ADUs in Unincorporated Los Angeles County: rules, requirements and what fits on your property
What state law allows on any property in unincorporated Los Angeles County, what the county adds, and what it costs to build. Updated November 6, 2026.
State rules now. The city's own rules are being added.
What state law allows in Unincorporated Los Angeles County
These apply in every California city and county. The county can allow more, never less. State rules current to November 6, 2026.
- Detached ADU
Up to 1,200 sq ft. At least 800 sq ft is always allowed.
- Height
16 ft; 18 ft within half a mile of transit, plus 2 ft for a roof that matches the home.
- Setbacks
4 ft from the side and back of the property.
- Parking
None needed within half a mile of transit, or for a conversion.
- Fees
No impact fees up to 750 sq ft. No school fees up to 500 sq ft.
- Timeline
The county must decide within 60 days of a complete application.
What Unincorporated Los Angeles County adds
From the county's zoning code and ADU handbook. These join reports when Unincorporated Los Angeles County is covered.
- Plans
- The county's own pre-approved plans, free to use: LA County plans.
- Homeowner associations
- HOAs can set reasonable rules but can’t ban ADUs (Civil Code 4751).
Questions about ADUs in Unincorporated Los Angeles County
Short answers from the state rules. Your address gives the answer for your property.
- Can I build an ADU in Unincorporated Los Angeles County?
- Yes. State law requires every California city and county, including unincorporated Los Angeles County, to allow at least one ADU on a property with a home, and a junior ADU inside the home. Most properties zoned for homes qualify. Unincorporated Los Angeles County can add its own limits but cannot go below the state minimums. Enter your address to see the rules for your property.
- How big can an ADU be in Unincorporated Los Angeles County?
- State law allows a detached ADU of up to 1,200 sq ft, and at least 800 sq ft is always allowed regardless of lot coverage. A junior ADU inside the home can be up to 500 sq ft. An attached ADU can be half the size of the home, and 800 sq ft is always allowed.
- What are the setback and height rules for an ADU in Unincorporated Los Angeles County?
- At least 4 ft from the side and back of the property. Height is 16 ft, or 18 ft within half a mile of major transit, plus 2 ft for a roof that matches the home. Unincorporated Los Angeles County can allow more.
- Do I need parking for an ADU in Unincorporated Los Angeles County?
- No parking is required within half a mile of major transit, for a garage conversion, or when parking is available on the street. When a garage is converted, no replacement parking is required.
- How much does an ADU cost in Unincorporated Los Angeles County?
- Build cost depends on size and the site. ADUCheck's range is $250 to $400 per sq ft for new construction and $100 to $200 per sq ft for a conversion, from the Terner Center ADU owner survey. City impact fees are waived up to 750 sq ft and school fees up to 500 sq ft.
- Does Unincorporated Los Angeles County have pre-approved ADU plans?
- Unincorporated Los Angeles County has not published its own program that ADUCheck has read. The City of Los Angeles standard plans and the LA County pre-approved plans are the nearest programs; any plan can also be submitted in unincorporated Los Angeles County as a custom plan.
- How long does an ADU permit take in Unincorporated Los Angeles County?
- State law gives the county 15 business days to say whether your application is complete and 60 days from a complete application to approve or deny it. A missed deadline counts as approval.