California ADU Laws

A California Accessory Dwelling Unit (ADU) is a self-contained second home on a residential lot, and a Junior ADU (JADU) is a small unit (up to 500 sq ft) carved out of an existing house. A series of state laws (Gov. Code §§ 66310 et seq., formerly §§ 65852.2 and 65852.22) require local governments to approve qualifying ADUs ministerially — "by right," with no public hearing or discretionary review — and override many restrictive local ordinances.

These rules are powerful but detailed: size, setbacks, parking and timelines are all set by state minimums that cities cannot undercut. Whether a particular lot qualifies — and what limits actually apply — is the kind of question GoCodebook answers with a citation, the same way it handles California rent and tenant laws.

State law guarantees an ADU of at least 850 sq ft (or 1,000 sq ft for units with two or more bedrooms) regardless of local floor-area or lot-coverage caps, and detached ADUs can run up to roughly 1,200 sq ft. Required side and rear setbacks are limited to 4 feet, and a city cannot impose front-setback rules that would block an otherwise compliant ADU under 800 sq ft.

On parking, local agencies cannot require a parking space when the ADU is within ½ mile of public transit, is part of the existing primary residence, or when a converted garage is replaced — and units under 500 sq ft are generally exempt. These minimums apply even where a local ordinance is stricter, which is why the controlling rule needs to be checked per jurisdiction.

Qualifying ADUs and JADUs must be reviewed ministerially within 60 days of a complete application — with no hearing — and on single-family lots a city must allow at least one internal ADU, one JADU, and one detached new-construction ADU. Multifamily properties can add detached ADUs as well (commonly up to one per existing unit, with further expansion under recent bills like SB 1211).

On owner-occupancy, the statewide bar on requiring owners to live on-site applied through prior years, and today an owner-occupancy requirement generally only applies to a JADU when it shares a bathroom with the main house. As with AB 1482 exemptions, the precise rule turns on unit type and local adoption — facts GoCodebook can confirm.

ADU law and SB 9 are different tools. ADU law adds an accessory unit (and a JADU) to an existing lot, while SB 9 lets eligible single-family owners split a lot and/or build a duplex. They can sometimes stack, but each has its own eligibility and size rules.

A defining feature of ADU law is preemption: where a local ordinance conflicts with the state minimums, the state standards control, and the Department of Housing and Community Development (HCD) can find noncompliant local rules void — so state ADU standards apply by default until a city adopts a compliant ordinance. Confirming which standard governs a specific address is exactly what GoCodebook is built for.