California ADU Rules Explained (2026)
What state law guarantees when you add an accessory dwelling unit or junior ADU in California: sizes, heights, setbacks, parking, fees and the 60-day approval.
California law sets a floor every city and county has to respect for accessory dwelling units (ADUs). On a single-family lot you can generally add one ADU and one junior ADU; cities must approve a qualifying application within 60 days, without a hearing; they must allow at least an 800 sq ft detached ADU with 4-foot side and rear setbacks; and they can't require you to live there.
What you can build
Government Code 66323 requires cities to approve these by right in residential and mixed-use zones:
- Single-family lot: one ADU or junior ADU inside the house or an existing accessory structure (with up to 150 sq ft of expansion for access), and one new detached ADU of up to 800 sq ft with 4-foot side and rear setbacks.
- Multifamily lot, conversions: ADUs in non-living space such as storage rooms, garages or attics: at least one, and up to 25% of the existing units.
- Multifamily lot, detached: up to 8 detached ADUs on a lot with an existing multifamily building (but no more than the number of existing units), or 2 with a proposed one.
Cities can allow more. They can't require you to fix nonconforming zoning conditions as a condition of approval.
Size
- A city's maximum size can't be less than 850 sq ft, or 1000 sq ft for an ADU with more than one bedroom.
- Whatever the local lot coverage, floor area or open space rules, an ADU of at least 800 sq ft with 4-foot setbacks must be allowed.
- The state definition tops out at 1,200 sq ft for a detached ADU.
- A junior ADU (JADU) is up to 500 sq ft within the existing house, with its own entrance and an efficiency kitchen; it may share a bathroom.
Height
| ADU type | Height cities must allow |
|---|---|
| Detached, single-family or multifamily lot | 16 ft |
| Detached, within ½ mile walk of a major transit stop or high-quality transit corridor | 18 ft, plus 2 ft (20 ft) to match the main home's roof pitch |
| Detached, on a lot with a multistory multifamily building | 18 ft |
| Attached to the main home | 25 ft or the zone's limit, whichever is lower (up to two stories) |
Setbacks and parking
Side and rear setbacks can't exceed 4 feet, and a city can't impose a front setback that would prevent an 800 sq ft ADU. Converting an existing garage or structure needs no new setback. Cities can't require parking for an ADU within half a mile walking distance of public transit, and can't require replacement parking when a garage is converted or demolished for an ADU.
Approval: 60 days, no hearing
A city or county must approve or deny a complete ADU permit application within 60 days (Gov. Code 66317). Review is ministerial: if the plans meet the objective standards, the permit issues, with no public hearing and no discretionary design review. If the city misses the deadline, the application is deemed approved. A denial must come with a full list of the defects and how to fix them.
Owner occupancy, rentals and sales
- No owner-occupancy requirement for ADUs (Gov. Code 66315). A JADU that shares a bathroom with the house does require the owner to live in the house or the JADU.
- Cities can require rentals of an ADU to be for 30 days or longer, which rules out short-term vacation rentals.
- An ADU generally can't be sold separately from the main home, with limited exceptions for nonprofit and qualifying condominium projects.
Fees and property tax
- Impact fees: none for an ADU under 750 sq ft. Larger ADUs can be charged in proportion to the main home's size. Utility connection fees follow separate rules.
- Property tax: building an ADU is new construction, so only the added value of the ADU is assessed and added to your existing Prop 13 value; the rest of the property isn't reassessed. Expect a supplemental bill when it's finished; see supplemental property tax bills.
Renting it out
An ADU tenant has the same rights as any other tenant. An owner who lives on the property and rents out no more than two units or bedrooms, including an ADU, is exempt from AB 1482's rent cap and just cause rules; see just cause eviction rules.
Check your project
The ADU Ministerial Approval Checker tests a design against the state floor. To weigh construction cost against rent, try the ADU Cost & Rent Income Estimator.
Frequently Asked Questions
How big can an ADU be in California?
Cities can set limits, but not below 850 square feet (1000 for more than one bedroom), and they must always allow an 800 sq ft ADU with 4-foot side and rear setbacks. A junior ADU can be up to 500 square feet inside the house.
How tall can a detached ADU be in California?
At least 16 feet anywhere. At least 18 feet within half a mile of major transit or on a lot with a multistory multifamily building, plus 2 more feet (20 total) to match the main house's roof pitch near transit. An attached ADU can be up to 25 feet or the zone's height limit, whichever is lower.
Do I have to live on the property to build an ADU?
No. Cities can't require the owner to live on the property for an ADU. The owner-occupancy rule only applies to a junior ADU that shares a bathroom with the house.
How long does a city have to approve an ADU?
60 days from a complete application. Approval is ministerial: no public hearing and no discretionary review for an ADU that meets the objective standards.
Are there impact fees on an ADU?
Not for an ADU under 750 square feet. Larger ADUs can be charged impact fees proportional to the main home's size.
This article is for general information only and is not legal advice. Local ordinances add their own objective standards; check with your city or county planning department. Sources: Government Code 66310-66342 (Chapter 13, Accessory Dwelling Units, as amended through SB 543, 2025), especially 66313, 66314, 66315, 66317, 66321 and 66323; California Department of Housing and Community Development ADU Handbook.