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.