financing or a personal loan for the gap.
• Unsure the unit pencils out: do the rent arithmetic above first, and consider a garage conversion at the bottom of the budget range before a detached unit at the top.

We are a builder, not a lender or a financial adviser, and the right loan depends on facts about your finances we do not see. Talk to at least two lenders, bring our feasibility summary, and ask each for the total cost of the loan over the life of the project, not the rate alone.

Where we do this work

Financing an ADU works the same across our service area; the budget it has to cover does not. Inside the City of Los Angeles and the San Fernando Valley, a detached unit can use an LADBS pre-approved standard plan and older Valley houses usually need the 200-amp panel upgrade in the budget. In Orange County and Ventura County, each city runs its own building division and HOA review in master-planned communities adds time, so a HELOC in place before design starts avoids paying interest on idle money. In western Riverside County and western San Bernardino County, newer houses in Corona, Ontario and Rancho Cucamonga tend to have larger lots and 200-amp service already, which keeps a detached unit nearer the bottom of its range. See all of our service areas.

ADU financing FAQs

How much does it cost to build an ADU in Los Angeles?

A garage conversion ADU in Los Angeles typically runs $100,000 to $200,000, a detached ADU of about 500 square feet $180,000 to $260,000, and a detached unit of about 1,000 square feet $300,000 to $450,000 or more, with new construction at roughly $300 to $450 per square foot all-in. These are typical Los Angeles budgeting estimates, not a price list or a quote; a real project can come in lower or higher, and the only real number is a written proposal after a site visit.

What is the best way to finance an ADU?

For most Los Angeles homeowners with equity, a HELOC is the best fit for financing an ADU because you draw funds as each progress payment comes due and pay interest only on what you have used. A home equity loan or cash-out refinance suits owners who want a fixed payment, and a renovation or construction loan suits owners whose equity will not cover the budget until the ADU is finished. The right choice depends on your equity, your existing mortgage rate and your income, so compare at least two lenders.

Can I use an FHA 203(k) loan to build an ADU?

Yes, an FHA Standard 203(k) loan can finance an ADU as part of a purchase or refinance, with the improvement cost included in the mortgage; the Limited 203(k) is capped at $75,000 of improvements, which is below most ADU budgets. Since October 2023, FHA has let lenders count, for some borrowers, 50 percent of the estimated rental income from a new ADU built under a Standard 203(k) toward qualifying. The lender approves the plans and the contractor before closing and pays for the work through inspected draws.

Does Green Design and Build offer financing for ADUs?

Green Design and Build offers financing programs through Synchrony, Service Finance and Home Run Financing; terms depend on the lender and your credit approval. We are a builder, not a lender, so we cannot promise approval or quote a rate. For a full ADU budget most homeowners use home equity, a renovation loan or a construction loan, and we provide the feasibility summary, plans, proposal and schedule those lenders require.

How much can I put down on an ADU contract in California?

Under California Business and Professions Code section 7159, the down payment on a home improvement contract may not exceed $1,000 or 10 percent of the contract price, whichever is less, and a contractor may not collect payment for work not yet completed or materials not yet delivered. The rest of an ADU contract is paid in progress payments tied to milestones, which is why a loan that funds in stages, such as a HELOC or construction loan, matches the contract well.

Will building an ADU raise my property taxes?

Building an ADU in California adds the assessed value of the new construction to your property tax bill but does not trigger a reassessment of your existing house and land, so your Proposition 13 base on the main home stays where it is. The county assessor values the ADU as of completion and bills the difference as a supplemental assessment. The Los Angeles County Assessor publishes ADU guidance and can estimate the effect for your project.

Get the numbers your lender will ask for

Before you apply for anything, we will walk your lot, camera the sewer, check the panel and give you a written feasibility summary with a budgeting range, a phase schedule and the itemized proposal that HELOC, renovation and construction lenders require. The site visit and the estimate are free.

An ADU in Los Angeles takes six months to a year from the first site walk to move-in: roughly one to two months of feasibility and design, one to three months of plan check and utility clearances, and three to eight months of construction depending on whether you are converting a garage or building a detached unit from the ground up. Green Design and Build is a licensed general contractor (CSLB #1110975) based in Van Nuys that designs, permits and builds detached ADUs, attached ADUs, garage conversions and junior ADUs for homeowners across Los Angeles County, Orange County, Ventura County, western Riverside County and western San Bernardino County (Ontario, Rancho Cucamonga and neighbouring cities). The phase durations on this page are typical Los Angeles planning ranges, not a promise; the two things that most often push a project past a year are utility work and what the site walk did not catch.

We are led by Dekel Sofer. We hold a 4.7-star rating across 146 Yelp reviews and have completed hundreds of projects, and we build across all five counties from our office at 16120 Sherman Way. Our ADU page covers the four unit types and what we check on a site walk; this guide is only about the calendar.

The short answer by ADU type

ADU type	Typical time from first meeting to move-in	Why
Garage conversion	Shorter end of six months to a year	No foundation, framing or roof phase; construction runs about three to five months
Junior ADU (inside the house, up to 500 sq ft)	Usually the shortest	Existing space, efficiency kitchen, often no new utility service
Attached ADU (addition with its own entrance)	Middle of the range	New foundation and framing, but shares walls, roof and utility runs with the house
Detached ADU (new backyard unit)	Longer end of six months to a year	Everything is new: foundation, framing, roof, solar, trenching for water, sewer and power

The six-months-to-a-year figure is the one published on our homepage and it holds up because the middle of the schedule, plan check, is governed by a state deadline that does not care what kind of unit you are building. The ends of the schedule are what change: a detached unit needs more design and engineering up front and more months of construction at the back. A conversion skips both. Our garage conversion cost guide shows the stage-by-stage schedule for a conversion, and our ADU cost guide covers the dollars.

ADU timeline phase by phase

The table is how a typical fully permitted ADU in our service area moves through the calendar. Some phases overlap: utility applications go in during plan check, and a panel upgrade can happen while drawings are still being corrected.

Phase	Typical duration	What happens
Feasibility and site walk	1–3 weeks	Zoning and lot check against state minimums, sewer camera, panel and service check, survey if lot lines are unclear, written feasibility summary and budgeting range
Design and engineering	4–8 weeks	Floor plans, elevations, site plan, selections; or choosing an LADBS pre-approved standard plan for a detached unit in the City of Los Angeles
Engineering and Title 24	Runs inside the design phase	Structural calculations, foundation design, energy compliance forms, soils report where the lot requires one
Plan check and permit	Up to 60 days from a complete application, plus corrections	City of Los Angeles through LADBS; other cities through their own building divisions. State law sets the deadline (below)
Utility clearances	Overlaps plan check; about 3 weeks for a panel upgrade on the project we describe below	LADWP inside the City of Los Angeles; Southern California Edison or the city utility elsewhere; sewer connection review; water service
Construction	3–5 months (garage conversion) or 5–8 months (detached)	Foundation, framing, utilities, inspections, insulation, drywall, finishes, final inspection
Final inspections and occupancy	1–2 weeks	Final building, electrical, plumbing and mechanical inspections; certificate of occupancy; address and meter set-up if applicable

The conversion figures in this table are the ones on our garage conversion cost guide. The feasibility and detached-design durations are our working planning ranges, and they are the part of the schedule you control: a homeowner who has chosen a floor plan, a finish level and a budget before design starts shortens design by weeks.

The 60-day rule, and why plan check still takes longer

California Government Code section 66317 requires the permitting agency to tell you in writing within 15 business days whether your ADU application is complete, and then to approve or deny a complete application within 60 days. If the agency does neither within 60 days, “the application shall be deemed approved.” A denial has to come back with a written list of what is deficient and how to fix it. Because the review is ministerial, there is no hearing, no neighbour notice and no discretionary design review for a unit that meets the state standards; our ADU rules pages and ADU rules calculator show what those standards are for your city.

That is the legal floor, and it is why an ADU is faster to permit than a room addition, where plan check runs two to four months. It is not the same as a permit in 60 days, for three reasons:

1. The clock starts at “complete.” A submittal missing the Title 24 forms, a site plan with dimensioned setbacks, or the structural calculations does not start the clock. The 15-business-day completeness check is where incomplete packages lose a month.
2. Corrections restart the conversation. Plan check comments come back, the drawings are revised and resubmitted, and each cycle takes time on both sides. A clean, complete first submittal is worth more than any expediter.
3. Clearances run alongside. Planning clearance, the fire department in a fire zone, hillside grading review, a Historic Preservation Overlay Zone review through the Office of Historic Resources, and the utility applications each have their own queue. The building permit is not issued until they are cleared, and none of them is bound by the 60-day rule.

In the City of Los Angeles, a detached unit built from one of the roughly 60 LADBS pre-approved standard plans skips the design review of the building itself; LADBS reviews only the site-specific items, which “reduces the time required for plan check resulting in faster permit issuance.” LADBS does not promise a number of weeks saved, and neither do we, but a standard plan removes the corrections cycles that come from a custom design.

What delays an ADU in Los Angeles

Every phase in the table can run long, but the same handful of items cause most of the overruns we see. They are all things we look for on the first site walk.

Electrical service and the panel

Many 1950s to 1970s houses in the San Fernando Valley and the older parts of Orange County run on a 100-amp panel that is already carrying the main house. An ADU with a kitchen and a heat pump usually means a 200-amp service upgrade, and that upgrade is scheduled around the utility, not around you. On the 600-square-foot detached ADU in our ADU cost guide, the panel upgrade cost $6,000 to $8,000 and added about three weeks of delay “while waiting on the utility company’s timeline.” Inside the City of Los Angeles the service change goes through LADWP; in Orange County, Ventura County, western Riverside County and western San Bernardino County it goes through Southern California Edison or the city’s own utility. The work is performed by licensed electricians and scheduled and supervised by us as your general contractor; our electrical page explains the panel work. Filing the utility application during plan check, not after the permit, is how we keep it off the critical path.

The sewer lateral

A detached ADU needs a drain line to the street or to the house lateral, and on the same project above the excavation for the new foundation uncovered an old clay sewer line with cracks and root intrusion. Rerouting it cost approximately $14,000 and added work nobody had scheduled. A camera inspection before design costs a fraction of that and turns a surprise into a line item. The plumbing is performed by licensed plumbers and scheduled and supervised by us; see our plumbing page.

Soils, slope and hillside review

A flat Valley lot with a two-car driveway needs no soils report. A hillside lot in Sherman Oaks, Encino or Studio City, a sloping lot in Glendale or Thousand Oaks, or a property with a retaining wall between the house and the ADU site usually needs a geotechnical report before the foundation can be engineered, and in the City of Los Angeles a hillside lot goes through additional grading and access review. That adds weeks at the front of the schedule and can add a month or more of foundation work at the back.

Fire hazard zones

Since CAL FIRE’s March 2025 maps, much of the hillside Valley, the Santa Monica Mountains and the Orange County canyons sit in a Very High Fire Hazard Severity Zone. An ADU there is built to Chapter 7A of the building code: ember-resistant vents, Class A roof assembly, tempered or multi-pane glazing, and protected eaves. None of that is slow to build, but the fire department review is a separate clearance, and the materials have longer lead times than standard products.

HOA and CC&R review

Civil Code section 4751 makes any covenant that “effectively prohibits or unreasonably restricts” an ADU on a single-family lot void and unenforceable, but it still allows reasonable restrictions, and it does not remove the architectural review step. In master-planned communities in Irvine, Anaheim Hills, Rancho Cucamonga and Corona, plan on a review cycle before you submit to the city, and get it started during design rather than after.

Selections and change orders

The single largest cost movement on the project above was not a hidden condition: the owners added roughly $30,000 of finish upgrades after framing. Changes after rough-in are also the most common self-inflicted delay, because tile, cabinets and fixtures ordered late arrive late. Choose finishes before drywall, and expect custom cabinetry to take about three weeks to manufacture.

A real detached ADU that went from $180,000 to $265,000

The project we keep referring to is retold in full in our ADU cost guide. The homeowners had already removed an old, deteriorated garage and planned a roughly 600-square-foot one-bedroom, one-bath detached ADU on a budget of approximately $180,000. Three things moved it to about $265,000: the clay sewer line found under the new foundation (about $14,000 to reroute), the 200-amp panel upgrade ($6,000 to $8,000 and around three weeks waiting on the utility), and approximately $30,000 in finish upgrades chosen after framing. Two of the three were schedule problems as much as budget problems, and both are now standard checks on our site walk. Those figures, like every cost range we publish, are typical Los Angeles budgeting estimates, not a price list or a quote; a project can come in lower or higher. For a garage conversion, the equivalent story is the two-car garage in why ADU quotes vary so much that went from an $85,000 to $95,000 estimate to about $130,000 after the slab, the panel and the sewer were opened up.

A finished example of the conversion route is our garage-to-ADU conversion in Los Angeles, completed in 2025: a plain stucco garage of about 500 square feet with one wide door opening became a self-contained rental with a rebuilt roof structure, new framing and sheathing, new windows and French doors, a full kitchen and a full bathroom.

How to keep an ADU on schedule

• Do the feasibility work first. Sewer camera, panel check, lot-line and setback check, fire-zone and hillside status. Every item found here is a change order avoided later.
• Decide what the unit is for before design. A rental studio, a parent’s suite and a home office want different floor plans, and changing your mind after engineering costs weeks.
• Submit a complete package. Title 24, structural calculations, dimensioned site plan, and the soils report if the lot needs one. The 60-day clock only starts on a complete application.
• File utility applications during plan check. Service upgrades are on the utility’s calendar; the earlier the application, the less it matters.
• Finalize selections before rough-in. Cabinets, tile, fixtures, windows and doors with long lead times should be ordered while framing is still going up.
• Use a standard plan in the City of Los Angeles if one fits. For a detached unit, the LADBS catalogue avoids the design corrections that slow custom plan check.
• Hold a contingency. Our ADU cost guide recommends 15 to 20 percent above the accepted bid; a contingency also buys schedule, because a funded change order is approved in a day and an unfunded one waits.

Financing has a calendar too. A HELOC or a construction loan with a draw schedule needs to be in place before the deposit, which under California law is capped at $1,000 or 10 percent of the contract price, whichever is less; our financing page explains the programs we offer.

Where we do this work

An ADU schedule depends on who reviews it. Inside the City of Los Angeles and most of the San Fernando Valley, plans go to LADBS, the utility is LADWP, and detached units can use the standard plan catalogue. In Orange County every city runs its own building division and master-planned communities add HOA review before submittal. Ventura County cities such as Thousand Oaks and Simi Valley review their own permits, with Ventura County Building and Safety covering unincorporated areas, and hillside lots there often need a soils report. In western Riverside County and western San Bernardino County, Corona, Riverside, Ontario and Rancho Cucamonga have their own departments, newer housing stock with 200-amp panels already in place, and expansive soils that can require a geotechnical report. See all of our service areas.

ADU timeline FAQs

How long does it take to build an ADU in Los Angeles?

A fully permitted ADU in Los Angeles typically takes six months to a year from the first site walk to move-in. Feasibility and design take one to three months, plan check and utility clearances one to three months, and construction three to five months for a garage conversion or five to eight months for a detached unit. Hillside, fire-zone and historic reviews, and utility service upgrades, are the usual reasons a project runs toward the long end.

How long does ADU plan check take in Los Angeles?

Under California Government Code section 66317, the city must tell you within 15 business days whether your ADU application is complete and then approve or deny a complete application within 60 days, or it is deemed approved. In practice plan check runs one to three months once corrections cycles and planning, fire and utility clearances are included. A complete first submittal is the single biggest factor in staying near 60 days.

Is a garage conversion faster than a detached ADU?

Yes. A garage conversion ADU in Los Angeles sits at the shorter end of the six-month to one-year range because there is no foundation, framing or roof phase, and construction typically takes three to five months. A detached ADU needs more design and engineering up front and more months of construction, so it sits at the longer end. Both go through the same 60-day plan check rule.

What is the biggest cause of ADU delays?

Utility work is the most common cause of ADU delays in Los Angeles. On a detached ADU project we have written about, a 100-amp to 200-amp panel upgrade added about three weeks waiting on the utility, and an old clay sewer line found under the new foundation added unplanned excavation. Filing the utility application during plan check and running a sewer camera before design are the two best ways to avoid both.

Does an LADBS standard plan make an ADU faster?

Using one of the LADBS pre-approved standard plans for a detached ADU in the City of Los Angeles lets plan check focus on site-specific items such as zoning and foundation, which LADBS says reduces plan check time and results in faster permit issuance. LADBS does not state a specific number of weeks saved. Standard plans apply to new detached units, not to garage conversions, which go through regular plan check with their own drawings.

How much time should I add for a hillside or fire-zone lot?

A hillside lot in Los Angeles usually needs a geotechnical report before the foundation can be engineered, which adds weeks at the front of an ADU schedule, and hillside grading review is a separate clearance from the building permit. A lot in a Very High Fire Hazard Severity Zone adds a fire department review and Chapter 7A materials with longer lead times. Neither changes the 60-day plan check rule, but both add clearances that run outside it.

Find out how long your ADU will take before you commit

Give us your address and what you want the unit to do, and we will walk the lot, camera the sewer, check the panel and the fire-zone and hillside status, and give you a written feasibility summary with a phase-by-phase schedule for your property. The site visit and the estimate are free.

A garage conversion ADU in Los Angeles typically costs $100,000 to $200,000, and most two-car conversions we price land between $98,000 and $150,000 once the kitchen, bathroom, insulation, electrical and plumbing are included. Green Design and Build is a licensed general contractor (CSLB #1110975) based in Van Nuys that designs, permits and builds garage conversion ADUs for homeowners across Los Angeles County, Orange County, Ventura County, western Riverside County and western San Bernardino County. Every figure on this page is either already published on our site or simple arithmetic from those figures; none of it is a quote for your garage.

Green Design and Build is led by Dekel Sofer. We hold a 4.7-star rating across 146 Yelp reviews and have completed hundreds of projects. A standard two-car garage in the San Fernando Valley is usually around 400 square feet, already has a slab, walls and a roof, and often sits on a lot where a new detached unit would not fit.

Garage conversion cost by scope

The table puts the figures we have already published side by side so you can see where a conversion sits against the other routes to a legal ADU. All are typical Los Angeles budgeting ranges, not a quote.

Scope	Typical Los Angeles range
Garage conversion ADU, most two-car garages (about 400 sq ft), kitchen, bathroom, builder-grade finishes	$98,000 to $150,000
Garage conversion ADU, full range including detached garages needing trenching, sewer work, a panel upgrade or upgraded finishes	$100,000 to $200,000
Same 400 sq ft garage at the all-in ADU rule of thumb of $300 to $450 per sq ft	$120,000 to $180,000
Attached ADU (new space added to the house)	$150,000 to $300,000
Detached new-construction ADU, 500 sq ft	$180,000 to $260,000
Detached new-construction ADU, any size	$180,000 to $550,000 depending on size

These are typical Los Angeles budgeting estimates, not a price list or a quote. Your project can come in lower or higher depending on the house, the scope and the finishes; the only real number is a written proposal after a site visit.

A $98,000 to $150,000 conversion of a 400 square foot garage works out to roughly $245 to $375 per square foot, below the $300 to $450 per square foot we quote for new construction, and that gap is the whole reason to convert rather than build. But the top of the conversion range overlaps the bottom of the detached range: a detached garage at the back of a deep Valley lot, with a cracked slab, a 100-amp panel and a clay sewer lateral, can cost as much as a small new unit. The garage is a head start, not a discount.

The savings are specific: no foundation, no framing, no roof, and none of the solar panels that LADBS notes are required on detached ADUs built from scratch. What you still pay for is everything that makes a garage a home, which our ADU cost guide lists plainly: insulation, electrical, plumbing, HVAC, a complete kitchen, a full bathroom, code-compliance upgrades, windows and finishes. A kitchen and a bathroom are the two most expensive rooms in any house, and a 400 square foot ADU has both.

What changes the price of a garage conversion

When two quotes for the same garage are far apart, one of them usually skipped or deferred one of the items below. These are what we look at on the first site walk.

The slab and the moisture barrier

A garage slab was poured to hold a car, not a bedroom. Many older Valley slabs have no vapor barrier beneath them, slope toward the door, or sit below the finished floor of the house. In the conversion we describe in why ADU quotes vary so much, the slab “did not have a proper moisture barrier below it,” and correcting that meant additional preparation, materials, labor and concrete work before any framing started.

Sewer and plumbing

A garage has no drain, and a kitchen and bathroom need one. On an attached garage the tie-in is short; on a detached garage it can mean trenching across the yard, which is why our ADU cost guide notes that detached conversions typically cost more than attached ones. The lateral itself is the bigger risk: in the quote-variation post a camera inspection found “root intrusion and bellying,” and a section of sewer had to be replaced before the ADU could connect; in our ADU cost guide a cracked clay sewer line cost approximately $14,000 to reroute. We camera the lateral before we price the plumbing, which is performed by licensed plumbers and scheduled and supervised by us as your general contractor; see our plumbing page.

The electrical panel

Most 1950s to 1970s Valley houses still run on a 100-amp panel that is already at capacity. Add an electric range, a heat pump and a subpanel for the ADU and the main service has to grow to 200 amps. In our ADU cost guide that upgrade ran $6,000 to $8,000 and added around three weeks of delay for permitting, inspections and utility coordination. It is performed by licensed electricians and scheduled and supervised by us; our electrical page covers the panel and circuit work.

Door opening, insulation, windows and fire separation

The garage door span has to be framed in as a real wall with a header, sheathing and stucco that matches the house. Walls, roof and often the floor need insulation to the residential Title 24 standard, a bedroom needs an emergency escape window, and the unit needs light and ventilation openings a garage does not have. On an attached garage, the wall and any ceiling shared with the house must meet the code’s separation requirements between dwelling units, usually a rated assembly and a self-closing door. A quote that says “insulate and drywall” with no line for these is not describing a legal ADU.

Kitchen, bathroom and finishes

This is where most of the money goes and where most of the movement happens after signing. In the $180,000 to $265,000 project in our ADU cost guide, the homeowner added approximately $30,000 in finish upgrades once framing was done: a better tile package, solid-surface counters instead of laminate, better cabinetry and upgraded HVAC. That is why we recommend a 15 to 20 percent contingency on top of any base bid, and why you should ask what allowance a quote carries for cabinets, tile, fixtures and appliances.

The ADU rules that shape a garage conversion budget

California’s ADU statute now lives in Government Code sections 66310 to 66342. We verified each rule below against the code and the state’s guidance; the sources are listed at the end.

You do not have to replace the parking

When a garage, carport or covered parking structure is converted to an ADU, the local agency “shall not require that those offstreet parking spaces be replaced” (Government Code 66314(d)(11)). LADBS puts it plainly: “If you remove covered parking to build an ADU, you don’t need to replace it.” That removes what used to be the biggest hidden cost of a conversion, a new carport or driveway pad.

Setbacks do not apply inside the existing footprint

No setback is required for an existing accessory structure converted to an ADU (Government Code 66314(d)(7)). Under the state-exemption category for conversions, the unit must be within the existing space of the structure with side and rear setbacks “sufficient for fire and safety,” and may add up to 150 square feet for ingress and egress (Government Code 66323(a)(1)). A garage a foot off the rear property line can become an ADU where a new building could not, as long as fire separation is handled in the wall assembly. The four-foot setback is for new detached units. Our ADU rules calculator walks through what applies to your lot.

Fire sprinklers follow the main house

ADUs “shall not be required to provide fire sprinklers if they are not required for the primary residence” (Government Code 66314(d)(12); the same language appears in section 66323). Most existing single-family homes in Los Angeles have no sprinklers, so most garage conversions do not need them. If the main house is sprinklered, the ADU will be too.

The City’s standard plans are for new detached units

The LADBS ADU Standard Plan Program pre-approves complete designs, from studios of about 200 square feet to three-bedroom units of 1,200 square feet, in one- and two-story detached configurations. A conversion starts from the garage you already have, so it does not use a standard plan and goes through regular plan check with its own drawings. Our guide to ADU standard plans in Los Angeles explains when the catalogue helps and when a custom design is faster.

Impact fees, utility connections and the 60-day clock

An ADU of 750 square feet or less is exempt from local impact fees. For an ADU converted from existing space, the city and the utility cannot require a new or separate utility connection, or a connection fee or capacity charge, unless the ADU is built with a new single-family home (Government Code 66324); a separate electric meter for a rental is your choice, not a requirement. Once a complete application is filed, the agency must approve or deny it within 60 days or it “shall be deemed approved,” and a denial must list what is deficient (Government Code 66317). The word that matters is complete: a submittal missing Title 24 forms or a site plan does not start the clock.

How long does a garage conversion take?

Our published guidance for ADUs is six months to a year, and our garage conversion service page says most projects run several months from planning through completion. A conversion sits at the shorter end because there is no foundation or framing phase. The stage durations below are our working estimates, not published figures.

Stage	Typical time
Site walk, sewer camera, panel check, design and written proposal	Four to eight weeks
Plan check (City of Los Angeles through LADBS, or the local building division)	Up to 60 days from a complete application under state law
Electrical service upgrade, if needed	About three weeks, often overlapping plan check
Construction: demolition, slab work, framing, rough trades, inspections, insulation, drywall, kitchen and bath, finishes	Three to five months
Final inspections and certificate of occupancy	One to two weeks

The biggest schedule risks are what the camera finds in the sewer and what the utility says about the panel. Both are cheaper to learn before the contract than after demolition.

A real garage conversion that rose 40 percent

In why ADU quotes vary so much between contractors, we describe a homeowner converting a detached two-car garage, roughly 400 square feet, into a one-bedroom ADU with a kitchen, bathroom, bedroom and laundry area. The original estimate was $85,000 to $95,000. Three discoveries moved it to about $130,000, an increase of roughly 40 percent: the slab had no proper moisture barrier and needed preparation and concrete work; the home’s 100-amp panel was already insufficient and had to be upgraded to 200 amps; and a camera inspection found root intrusion and bellying in the sewer, so a section had to be replaced before the new fixtures could connect. Nothing on that list was a luxury. Each was a condition the garage already had.

The $180,000 project in our ADU cost guide that finished at $265,000 was a new detached unit replacing an old garage, not a conversion, but two of its three surprises, the $14,000 clay sewer reroute and the $6,000 to $8,000 panel upgrade, are exactly the ones a garage conversion faces. That is why we check the lateral and the panel on every site walk.

How to compare garage conversion quotes

Ask every bidder for the same six items in writing. The lowest quote has usually left two or three of them out.

1. Slab: what was assumed about the existing slab and moisture barrier, and what happens if it fails inspection.
2. Sewer: whether a camera inspection was done, and whether lateral repair or trenching is included or excluded.
3. Electrical: whether a 200-amp service upgrade is included, excluded or a change order, and who coordinates the utility.
4. Allowances: the dollar amount carried for cabinets, counters, tile, plumbing fixtures and appliances.
5. Envelope and code: Title 24 insulation, the framed-in door opening with matching stucco, the egress window, and fire separation on an attached garage.
6. Permits: who pulls them, whether fees are included, and whether the price assumes a standard plan that does not apply to a conversion.

Our ADU cost guide explains when a quote is simply too cheap and what a legitimate proposal should include. Read more on the garage conversion service page, or compare the route against a new unit on our ADU page.

Where we build garage conversions

We convert garages from our Van Nuys office across the San Fernando Valley, where 1950s to 1970s ranch houses with attached two-car garages are the classic candidate and permits run through LADBS; the rest of Los Angeles County, where Burbank, Glendale, Pasadena and Long Beach run their own building divisions; Orange County, where HOA architectural review often runs alongside the city permit; Ventura County; and western Riverside County, where larger lots make detached garages more common. Every city applies the same state ADU law with its own plan-check process. See all the areas we serve on our service areas page.

Garage conversion cost FAQs

How much does a garage conversion cost in Los Angeles?

A garage conversion ADU in Los Angeles typically costs $100,000 to $200,000, and most two-car garage conversions land between $98,000 and $150,000 including a kitchen, bathroom, insulation, electrical and plumbing. The top of the range is reached by detached garages that need utility trenching, sewer lateral repair, a 200-amp panel upgrade or upgraded finishes. These are typical Los Angeles budgeting ranges, not a quote.

Is converting a garage cheaper than building a detached ADU?

Yes, usually. A garage conversion in Los Angeles typically runs $100,000 to $200,000, while a detached new-construction ADU of 500 square feet runs $180,000 to $260,000 and larger units $230,000 to $550,000 depending on size. The conversion saves the foundation, framing, roof and the solar panels required on a new detached unit, but it still needs a full kitchen and bathroom, so it is never as cheap as finishing the garage as a room.

Do I have to replace the parking if I convert my garage into an ADU?

No. Under California Government Code section 66314, when a garage, carport or covered parking structure is converted to an ADU, the city cannot require the lost off-street parking spaces to be replaced. LADBS states the same rule for the City of Los Angeles. That removes what used to be the largest hidden cost of a garage conversion.

Does a garage conversion ADU need fire sprinklers?

A garage conversion ADU does not need fire sprinklers if sprinklers are not required for the main house, under Government Code sections 66314 and 66323. Most existing single-family homes in Los Angeles are not sprinklered, so most conversions are exempt. If the primary residence has a sprinkler system, the ADU will need one and it should be in the budget.

Can I use the Los Angeles pre-approved ADU standard plans for a garage conversion?

No. The LADBS ADU Standard Plan Program pre-approves complete designs for new detached units, from about 200 square foot studios to 1,200 square foot three-bedroom plans, and a garage conversion works within the structure you already have. A conversion goes through regular plan check with its own drawings, and under state law the agency must approve or deny a complete application within 60 days.

How long does a garage conversion take in Los Angeles?

A garage conversion ADU in Los Angeles usually finishes at the shorter end of our published six-month to one-year ADU timeline, because there is no foundation or framing phase. Plan check is capped at 60 days from a complete application under state law, and construction typically takes three to five months. The most common delays are a sewer lateral that needs repair and a 200-amp service upgrade, which added about three weeks on a project we have written about.

Get a written garage conversion price for your house

We will walk the garage, camera the sewer lateral, check the panel and the slab, and give you an itemized proposal that lists allowances, exclusions and the permit path for your city. The site visit and the estimate are free.

Homeowners are often shocked when they receive multiple ADU estimates and discover that the prices are tens of thousands of dollars apart.

One contractor may quote $120,000, another may quote $155,000, and a third may come in closer to $190,000. On paper, each contractor appears to be pricing the same ADU, using the same plans, square footage, and basic layout.

So why can the numbers be so different?

In our experience, the answer usually is not that one contractor is simply inexpensive while another is overpriced. The real issue is that the contractors may not actually be pricing the same scope of work, even when the proposals make it look that way.

One contractor may be pricing what the homeowner requested. Another may be pricing what the property and project will realistically require. Those are not always the same thing.

The lowest quote may also leave out important expenses that will eventually appear as allowances, exclusions, upgrades, or change orders after construction begins.

Understanding what is behind each number is far more important than comparing the totals at the bottom of the page.

The Same ADU Plans Can Produce Very Different Scopes

ADU plans show what is supposed to be built. They do not always show everything required to build it successfully on a specific property.

Plans may show the location of the kitchen, bathroom, bedroom, windows, doors, and electrical fixtures. However, they may not fully reveal the condition of the existing electrical panel, sewer lateral, soil, foundation, utility connections, or access to the construction area.

This is where quotes begin to separate.

A contractor who thoroughly investigates the property may include costs that another contractor has not identified yet. The lower contractor may eventually discover the same issues, but by then, construction may already be underway.

Utility Connections Can Change the Entire Budget

Utility work is one of the biggest reasons ADU quotes vary.

A detached ADU that can connect to an existing electrical, water, and sewer system may cost significantly less than one that requires:

• A new or upgraded electrical panel
• A longer electrical run to the backyard
• A new water service or larger water line
• A new sewer lateral
• Trenching through concrete or landscaping
• Utility company coordination
• Additional meters or service upgrades

Two contractors may both include a line called “utility connections,” but that does not mean they included the same work.

One contractor may assume the ADU can connect directly to the existing services. Another may have opened the electrical panel, reviewed the property layout, considered the distance to the sewer connection, and included realistic costs for upgrades.

The difference can easily reach tens of thousands of dollars.

Foundation and Soil Conditions Matter

For a detached ADU, the conditions below the ground can be just as important as the structure above it.

Soil conditions may affect the foundation design, excavation, drainage, footings, and structural engineering requirements. A contractor familiar with the neighborhood may already know that certain properties commonly require additional foundation work.

Another contractor may assume standard conditions without investigating further.

Both bids may say “foundation included,” but one may include additional excavation, reinforcement, engineering, or deeper footings while the other includes only a basic slab.

The wording may look similar. The actual construction being priced may be completely different.

Site Access and Construction Logistics Affect Labor

Site access is another cost factor that is easy to overlook.

Homeowners may see an open backyard and assume the project will be easy to access. Contractors must look at the entire construction sequence.

Questions that affect the price include:

• Can excavation equipment reach the backyard?
• Is there enough side-yard clearance?
• Will materials need to be carried by hand?
• Will concrete need to be pumped over the house?
• Are there fences, retaining walls, trees, pools, or landscaping in the way?
• Will temporary protection be required?
• Is street parking available for deliveries and workers?
• Will part of the property need to be demolished and restored for access?

When heavy equipment cannot reach the work area, labor costs increase. Material handling becomes slower, excavation becomes more difficult, and debris removal requires additional time.

A contractor who thinks through these details may appear more expensive than one who priced the project using only square footage.

ADU Allowances Can Hide Major Price Differences

Allowances are one of the most common reasons a proposal looks affordable in the beginning and becomes much more expensive later.

An allowance is a budget placeholder for an item that has not been selected or completely priced yet. Allowances are common for flooring, cabinets, countertops, tile, plumbing fixtures, appliances, lighting, and other finish materials.

Allowances are not automatically a problem. The problem is when they are too low, vaguely described, or misunderstood.

For example, two bids may both include a line that says:

“Kitchen allowance: $15,000.”

However, one contractor may have based that amount on actual cabinet, countertop, fixture, and installation costs. The other may have inserted a general placeholder that is unlikely to cover the kitchen the homeowner expects.

Once the homeowner selects real products, the difference becomes a change order.

Questions to Ask About Every Allowance

Homeowners should ask:

• Is the allowance based on products we have already discussed?
• Does it include materials, labor, delivery, taxes, and installation?
• What finish level does the allowance realistically cover?
• What happens when the selected products exceed the allowance?
• Is the difference billed at cost or with an additional contractor markup?
• Are there change order or administrative fees?
• Will we receive documentation showing the actual material cost?

A low allowance does not make the contractor less expensive. It may only delay part of the cost until later.

Some Contractors Include Risk While Others Defer It

Construction always involves a certain amount of uncertainty, especially when converting an existing structure or building on an older property.

Some contractors include a reasonable contingency in their estimate. Others leave contingency out entirely so the total appears lower.

A contingency is not extra money added without purpose. It is a budget for conditions that cannot be fully confirmed before demolition, excavation, testing, or inspection.

Common ADU surprises include:

• Deteriorated underground piping
• Insufficient electrical capacity
• Unforeseen foundation conditions
• Water damage
• Dry rot
• Termite damage
• Unpermitted existing work
• Framing that does not meet current requirements
• Utility company requirements
• Additional engineering requested during plan review

A quote with no contingency may look attractive, but the risk has not disappeared. It has simply not been priced yet.

The homeowner may still pay for it later through change orders.

A Real Garage Conversion That Increased by About 40%

One project that illustrates this involved converting an existing detached two-car garage into an approximately 400-square-foot, one-bedroom ADU.

The client wanted a kitchen, bathroom, bedroom, laundry area, and independent living space.

Garage conversions are often presented as the least expensive ADU option. The reasoning sounds simple: the slab and four walls already exist, so much of the construction is already complete.

Unfortunately, an existing garage was not necessarily built to function as habitable living space.

Based on the plans and an initial phone discussion, the early estimated range was approximately $85,000 to $95,000.

That changed after the site inspection.

What a garage conversion ADU involves, and what we inspect before quoting one, is on our garage conversion page.

The Existing Slab Did Not Have a Moisture Barrier

The garage slab did not have a proper moisture barrier below it.

This is common in older garages because the space was originally intended for vehicles and storage, not bedrooms and living areas.

Once the garage becomes habitable space, moisture protection becomes a serious issue. Without the proper system, moisture can travel through the slab and affect flooring, finishes, indoor comfort, and long-term durability.

Addressing the condition required additional preparation, materials, labor, and concrete-related work.

This was not an optional cosmetic upgrade. It was part of converting the garage responsibly into living space.

The Electrical Panel Was Not Large Enough

The existing home had an original 100-amp electrical panel that was already carrying much of the main house’s electrical demand.

Adding an ADU with a kitchen, laundry appliances, lighting, outlets, and a separate heating and cooling system required a full electrical load calculation.

The existing panel did not have enough capacity.

The project therefore required an upgrade to a 200-amp panel, along with additional permitting, inspections, coordination, labor, and material costs.

That expense was not obvious from the floor plan. It became clear only after the panel was opened and properly evaluated.

Our electrical page covers when a panel upgrade is required for an ADU and how it is permitted.

The Sewer Line Had Root Intrusion and Damage

The ADU required a new bathroom and kitchen, which meant connecting additional fixtures to the existing sewer system.

Because the property was older, we recommended performing a sewer camera inspection before finalizing the construction cost.

The inspection identified root intrusion and bellying in part of the existing line between the home and the street.

Connecting new fixtures to a damaged sewer line would have created a major risk. A portion of the line needed to be replaced before the ADU connection could be completed.

By the time the slab, electrical panel, and sewer conditions were included, the estimated project cost increased to approximately $130,000.

That was roughly a 40% increase from the original preliminary range.

None of these conditions were visible from the plans or a phone conversation. They were discovered through an in-person inspection, testing, and hands-on evaluation.

The plans showed what the client wanted. The property showed what it would actually take to build it.

Vague Proposal Language Often Leads to Change Orders

The language inside an ADU proposal matters just as much as the price.

A detailed proposal may look longer and more complicated than a one-page estimate, but specificity usually protects both the homeowner and the contractor.

Vague language creates room for disagreement.

Be Careful With “Standard Finishes”

The phrase “standard finishes” is open to interpretation.

Standard according to which contractor, supplier, manufacturer, or homeowner?

Instead of accepting a general description, ask for:

• Product names
• Model numbers
• Material specifications
• Price-per-square-foot allowances
• Cabinet construction details
• Countertop material
• Flooring thickness and quality
• Plumbing fixture brands
• Appliance allowances

The more specific the proposal is, the easier it becomes to understand what the price actually includes.

Watch for “As Needed”

Phrases such as “framing repairs as needed” or “electrical upgrades as needed” should lead to more questions.

What conditions would trigger the additional work?

How will the cost be calculated?

Will the homeowner receive written pricing before the work begins?

Is any portion already included in the contract?

“As needed” may be reasonable when a condition truly cannot be confirmed in advance, but the proposal should still explain the process for handling it.

Question Major Items Marked “TBD”

“TBD,” or “to be determined,” is especially concerning when it appears next to structural, plumbing, utility, foundation, or electrical work.

Sometimes additional information is genuinely required before a final number can be provided. However, the contractor should clearly explain:

• Why the amount cannot be determined
• What investigation is still needed
• Who is responsible for obtaining the information
• When the cost will be finalized
• Whether the amount is included in the total project budget

A proposal should not appear complete while major cost categories remain unresolved.

Exclusions Are Where ADU Costs Often Hide

Every proposal includes exclusions. No contractor can reasonably include unlimited responsibility for every possible condition.

However, exclusions must be reviewed carefully.

Important exclusions may include:

• Utility upgrades
• Electrical panel replacement
• Sewer lateral repairs
• Water main upsizing
• Permit fees
• Planning fees
• School or impact fees
• Engineering
• Surveying
• Soil reports
• Demolition
• Hazardous material testing or removal
• Landscaping restoration
• Fencing
• Appliance installation
• Utility company charges
• Unforeseen conditions

An exclusion does not necessarily make a proposal dishonest. It does mean the homeowner may need to budget for that item separately.

The question is not simply, “Is this excluded?”

The better question is, “How likely is it that our project will require this, and what could it cost?”

Contractor Overhead and Insurance Affect the Quote

A properly operated construction company has real business expenses.

These may include:

• General liability insurance
• Workers’ compensation coverage
• Contractor licensing
• Office and administrative staff
• Project management
• Supervision
• Accounting
• Scheduling
• Vehicles
• Equipment
• Safety programs
• Warranty service
• Permit coordination
• Quality control

A contractor who carries the correct insurance, uses qualified crews, provides supervision, and maintains a legitimate business structure will generally cost more to operate than someone working with minimal overhead.

That does not mean the largest company is automatically the best contractor. It does mean homeowners should understand that part of the price difference may represent risk management, staffing, organization, and accountability.

A lower quote from an uninsured or improperly licensed contractor is not necessarily a savings. It may transfer significant legal and financial risk to the homeowner.

Permit and Code Assumptions Can Create Large Gaps

ADU requirements can vary by city, county, fire district, utility provider, and property condition.

Requirements may also change over time.

Potential cost factors include:

• Fire access
• Fire-rated construction
• Utility separation
• Energy requirements
• Structural engineering
• Setbacks
• Height restrictions
• Addressing requirements
• Parking rules
• Stormwater management
• Sprinkler requirements
• Utility company upgrades
• Planning corrections
• Building department corrections

If one contractor has verified current requirements with the appropriate agencies and another is relying on general assumptions, their quotes may be far apart.

The lower number may not be wrong yet. It may simply be incomplete.

When a Higher ADU Quote May Be Worth Paying

A higher quote is not automatically better. The goal is not to select the most expensive contractor.

The goal is to identify which proposal is most likely to reflect the actual final cost and provide the most reliable path through construction.

The Higher Proposal Is More Specific

A higher quote may offer better value when it includes:

• Clearly defined materials
• Realistic allowances
• Labor and material breakdowns
• Site-specific utility work
• Permit responsibilities
• Engineering responsibilities
• A written change order process
• A detailed payment schedule
• Clear exclusions
• Realistic contingency planning

The price difference may represent the difference between a contractor who completed the necessary investigation and one who has not.

The Contractor Identified Conditions Others Missed

One of the strongest signs of value is when a contractor identifies an actual property condition that the others overlooked.

Examples include:

• An undersized electrical panel
• A deteriorated sewer line
• Poor site access
• Foundation concerns
• Insufficient water service
• Unpermitted existing construction
• Drainage problems

If the contractor can explain the condition, show evidence, and describe how it affects the project, the higher quote may simply be more complete.

The lower contractor may eventually reach the same price through change orders.

The Payment Schedule Is Based on Completed Work

A professional payment schedule should be connected to meaningful construction milestones.

Homeowners should be cautious when a contractor requests a large portion of the total contract before substantial work has been completed.

A clear milestone-based schedule helps the homeowner understand what work must occur before each payment becomes due.

Homeowners should also review their state’s home-improvement contract and deposit rules before signing.

The Contractor Can Explain the Price

A contractor who understands the project should be able to walk through the proposal line by line.

They should be able to explain:

• How utility costs were calculated
• Which conditions were confirmed
• Which costs are allowances
• Which costs are fixed
• What remains uncertain
• How change orders are handled
• What the contingency covers
• Why their proposal differs from others

A higher price with the same vague language and exclusions as the lower bid may simply be a higher markup.

A higher price supported by better investigation, stronger documentation, verified credentials, and clearer risk management may provide genuine value.

How to Compare Three ADU Quotes Fairly

Comparing the final totals alone is one of the least reliable ways to choose an ADU contractor.

A fair comparison requires putting each contractor on the same playing field.

Check each bid against our Los Angeles ADU budgeting ranges before you compare line items.

Standardize the Scope

Before comparing prices, provide every contractor with the same written scope.

The scope should identify:

• ADU size
• Number of bedrooms and bathrooms
• Attached, detached, or conversion type
• General finish level
• Appliance responsibilities
• HVAC expectations
• Flooring expectations
• Cabinet and countertop expectations
• Laundry requirements
• Utility assumptions
• Exterior work
• Landscaping or restoration responsibilities

Without a standardized scope, homeowners may be comparing three different projects that happen to use the same floor plan.

Compare Every Line Item

Place the proposals side by side and compare categories such as:

• Demolition
• Foundation
• Framing
• Roofing
• Windows and doors
• Electrical
• Plumbing
• Sewer
• HVAC
• Insulation
• Drywall
• Cabinets
• Countertops
• Flooring
• Tile
• Painting
• Fixtures
• Appliances
• Engineering
• Permits
• Utility upgrades
• Contingency
• Overhead and profit

Flag any category that is included in one proposal but missing, excluded, or vaguely described in another.

Pay special attention when one contractor includes a dollar amount and another simply writes “included.” Ask what “included” actually covers.

Interview Every Contractor Using the Same Questions

Ask all contractors the same questions so their answers can be compared fairly.

Useful questions include:

• How did you calculate utility connection costs?
• Did you confirm the electrical panel capacity?
• Did you evaluate the sewer line?
• What site conditions did you inspect?
• What does the contingency cover?
• What is excluded from your price?
• How are change orders priced and approved?
• Who will supervise the project?
• Will employees or subcontractors perform the work?
• Who will be our daily point of contact?
• Can you provide references from similar ADU projects?
• What triggers each payment?
• Is labor included in every material allowance?
• Which parts of the proposal are still based on assumptions?

The quality of the answers may reveal more than the proposal itself.

Verify Licensing and Insurance Independently

Do not rely only on documents handed to you by the contractor.

Homeowners should independently:

• Verify that the contractor’s license is active
• Confirm that the license classification covers the work
• Review publicly available complaint or disciplinary information
• Request a current certificate of insurance
• Confirm coverage directly with the insurance provider when appropriate
• Ask whether workers’ compensation coverage applies to the crew

Verification takes time, but it can prevent serious problems later.

Call References and Ask Specific Questions

Do not ask only whether the previous client was happy.

Ask:

• Did the final cost match the original estimate?
• If the price increased, what caused it?
• Were change orders explained before the work was completed?
• Did the contractor stay close to the original timeline?
• How did the contractor communicate during delays?
• Was the jobsite kept organized?
• Were inspections handled properly?
• Was the punch list completed?
• Would you hire the contractor again?
• What do you wish you had asked before signing?

When possible, request references from projects similar in size and scope that were completed recently.

Compare Adjusted Totals

After reviewing the scope and interviewing each contractor, adjust the proposals so they cover the same work.

For example, if one proposal excludes an electrical panel upgrade that the property clearly needs, add a realistic panel allowance to that contractor’s total before comparing it with the others.

Do the same for missing permits, engineering, sewer work, finish materials, or utility upgrades.

This adjusted comparison often changes which proposal appears to be the least expensive.

Compare Price Against Risk

Once the bids have been adjusted, evaluate more than cost.

Consider:

• Proposal completeness
• Communication
• Site investigation
• Verified credentials
• Reference feedback
• Payment structure
• Project management
• Change order process
• Quality of answers
• Realistic scheduling
• Warranty and follow-through

Paying more may be reasonable when the contractor has reduced the homeowner’s financial and construction risk.

Saving money is still important. However, a lower initial estimate offers little value if the final cost becomes significantly higher through omitted work and repeated change orders.

Put Every Clarification in the Contract

Any clarification made during meetings, emails, site visits, or phone conversations should be added to the written contract.

This includes:

• Allowance amounts
• Product selections
• Utility assumptions
• Permit responsibilities
• Exclusions
• Payment milestones
• Change order procedures
• Completion responsibilities
• Site protection
• Cleanup
• Warranty terms

Verbal promises are difficult to enforce and easy to misunderstand.

Before signing, make sure the contract reflects the project that was actually discussed.

The Lowest ADU Quote Is Not Always the Lowest Final Cost

When ADU estimates vary dramatically, homeowners should not immediately assume that the lowest contractor is cutting corners or that the highest contractor is overcharging.

Instead, determine what each contractor investigated, included, assumed, and excluded.

The best question is not:

“Which contractor gave us the cheapest quote?”

The better question is:

“Which quote is closest to what this ADU will realistically cost when it is completely finished?”

A detailed proposal supported by a proper site inspection, realistic allowances, current code research, verified credentials, and clear risk planning may appear more expensive at the beginning.

However, it may be much closer to the actual final cost.

Price is only one column in a much larger comparison. Homeowners who compare totals without reviewing the scope are making their decision based on the number contractors have the greatest ability to manipulate.

A successful ADU project begins with a realistic scope, a transparent proposal, and a contractor who is willing to explain exactly what is—and is not—included.

Let’s grab a coffee and talk ADUs, because this is one of the questions we get asked constantly, and honestly, we think the internet does homeowners a disservice on this topic. If you are still working out what counts as an ADU in the first place, start with our guide to what an ADU is under California law.

Everyone wants a simple answer.

“How much does an ADU cost per square foot?”

The problem is that the per-square-foot number is often one of the most misleading ways to estimate an ADU project.

After working on ADU projects and walking properties with homeowners, we can tell you that two ADUs with the exact same square footage can have dramatically different final costs. One could sit on a flat lot with easy access and utilities five feet away. Another could be on a slope, behind a house with a three-foot-wide side yard, 80 feet from the electrical panel and sewer connection.

Those are not the same project, even if both ADUs are 600 square feet.

The honest answer is that the cost to build an ADU depends on the type of ADU, the property itself, existing utilities, site access, city requirements, finishes, and what we discover once construction begins.

But homeowners still need real numbers to start planning, so let’s talk honestly about what you should expect, what actually drives the cost, and how to avoid getting halfway through an ADU project only to realize your original budget was never realistic.

How Much Should You Realistically Budget for an ADU?

As a broad starting point, these are the general ranges I would give someone sitting across the table from me today:

• Garage conversion: approximately $100,000 to $200,000
• Attached ADU: approximately $150,000 to $300,000
• Detached new-construction ADU: approximately $180,000 to $550,000 depending on size

These are typical Los Angeles budgeting estimates, not a price list or a quote. Your project can come in lower or higher depending on the house, the scope and the finishes; the only real number is a written proposal after a site visit.

These are ballpark numbers, not quotes

More importantly, those numbers assume reasonably normal conditions. Once you add a difficult slope, tight access, long utility runs, expensive city requirements, structural complications, or high-end finishes, the cost can rise quickly.

That is why we always tell homeowners to get a real site walk before falling in love with a budget number they found online.

Why the Type of ADU Matters So Much

The first question I ask is simple: what kind of ADU are we talking about?

A garage conversion, an attached addition, and a detached backyard house are three very different construction projects.

Garage Conversions Are Usually the Least Expensive Option

A garage conversion is generally going to be your least expensive option because much of the structure already exists.

You may already have:

• A foundation
• Exterior walls
• A roof
• Framing
• Existing access to utilities

Instead of building an entire structure from scratch, you are primarily converting an existing space into a legal, habitable dwelling with insulation, electrical, plumbing, HVAC, a kitchen, a bathroom, windows, finishes, and all required code upgrades.

For a typical two-car garage converted into a studio or one-bedroom ADU with a full kitchen and bathroom, we would generally tell a homeowner to think somewhere around $100,000 to $200,000, assuming the garage is in decent structural condition, the finishes are mid-grade, and utility connections are reasonably accessible.

A detached garage may cost more to convert than an attached garage because utilities may need to be trenched across the property. Depending on the situation, that can increase the conversion cost significantly.

The mistake homeowners make is assuming a garage conversion is always just drywall, flooring, and paint.

Sometimes it is relatively straightforward.

Other times, we open walls and find undersized footings, dry rot, outdated wiring, structural problems, or other conditions that must be corrected before the space can legally and safely become a home.

Existing conditions are always the gamble with a conversion.

Attached ADUs Usually Fall Somewhere in the Middle

For an attached ADU, we would generally tell someone to plan somewhere around $150,000 to $300,000.

The range is wide because an attached ADU could mean many different things. You may be converting existing square footage, adding a bump-out, sharing an existing wall with the main house, extending the roofline, or building a substantial addition.

The more of the existing house you can legally and practically use, the more opportunities there may be to control costs.

But once you start adding significant new foundation, framing, roofing, electrical service, plumbing, and structural work, the price begins moving closer to new construction.

Detached New Construction Is Usually the Most Expensive

A detached ADU is essentially a small standalone house.

You need a foundation. You need framing. You need a roof. You need exterior finishes, insulation, electrical, plumbing, HVAC, a kitchen, a bathroom, windows, doors, utilities, and everything else required for a complete residential structure.

For a fully built and permitted detached ADU, we would tell homeowners to realistically think somewhere around $180,000 to $550,000 depending on size.

A flat property with easy equipment access and utilities nearby may land closer to the lower end.

A sloped lot with tight access, long utility runs, retaining walls, difficult excavation, or premium finishes can land at the higher end or go well beyond it.

Even the excavation, concrete formwork, and foundation can represent a substantial expense before the house itself starts rising out of the ground.

Stop Focusing Only on Price Per Square Foot

One of the biggest misunderstandings we see is homeowners anchoring themselves to a number they saw online.

Someone reads that ADUs cost $300 per square foot and immediately starts doing math.

Six hundred square feet times $300 equals $180,000.

Done.

Except construction does not really work that way.

That $300-per-square-foot figure may assume:

• Flat land
• Easy equipment access
• Utilities nearby
• A standard foundation
• No major electrical upgrades
• No retaining walls
• No unusual city fees
• Builder-grade or mid-range finishes

Add a slope, a long sewer run, difficult access, upgraded finishes, or a major electrical service upgrade, and the price can climb quickly.

We have seen conditions that can push a project’s cost 40% to 60% above the simple number a homeowner originally pulled from the internet.

It is not necessarily that anyone lied to them. It is that ADU pricing is incredibly site-specific.

Smaller Does Not Always Mean Proportionally Cheaper

This surprises people.

A small 400-square-foot studio can cost more per square foot than an 800-square-foot one-bedroom.

Why?

Because both still need many of the same expensive components:

• A full kitchen
• A bathroom
• A water heater
• Electrical service
• Plumbing connections
• Sewer connections
• HVAC
• Permits
• Design and engineering
• Appliances and fixtures

Those costs do not disappear just because the living room is smaller.

A kitchen in a 400-square-foot ADU may cost almost as much as a kitchen in an 800-square-foot ADU.

The same applies to the bathroom.

That is why cost per square foot generally becomes more efficient as the unit gets larger. Your total construction cost is still higher, but certain fixed costs are being spread over more square footage.

Utility Connections Are the Silent Budget Killer

This is one of the biggest things homeowners overlook.

When we walk a property, we want to know exactly where the electrical panel, water meter, sewer cleanout, and proposed ADU location are.

If your new ADU sits 80 feet away from the main electrical panel and sewer connection, we may need to trench that entire distance.

Now we want to know what is between point A and point B.

Are there sprinkler lines?

Tree roots?

Existing concrete?

Pavers?

An old sewer line?

Mature landscaping?

A pool?

Anything we have to remove, work around, repair, or restore costs money.

In some cities, additional water, sewer, or utility requirements can add even more cost.

We have worked on projects where utility work became one of the biggest expenses on the entire job.

That is why we call utilities the silent budget killer. Most homeowners are thinking about cabinets, flooring, and countertops. Meanwhile, one of the most expensive parts of the project could be buried underground where nobody can see it.

Kitchens and Bathrooms Drive Cost More Than Most People Realize

A 500-square-foot studio with a complete kitchen and bathroom can have a surprisingly high cost per square foot.

Cabinets do not become cheaper because the ADU is small.

Neither do:

• Plumbing fixtures
• Shower waterproofing
• Tile installation
• Electrical circuits
• Ventilation
• Countertops
• Appliances
• Drainage
• Hot and cold water lines

Adding a second bathroom can significantly change a budget because, in many ways, you are adding another miniature construction project inside the larger one.

This is one of the reasons we caution homeowners against assuming square footage alone determines price.

Site Access Can Turn a Simple Project Into an Expensive One

When we visit a property, we do not just look at where the ADU will go.

We look at how we are going to build it.

Can we get a mini excavator into the backyard?

Can materials be delivered close to the construction area?

How wide is the side yard?

Is there a gate?

Are there mature trees or landscaping blocking access?

If machinery can access the site, great.

If everything has to be hand-dug and hand-carried through a three-foot-wide side yard, now I am paying for labor hours instead of machine hours.

That difference can add up fast.

A homeowner may look at an empty backyard and think, “There is plenty of room.”

We are looking at the path between the street and that backyard and asking how every piece of lumber, every bag of material, every piece of equipment, and every load of excavated soil is getting in and out.

Sloped Lots Can Dramatically Change the Budget

We always pay attention to grade.

Even a few feet of elevation change across the proposed building footprint can change the foundation design.

Instead of a straightforward slab, we may be looking at deeper footings, an engineered foundation, retaining walls, additional drainage, or significantly more excavation.

Depending on the severity of the property, slope-related work can add tens of thousands of dollars. In difficult situations, additional foundation or site work can reach $30,000 to $80,000 or more.

The backyard may look beautiful, but the lot can fight you.

That is why an in-person site visit matters so much.

A Real ADU Project That Went From $180,000 to $265,000

One project sticks with us because it is such a perfect example of how ADU budgets change.

The homeowners wanted to build a new detached ADU where an old, deteriorated garage had previously stood. They had already removed the garage and planned a roughly 600-square-foot, one-bedroom, one-bathroom ADU.

The homeowner had done her homework.

She researched online, spoke with a friend who had built an ADU, and came into the project expecting to spend approximately $180,000.

On paper, that did not sound unreasonable.

The final cost came in closer to $265,000.

It was not caused by one dramatic disaster. It was a combination of three completely different things.

Surprise Number One: The Sewer Line

When we started digging for the new foundation, we discovered an old clay sewer line from the main house running almost directly underneath where the new ADU was supposed to sit.

The pipe was decades old and had cracking and root intrusion.

Before we could pour the new foundation, the main house sewer line had to be rerouted around the proposed ADU.

That unexpected work added approximately $14,000.

It had nothing to do with upgrading the ADU or changing the design. It was simply an old underground condition nobody could see from the surface.

Surprise Number Two: The Electrical Panel

The main house had an original 100-amp electrical panel that was already fully loaded.

The homeowner wanted an electric range and heat pump for the ADU, so there simply was not enough electrical capacity to properly support the additional dwelling.

The property needed to be upgraded to a 200-amp panel.

That was not just a matter of changing out a box. It involved permitting, inspections, coordination with the utility company, and schedule delays.

The upgrade added approximately $6,000 to $8,000 and around three weeks of delay while waiting on the utility company’s timeline.

Surprise Number Three: The Homeowner Upgraded the Finishes

This happens more often than people think.

Once the framing was complete and the homeowner could physically walk through the rooms, the ADU became real.

What had originally been planned as a relatively basic unit was now going to become her mother’s full-time home.

The builder-grade selections no longer felt right.

She upgraded the tile package. She chose solid-surface countertops instead of laminate. She selected better cabinetry and upgraded the HVAC system.

Each decision felt small in the moment.

Together, those upgrades added approximately $30,000 beyond the original finish allowance.

The lesson we took from that project is something we now tell homeowners regularly:

Budget for what you cannot see, and budget for who you will become halfway through the project.

The sewer line was impossible to see from the surface.

The electrical panel was an infrastructure limitation.

The finish upgrades were a normal, human decision made when a drawing on paper became someone’s future home.

All three were real.

And all three cost money.

Why We Recommend a 15% to 20% Contingency

We tell homeowners to take their accepted ADU bid and have another 15% to 20% available as a true contingency fund.

Not money you hope to find later.

Not an available credit card.

Not money you are counting on receiving six months from now.

Actually have it available before the first major construction payment goes out.

For a straightforward new build on a flat, accessible lot with good information about the property, 15% may be reasonable.

For an older home, garage conversion, or property with unknown conditions, I lean closer to 20%.

Hidden conditions live behind walls and underground.

You may find:

• Dry rot
• Outdated electrical wiring
• Damaged sewer lines
• Undersized footings
• Structural deficiencies
• Tree roots
• Plumbing problems
• Unforeseen soil conditions

And then there are the changes homeowners voluntarily make after construction begins.

Different tile.

Better cabinetry.

Upgraded countertops.

Additional lighting.

A nicer HVAC system.

One upgrade may not break the budget. Ten of them can.

The First Thing We Check Is the City, Not the Property

Before we even drive to a property, we start by looking at the local requirements.

We want to understand:

• Maximum ADU size
• Height limits
• Setback requirements
• Parking rules
• Local ADU ordinances
• Potential owner-occupancy requirements, where applicable
• Any city-specific limitations or processes

State law has made ADU development easier in many ways, but local requirements and property-specific conditions still matter.

We have seen homeowners fall in love with a 1,000-square-foot ADU they found online, only to discover their actual property realistically supports something much smaller once setbacks, easements, existing structures, and site limitations are considered.

That is why we tell homeowners not to emotionally commit to a floor plan before they understand their property.

Most of our ADU work is inside the City of Los Angeles; the rules, the permit office and the typical lot conditions are covered on our page about building an ADU in the San Fernando Valley.

What We Look for During an ADU Site Walk

Once we visit the property, we are trying to answer one question:

Is this an easy site, or is this lot going to fight us?

The full list of what our ADU construction service includes is on the ADU page.

Setbacks and Buildable Area

Where can the ADU legally go after accounting for setbacks, easements, existing structures, and other restrictions?

The most obvious location is not always a legal building area.

Slope and Grade

Is the proposed building pad flat?

How much elevation change exists across the footprint?

Are retaining walls, additional engineering, drainage, or a specialized foundation likely to be required?

Construction Access

Can equipment actually reach the site?

How wide is the side yard?

Can materials be delivered efficiently?

Will excavation be completed with machinery or by hand?

Existing Utilities

Where are the:

• Water meter
• Sewer cleanout
• Electrical panel
• Proposed utility connection points

How far are they from the future ADU?

What lies between them?

Electrical Capacity

We want to know the amperage of the existing electrical service and whether the panel has the capacity to support another dwelling.

A fully loaded 100-amp panel is an immediate sign that an upgrade may be needed.

Parking

Depending on the jurisdiction and property conditions, parking requirements may still need to be reviewed.

Never assume. Verify.

Trees and Easements

Protected trees and utility easements can quietly eliminate what appears to be the perfect building location.

These are exactly the types of issues homeowners want to discover before paying for a complete design.

The Biggest Mistakes Homeowners Make Before Building an ADU

We see the same mistakes repeatedly.

Falling in Love With a Floor Plan Before Checking the Property

Someone finds a beautiful two-bedroom ADU online and becomes emotionally attached to it before confirming whether the lot can actually accommodate that size and layout.

Design for the property you have, not the Pinterest photo you found.

Not Researching City Requirements First

Before spending significant money on design, understand what the city will allow.

A little research early can prevent expensive redesigns later.

Assuming the Existing Utilities Can Handle Another Home

The fact that your electrical, sewer, water, or septic system works perfectly for your existing house does not automatically mean it can support another dwelling.

ADUs add real demand to existing infrastructure.

Find out what you are working with early.

Forgetting Soft Costs

Many homeowners create a construction budget but forget about:

• Architectural design
• Structural engineering
• Energy compliance
• Surveys
• Permit fees
• Utility fees
• Additional city charges

These costs are part of the project whether or not a hammer has touched the property yet.

Not Planning for Future Upgrades

Homeowners frequently upgrade materials once the rooms become real.

It is much easier to choose finishes thoughtfully before construction than to make emotional upgrade decisions halfway through the job.

We now encourage homeowners to take finish selections seriously early in the planning process so the “I love this” moment happens on paper or in a showroom instead of during framing, when saying no becomes much harder.

When Is an ADU Quote Too Cheap?

If someone quotes a detached, new-construction ADU with a complete kitchen and bathroom for under $100,000, we become very skeptical.

That does not automatically mean the contractor is dishonest.

But we want to know exactly what is included.

There is a real baseline cost to site work, foundation, utilities, framing, roofing, electrical, plumbing, a kitchen, a bathroom, HVAC, finishes, permits, and all the other work required to build a legal home.

Very low quotes usually deserve a much closer look.

Ask What Is Not Included

Some low advertised prices are for a shell only.

The number may include the basic structure, framing, and roof while excluding:

• Kitchen
• Bathroom fixtures
• HVAC
• Utility connections
• Permit fees
• Site work
• Landscaping restoration
• Finish upgrades

A low number is meaningless until you know where the contractor’s responsibility ends.

Ask About Permits and Fees by Name

Do not accept a vague statement like “permits included” without asking what that actually means.

Does it include the contractor’s labor to process permits?

Does it include actual city fees?

What about utility fees, school fees, or other jurisdiction-specific charges?

Those are very different things.

Ask Who Is Responsible for Plans and Engineering

Is architectural design included?

What about structural engineering?

Energy calculations?

Are the plans already complete, or is the contractor pricing from a rough concept that has not yet been engineered?

A price based on preliminary drawings can move considerably once engineering is complete.

Ask How Unforeseen Conditions Are Handled

If a contractor tells you nothing unexpected will happen, that concerns me more than a contractor who honestly explains the risks.

The question is not whether anyone can guarantee the absence of unforeseen conditions.

They cannot.

The question is how those conditions will be documented, priced, approved, and handled if they occur.

Why Three ADU Bids Can Be Tens of Thousands of Dollars Apart

When homeowners show me three wildly different proposals, my first move is not to compare the prices.

I compare the scope.

Nine times out of ten, three contractors are quietly pricing three different projects while all calling them an “800-square-foot ADU.”

One bid may be for a shell.

Another may include the shell and rough utility work.

The third may be a true turnkey proposal.

Once you normalize all three bids to the same actual scope, the difference often becomes much smaller.

Sometimes the cheapest proposal is no longer the cheapest at all.

What Should Be Included in a Legitimate ADU Proposal?

We want to see a real scope of work.

Not:

“Build 800-square-foot ADU: $220,000.”

I want enough detail to understand what is actually being built.

At a minimum, I want clarity regarding:

• Site preparation
• Excavation
• Foundation
• Framing
• Roofing
• Exterior finishes
• Windows and doors
• Electrical
• Plumbing
• HVAC
• Insulation
• Drywall
• Interior finishes
• Cabinets
• Countertops
• Flooring
• Fixtures
• Utility connections
• Permits and fees
• Landscaping or hardscape restoration

The proposal does not necessarily need to reveal every internal cost a contractor has, but the homeowner should clearly understand the scope.

Plans and Engineering Need to Be Clearly Defined

Who is responsible for architectural plans?

Who pays for structural engineering?

Is Title 24 or other required energy documentation included?

Has engineering actually been completed, or is the contractor pricing a conceptual design?

This matters enormously.

A preliminary number based on an unengineered sketch may change after the structural engineer specifies larger beams, deeper footings, retaining walls, or other requirements.

Utility Connections Should Be Spelled Out

This is one of the biggest areas where I see silent gaps between proposals.

One contractor may have physically measured a 70-foot trench run.

Another may have assumed utilities are nearby.

Those contractors are not bidding the same project.

Ask:

• How many feet of trenching are included?
• Where will electrical connect?
• Where will sewer connect?
• Where will water connect?
• Is panel work included?
• Who restores the areas disturbed during trenching?

The more specific the proposal, the fewer surprises later.

Finish Allowances Should Be Realistic

If a proposal includes an $8,000 flooring allowance, ask exactly what that buys.

What material?

What price per square foot?

Does it include installation?

Does it cover the entire ADU?

An allowance can look generous until you start making actual selections.

I have seen allowances set unrealistically low to make a proposal appear more competitive, knowing the homeowner will exceed them later through upgrades and change orders.

A cheap allowance does not make the project cheaper. Sometimes it only delays when you find out what the real price is.

HVAC Should Be Defined by System Type

“HVAC included” is not enough.

A basic wall heater is not the same thing as a mini-split heat pump.

A ductless mini-split is not the same as a fully ducted system.

Those systems have different equipment costs, installation requirements, energy implications, and comfort levels.

Know what you are actually getting.

Ask What Happens to Your Yard After Construction

Landscaping and hardscape restoration are forgotten constantly.

If we trench through your lawn, remove pavers, disturb irrigation, or run construction equipment across the property, what happens afterward?

Does the contractor restore it?

Is only rough grading included?

Are you responsible for hiring a landscaper?

That may not sound important while looking at floor plans, but it becomes very important when construction is finished and your new ADU looks great while the rest of the backyard still looks like a construction zone.

How I Read Three Very Different ADU Bids

If one bid is 25% to 30% lower than the others, we immediately want to understand why.

Possibilities include:

• Missing scope
• Unrealistically low allowances
• Major exclusions
• An underbid intended to win the job
• A plan to recover money through change orders

Even the honest version of underbidding can become a problem. A contractor who realizes halfway through the job that there is not enough money in the contract may begin struggling to pay subcontractors, cutting corners, delaying work, or taking on other jobs to create cash flow.

Cheap is not cheap if the project cannot be completed properly.

If one contractor is dramatically more expensive than everyone else, ask why.

Sometimes there is a legitimate reason. A more established company may have more staff, stronger project management, better insurance, more experienced subcontractors, and higher overhead.

Sometimes a contractor simply does not really want the project and prices it high enough that they are happy either way.

Ask them to walk you through the difference.

A contractor who understands and believes in their number should be able to explain what is driving it.

And remember: the middle bid is not automatically the right bid.

Normalize the scope first.

Then compare the price.

How Much Money Should You Actually Have Before Starting an ADU?

Our honest advice is simple:

Take your accepted, apples-to-apples bid and add another 15% to 20%.

Have those funds truly available before construction begins.

On an older property or garage conversion, we lean toward the higher end because there is a greater chance of finding hidden conditions.

On a clean, straightforward, flat-lot new build, 15% may be sufficient.

But do not enter a major construction project with every available dollar already committed to the base contract.

Running out of money halfway through an ADU build is one of the worst situations a homeowner can face.

This is not like delaying new cabinet hardware in a kitchen remodel.

A half-built ADU may mean:

• An exposed foundation
• Unfinished framing sitting through bad weather
• Expiring permits
• Subcontractors leaving for other projects
• Additional remobilization costs
• Delays that create even more expenses

It is much easier to have contingency money sitting untouched in savings than to scramble for financing when an unexpected problem is discovered in week six.

My Honest Advice Before You Build an ADU

Before you call contractors for bids, do three things.

First, look at your local ADU requirements and understand what may actually be allowed on your property.

Second, walk your own lot with a critical eye. Look at access, slope, the proposed building area, and the distance to your water, sewer, and electrical systems.

Third, look at your electrical panel and understand what you are working with.

Those three steps alone will put you ahead of many homeowners who begin the process with nothing more than a floor plan they love and a price-per-square-foot number they found online.

And before you sign a contract, compare scope before price.

Understand exactly what is included, what is excluded, how finishes are handled, who is responsible for plans and engineering, whether utility connections have been properly evaluated, and how unforeseen conditions and change orders will be handled.

The honest answer to “How much does it cost to build an ADU?” is not one universal number.

A garage conversion on a structurally sound property is not the same project as a detached backyard ADU on a hillside.

A 400-square-foot studio with a complete kitchen and bathroom may have a higher cost per square foot than a larger unit.

A $200,000 proposal that excludes utilities, city fees, HVAC, and restoration may ultimately cost more than a $250,000 turnkey proposal.

The right budget starts with understanding the property, the scope, and the real conditions of the job.

So before you fall in love with a number from a website, get someone experienced to walk the site.

Because when it comes to ADUs, the question is not just, “How big do you want to build?”

The real question is, “What is this specific property going to require to build it correctly?”

Frequently Asked Questions