Author: Dekel Sofer

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 neighboring 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 in Los Angeles and ADU construction 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 pricing page 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 66311.5 (formerly 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 project. 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 catalog 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 neighbor 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 R313.1). 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 neighbor’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.

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. For a smaller unit inside the existing house, see our guide to junior ADU rules and cost in Los Angeles.

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 neighborhood; 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. If there is no garage to weigh and the real choice is a unit built onto the house, our comparison of an attached vs. detached ADU covers size limits, fire separation and solar.

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.

Answer a few questions in 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 catalog is available for detached units; see four ways to add an ADU in Los Angeles. 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; as our Corona ADU page explains, the attached garages and HOAs of Corona’s newer tracts change the calculus there. See all of our service areas.

Sources

ADU law changes most years and local ordinances are amended separately from the state statute. The rules referenced above were checked against the current state sources on the date shown; confirm anything decision-critical with LADBS or your city for your specific lot.

• California Department of Housing and Community Development, Housing Law Fact Sheets — Accessory Dwelling Units (April 2026) — confirms that ADU law sits at Government Code sections 66310–66342, the four-foot side and rear setback limit for new detached ADUs, the 60-day decision deadline, and that impact fees may not be charged on an ADU of 750 square feet or less or on a JADU.
• California HCD, Accessory Dwelling Unit Handbook (March 2026) — Government Code section 66321(b)(3) bars a city from applying lot coverage, floor area ratio, open space or minimum lot size standards that would not permit at least an 800 square foot ADU with four-foot side and rear setbacks, at a height of up to 16 feet.

Last reviewed 17 September 2026.

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 neighboring 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 in Los Angeles 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 neighbor 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. Answer a few questions in 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 gray 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.

If an addition is the direction, home addition ideas for a Los Angeles house walks through bump-outs, primary suites, family room expansions and partial and full second stories, with a cost range for each.

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 neighborhood 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 catalog 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; our Anaheim ADU page covers the Anaheim Hills case, where slope, a soils report and usually an HOA come together. Ventura County cities such as Thousand Oaks have their own building divisions and hillside lots that often need a soils report; in Thousand Oaks, whether the lot is flat and whether it sits in a fire zone decide most of an ADU’s cost, as our ADU page for Thousand Oaks explains. 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 project.

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 neighborhood; 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.

Sources

The ADU rules on this page are California statute, which the Legislature amends most years; local ordinances are updated separately and can lag it. Room additions are governed by ordinary zoning and building code instead, which varies by city. Confirm both before you choose between them.

• California HCD, Housing Law Fact Sheets — Accessory Dwelling Units — ADU law at Government Code sections 66310–66342: the 60-day decision deadline, four-foot side and rear setbacks, and no impact fees on an ADU of 750 sq ft or less.
• California HCD, Accessory Dwelling Unit Handbook (March 2026) — Government Code section 66321(b)(3), the rule that local standards may not prevent at least an 800 sq ft ADU with four-foot setbacks at up to 16 feet.
• LADBS, Building Permits — the work that requires a permit in the City of Los Angeles, and the rule that building plans must be approved as a Building Plan Check before a permit is issued.

Last reviewed 17 September 2026.

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 neighboring 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 pricing page 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; the largest items were 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 (see HUD’s Fair Market Rents); 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 neighborhood.
• 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 license, 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 neighboring 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 ADU page 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 neighbor 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. Our Thousand Oaks ADU page covers what slope does to a budget there.

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. In Irvine the village association usually sets the timeline, as our Irvine ADU page explains.

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 accounted for most of the move 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 catalog 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 catalog; our Los Angeles ADU contractor page lists each phase there with its typical duration. 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 two 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.

Sources

The statutory deadlines on this page come from California ADU law, which the Legislature amends most years; local ordinances are updated separately and can lag the state statute. The durations either side of those deadlines are our own, from projects we have built, not published figures. Confirm the current rules before you plan around a date.

• California HCD, Housing Law Fact Sheets — Accessory Dwelling Units — the 60-day decision deadline on a complete ADU application, the four-foot side and rear setbacks, and the rule that no impact fees may be charged on an ADU of 750 sq ft or less (Government Code section 66311.5, formerly 66324). ADU law sits at Government Code sections 66310–66342.
• LADBS, Standard Plan Program — the pre-approved plan route, which LADBS states “greatly reduces the time required for plan check.” ADUs are among the eligible project types.
• LADBS, Building Permits — what requires a permit and plan check in the City of Los Angeles, which is the step the 60-day clock runs against.

Last reviewed 17 September 2026.

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.