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California ADU law, explained
California's ADU law sets what every city must allow for a backyard home. Here is what it says, section by section, as our check reads it.
Not legal advice; confirm with the city.
Your city may allow more. A city can't be stricter than these rules. Where the state lets a city set a number inside its range, the table says so.
How big can my ADU be?
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What the law says
Each line cites its section on leginfo.legislature.ca.gov, the official code. Each was read there on 31 Oct 2026.
How big
| Section | What it says | Who sets the number |
|---|---|---|
| Gov. Code §66314(d)(5) | A detached ADU may be up to 1,200 sq ft. | The state |
| Gov. Code §66314(d)(4) | An attached ADU may be up to half the floor area of the existing home. A city can't use this to stop an 800 sq ft ADU. | The city, within the state's range |
| Gov. Code §66321(b)(3) | Lot coverage, floor area ratio, open space, front setback and minimum lot size rules can't stop an 800 sq ft ADU with 4 ft side and rear setbacks. | The state |
| Gov. Code §66323(a)(2)(A) | One new detached ADU with 4 ft side and rear setbacks must be approved. A city may cap that ADU at 800 sq ft. | The state |
| Gov. Code §66321(b)(2)(A) | A city's size limit can't be under 850 sq ft of interior livable space. | The state |
| Gov. Code §66321(b)(2)(B) | A city's size limit can't be under 1,000 sq ft for an ADU with more than 1 bedroom. | The state |
| Health and Safety Code §17958.1(a) | A city's minimum size can't ban an efficiency unit. A city may allow one from 150 sq ft. | The city, within the state's range |
| Gov. Code §66313(d) | A junior ADU is up to 500 sq ft, inside the existing home (an attached garage counts as part of it, §66333(d)). | The state |
Setbacks and height
| Section | What it says | Who sets the number |
|---|---|---|
| Gov. Code §66314(d)(7) | Side and rear setbacks of no more than 4 ft. None for a conversion of an existing space, or a rebuild in the same place and size. | The state |
| Gov. Code §66321(b)(4)(A) | A city must allow a detached ADU at least 16 ft high. | The city, within the state's range |
| Gov. Code §66321(b)(4)(B) | Within half a mile walk of a major transit stop or high-quality transit corridor: at least 18 ft, plus 2 ft to match the home's roof pitch. | The city, within the state's range |
| Gov. Code §66321(b)(4)(C) | On a lot with a multistory multifamily building: at least 18 ft. | The city, within the state's range |
| Gov. Code §66321(b)(4)(D) | An attached ADU: 25 ft or the zone's height for the home, whichever is lower. No more than 2 stories need be allowed. | The city, within the state's range |
Parking
| Section | What it says | Who sets the number |
|---|---|---|
| Gov. Code §66314(d)(10)(A) | Where a city asks for parking: at most 1 space per ADU or per bedroom, whichever is less. Tandem on a driveway counts. | The city, within the state's range |
| Gov. Code §66322(a) | No parking may be asked for within half a mile walk of public transit, in a historic district, inside the home or an accessory building, where street permits are not offered to the ADU, within a block of a car share, or when the ADU is filed with a new home. | The state |
| Gov. Code §66314(d)(11) | Parking lost when a garage or carport is pulled down or turned into an ADU doesn't have to be replaced. | The state |
Fees, fire sprinklers and the decision
| Section | What it says | Who sets the number |
|---|---|---|
| Gov. Code §66311.5(c)(1) | No impact fees for an ADU of 750 sq ft of interior livable space or less, or a junior ADU of 500 sq ft or less. Above that, in proportion to the home's floor area. | The state |
| Gov. Code §66314(d)(12) | Fire sprinklers aren't needed if the home doesn't need them. | The state |
| Gov. Code §66317(a)(3) | A city decides a complete application within 60 days, or it is deemed approved. | The state |
Owning and renting
| Section | What it says | Who sets the number |
|---|---|---|
| Gov. Code §66314(d)(1) | The ADU may be rented, but it stays on the same title as the home (with narrow exceptions in sections 66340 to 66342). | The state |
| Gov. Code §66323(e) | An ADU approved this way is rented for terms longer than 30 days. | The state |
| Gov. Code §66315 | A city can't ask that someone on the title live on the lot for an ADU. | The state |
| Gov. Code §66333(b) | For a junior ADU, someone on the title must live in the home or in the junior ADU only if the junior ADU shares a bathroom with the home. | The state |
Junior ADUs, and more than one ADU
| Section | What it says | Who sets the number |
|---|---|---|
| Gov. Code §66333(e)-(f) | A junior ADU always has its own separate entrance and an efficiency kitchen. It may share a bathroom with the home. | The state |
| Gov. Code §66333(e)(2) | A junior ADU without its own bathroom needs a separate entrance and an inside door to the main living area of the home. | The state |
| Gov. Code §66323(a) | On a single-family lot: an ADU and a junior ADU inside the home or an existing accessory building, and a new detached ADU, in any combination. | The state |
What our check can't see
- Planner check needed: we can't see whether the lot is in the coastal zone, a very high fire hazard severity zone or a historic district. Each can add rules.
- Planner check needed: a lot on a septic system may need the health department to agree.
- Planner check needed: the building code may set a gap between the ADU and the home. We draw about 10 ft.
- Planner check needed: SB 1117 may change impact fees above 750 sq ft. Its final status is unconfirmed.
Indicative: based on California's state ADU law. City ordinances can set some numbers differently.
Your city's own ADU rules
These are the city pages our check links to. Where we haven't opened a link ourselves, it says so.
- City of Sacramento, opened 31 Oct 2026
- Sacramento County. Planner check needed: we haven't opened this link.
- County of San Diego (unincorporated areas). Planner check needed: we haven't opened this link.
- City of San Jose. Planner check needed: the city refuses our fetcher.
- City of Los Angeles. Planner check needed: the city refuses our fetcher.
- California HCD. Planner check needed: HCD refuses our fetcher, so a person confirms this link.
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Not legal advice; confirm with the city.