Figures below are planning ranges for Greater Los Angeles, intended to help you build a realistic budget. They are not a quote — every project is priced from its own site, scope, and selections.
Types of ADUs
California recognizes a few kinds of ADU. The right one depends on your lot, your budget, and how you plan to use the space.
- Detached ADU: a stand-alone unit in the backyard
- Attached ADU: new space added to the main house with its own entrance
- Garage conversion: an existing garage turned into a living unit
- Junior ADU (JADU): a smaller unit carved out of space inside the existing house
What an ADU costs in Los Angeles
An ADU or garage conversion in Greater Los Angeles commonly costs $150,000 to $400,000. Conversions sit at the lower end because the structure already exists. A new detached unit sits higher, because it needs its own foundation, roof, and utility connections.
Utility runs are the cost people miss most. A new sewer line, a separate electrical service, or a long trench across the yard can add a meaningful amount. We look at these on the first site visit.
California ADU rules, in plain language
State law makes ADUs easier to permit than most other projects. Cities must review a complete ADU application ministerially, which means against set standards rather than at a hearing. Local rules still apply, so details vary by address. These are the general state rules:
- Detached ADUs are commonly allowed up to 1,200 square feet
- A junior ADU can be up to 500 square feet, inside the existing home
- Side and rear setbacks for an ADU are generally 4 feet
- Impact fees are generally waived for ADUs under 750 square feet
- Parking is generally not required near public transit, and a converted garage generally does not have to be replaced
Permits in the City of Los Angeles
Inside the City of Los Angeles, ADU permits go through the Department of Building and Safety (LADBS). The city has also offered a standard plan program with pre-reviewed ADU designs, which can shorten plan check. Check the current program with LADBS, since the rules and options change.
Hillside lots, fire hazard zones, and the Coastal Zone add review steps. Outside the city, Los Angeles County and neighboring cities each have their own ADU rules within the state framework.
How long it takes
Construction on an ADU or garage conversion typically takes 5 to 10 months. Design and permitting come first. A conversion with a simple layout moves fastest. A new two-story detached unit on a sloped lot takes the longest.
Frequently asked questions
How much does an ADU cost in Los Angeles?
An ADU or garage conversion in Greater Los Angeles commonly costs $150,000 to $400,000. Garage conversions sit at the lower end because the structure already exists. New detached units cost more because they need their own foundation, roof, and utility connections.
How big can an ADU be in California?
State law commonly allows a detached ADU up to 1,200 square feet and a junior ADU up to 500 square feet inside the existing home. Local rules for height, setbacks, and lot coverage still apply, so the size you can build depends on your address.
Is a garage conversion cheaper than a new ADU?
Usually yes, because the foundation, walls, and roof already exist. Older garages sometimes need a new slab, added insulation, or structural upgrades to meet code for living space, so an inspection early on is worth it.
How long does it take to build an ADU?
Construction typically takes 5 to 10 months. Design and permitting add time before that. Conversions with simple layouts move fastest, while new detached units on sloped lots take the longest.
Do I need to provide parking for an ADU?
Often not. California generally waives ADU parking requirements near public transit, and a garage converted to an ADU generally does not have to be replaced. Check the rules for your specific address with your local building department.
