California ADU law, in plain English

State ADU law was renumbered. It used to sit at Government Code section 65852.2 (and 65852.22 for JADUs), and a great deal of what is written online still cites those sections. It now lives at Government Code sections 66310 through 66342, with JADUs at 66333.

This matters when reading anything published before 2025: an article citing 65852.2 is not necessarily wrong, but it is old enough that its details should be re-checked. Three more sections were renumbered on January 1, 2026 — 66324, 66327, and 66332 became 66311.5, 66313.5, and 66311.7 — and 66333.5 was added.

Under current state law, most single-family lots in California can add at least one ADU, and many can add a detached ADU plus a JADU carved from the existing home. Multifamily properties have their own separate allowances, including up to eight detached ADUs on a lot with an existing multifamily building, capped at the number of existing units on the lot.

What a specific lot can actually take is a different question from what the ordinance permits. Setbacks, existing structures, utility locations, easements, and access all narrow it. That is what the site walk is for.

Three different numbers get quoted, and they mean different things.

850 / 1,000 square feet is the floor on a city's maximum. A city may set maximum ADU sizes by ordinance, but that maximum must allow at least 850 square feet of interior livable space, or at least 1,000 square feet for an ADU with more than one bedroom (Gov. Code, § 66321(b)(2)).

1,200 square feet is the state default for a new detached ADU where a city has no compliant ADU ordinance (Gov. Code, § 66314(d)(4)). It is a ceiling in that situation, not a universal entitlement — and a city is free to adopt a less restrictive rule that allows more (Gov. Code, § 66325(b)).

800 square feet is the size that lot coverage, floor area ratio, open space, and front setback requirements cannot be used to preclude, as long as the unit keeps four-foot rear and side setbacks (Gov. Code, § 66321(b)(3)).

Size is measured as interior livable space — the space intended for human habitation, including bedrooms, bathrooms, kitchens, laundry, closets, and interior stairs (Gov. Code, § 66313(e)).

An ADU created by converting existing space — part of the primary home, or an existing accessory structure such as a garage — is not subject to the unit size limits above (Gov. Code, § 66323(a)(1)). It is also exempt from local open space and landscaping requirements, and from parking requirements.

No setback is required for an ADU or JADU created inside an existing living area or accessory structure, or for an ADU built in a new structure in the same location and to the same dimensions as the structure it replaces (Gov. Code, § 66314(d)(7)).

A JADU is up to 500 square feet and must be created within the walls of the existing single-family home rather than built new. The permit path is generally simpler and the cost lower than a detached unit. JADUs are permitted ministerially, the same as ADUs.

A JADU may share sanitation facilities with the main house or have its own, and as of January 1, 2026 that choice decides whether an owner has to live on the property. Shared sanitation facilities means owner occupancy IS required. Separate sanitation facilities means it is NOT (Gov. Code, § 66333(b)). Anything written before 2026 saying a JADU always requires an owner on site is out of date.

A JADU also cannot be used as a short-term rental, and if rented must be rented for longer than 30 days (Gov. Code, § 66333(g)).

For ADUs: a local agency cannot impose an owner-occupancy requirement (Gov. Code, § 66315). The one exception is an ADU sold separately to a qualified buyer under Government Code section 66341(c)(3). The old sunset date on this prohibition was removed — no owner-occupancy requirement for ADUs is now the standing rule, not a temporary one.

For JADUs — this changed on January 1, 2026. Owner occupancy is required only if the JADU has shared sanitation facilities with the primary structure. If the JADU has its own separate sanitation facilities, owner occupancy is not required. It is also not required where the owner is a governmental agency, land trust, or housing organization. Where it does apply, the owner may live in either the remaining portion of the primary residence or in the JADU itself. (Gov. Code, § 66333(b), as amended by AB 1154, Chapter 507, Statutes of 2025.)

This is a genuine reversal of the older rule that a JADU always required an owner on site, and most material published before 2026 still states the old version. Flag that when a visitor has read otherwise.

A local agency may require that an ADU or JADU be rented for terms longer than 30 days (Gov. Code, §§ 66315; 66323(e); 66333(g)). In practice that means short-term vacation rental is commonly off the table.

For JADUs specifically, this is no longer merely something a city may do: as of January 1, 2026, a JADU cannot be used as a short-term rental, and if rented must be rented for longer than 30 days (Gov. Code, § 66333(g)).

A city may impose objective setbacks, but no more than four feet from the side and rear lot lines may be required for an attached or detached ADU (Gov. Code, § 66314(d)(7)).

Front setbacks are different — a city may apply them, but a front setback cannot be used to preclude an ADU of at least 800 square feet, even if that unit would sit partly or wholly within the front setback (Gov. Code, § 66321(b)(3)). If an 800-square-foot unit cannot fit in the back yard, the city must allow it in the front setback if that is what it takes to accommodate it.

Additional setbacks can apply in the Coastal Zone under a local Coastal Program (Gov. Code, § 66329).

A city may not impose a minimum lot size requirement for an ADU (Gov. Code, § 66314(b)(1)).

Lot coverage limits, floor area ratio requirements, and open space or landscaping requirements cannot be used to preclude an ADU of at least 800 square feet of interior livable space that keeps four-foot rear and side setbacks (Gov. Code, § 66321(b)(3)). They can still be applied to larger ADUs, but not so as to unreasonably restrict ADU creation.

Parking for an ADU may not exceed one space per unit or per bedroom, whichever is fewer, and those spaces may be tandem on a driveway (Gov. Code, § 66314(d)(10)). Guest parking may not be required for an ADU under any circumstances. A studio or efficiency unit has no bedrooms and so does not add to the bedroom count.

No parking at all may be required where the ADU is (Gov. Code, § 66322(a)):

1. within one-half mile walking distance of public transit;
2. within an architecturally and historically significant historic district;
3. part of the proposed or existing primary residence or an accessory structure;
4. in an area where on-street parking permits are required but not offered to the ADU's occupant;
5. within one block of a car share vehicle; or
6. submitted together with an application for a new primary dwelling on the same lot, where one of the criteria above is also met.

Replacement parking is not required. When a garage, carport, covered parking structure, or uncovered parking space is demolished or converted in connection with building an ADU, the city may not require those spaces to be replaced (Gov. Code, § 66314(d)(11)).

Impact fees are prohibited entirely on an ADU with 750 square feet or less of interior livable space, and on a JADU with 500 square feet or less. Above 750 square feet, an impact fee on an ADU must be charged proportionally to the square footage of the primary dwelling (Gov. Code, § 66311.5(c)).

An ADU or JADU with less than 500 square feet of interior livable space does not increase assessable space.

These are stated as rules, never as amounts. What any particular city's fees come to is a number for that city, and what a project costs is a question Bayfront answers after a site walk.

ADUs and JADUs subject to state law must be considered, approved or denied, and permitted ministerially — without discretionary review and without a hearing (Gov. Code, §§ 66317(a); 66335). There is no design review board deciding whether they like it.

That is why development standards have to be objective: a uniform benchmark knowable by both the applicant and the agency before an application is submitted (Gov. Code, § 66313(i)). Numeric standards like heights and setbacks qualify, as do specified colors or materials. Subjective language — "privacy," "compatibility with neighboring properties," "design harmony," "must match the existing architectural style," "high quality materials" — requires independent judgement and may not be imposed on an ADU.

Ministerially approved ADUs and JADUs are statutorily exempt from CEQA.

Two clocks run, and they were tightened on January 1, 2026.

Completeness — 15 business days. A permitting agency must decide whether an ADU or JADU application is complete and give written notice within 15 business days of receiving it. If it is incomplete, the notice must list the incomplete items and describe how to fix them (Gov. Code, §§ 66317(a)(2); 66335(a)(2)).

Decision — 60 days. Where there is an existing single-family or multifamily dwelling on the lot, the agency must approve or deny a completed application within 60 days (Gov. Code, §§ 66317(a)(3); 66335(a)(3)). The statute now says "approve or deny," replacing the older and weaker "act on." A denial must come back in writing with a full set of comments listing what is deficient and how it can be remedied.

There is also an appeal route: if an application is found incomplete or is denied, the agency must provide an appeal process and a final written determination within 60 business days of the appeal (Gov. Code, §§ 66317(d); 66335(e)).

"Permitting agency" is broad — planning, building, utilities, and special districts all count (Gov. Code, § 66313(k)).

The statutory clock is not the whole calendar. The practical timeline depends on how fast plan-check corrections are cleared, which is the part Bayfront manages.

Converting an existing garage to living space is a common ADU path and often the fastest, because the structure and foundation already exist. Three state rules make it easier than people expect:

• No replacement parking may be required for the spaces lost (Gov. Code, § 66314(d)(11)).
• No setback is required for an ADU created inside the existing structure, or for a new structure built in the same location and to the same dimensions (Gov. Code, § 66314(d)(7)).
• Unit size limits, open space, and landscaping requirements do not apply to a conversion of existing space (Gov. Code, § 66323).

Where a detached garage is being demolished and replaced with an ADU, the city must review and issue the demolition permit at the same time as the ADU construction permit (Gov. Code, § 66314(e)).

If a garage, cottage, or in-law unit was converted or built without permits — sometimes decades ago, often by a previous owner — there is a legalization path, and it is better than most people expect. This is the question behind "can I get my unpermitted unit grandfathered," "is there an amnesty," and "the work was done without a permit, am I stuck."

A local agency is precluded from denying a permit for an unpermitted ADU constructed before January 1, 2020 on the grounds that it violates building standards or does not comply with state ADU law or the local ordinance (Gov. Code, § 66311.7(a)).

Cities are required to publicise this — including a checklist of the conditions that would deem a building substandard under Health and Safety Code section 17920.3, and notice that before applying, a homeowner may obtain a confidential third-party code inspection from a licensed contractor to understand the unit's condition and the likely scope of work first (Gov. Code, § 66311.7(d)).

That confidential-inspection step is the useful part for a homeowner in this position, and it is exactly the kind of assessment Bayfront does on a site walk. Milpitas also runs a local "Safe ADU" legalization program.

By default an ADU cannot be sold separately from the main house. A local agency may adopt an ordinance permitting the separate conveyance of the primary dwelling and ADUs as condominiums (Gov. Code, § 66342). This is the AB 1033 route, and it only exists where the city has opted in — San José is the notable local example.

If someone asks how to get their permit faster, how to speed up approval, or how to cut permitting time, this is the answer — it is the largest lever a homeowner has on the clock, and most people have never heard of it.

The 30-day clock. A local agency must approve or deny an application for a detached ADU within 30 days — half the ordinary 60 — where the application uses a plan pre-approved by that agency, a plan pre-approved by any other agency in California, or a plan identical to one in a detached-ADU application the agency already approved. The plans must be valid within the current triennial California Building Standards Code cycle. (Gov. Code, § 65852.27, added by AB 1332, Chapter 759, Statutes of 2023.)

That "any other agency in the state" clause is the part people miss: a design cleared in one city can shorten a permit in another.

Cities must run a program. Since January 1, 2025 every local agency has had to develop a pre-approval program, accept plan submissions for pre-approval from any party, and post the approved plans along with the submitting party's contact information on its own website. It may also post plans pre-approved by other local or state agencies, and may charge a fee for pre-approval. Not every city has caught up.

What it does NOT cover. Pre-approval clears the building. Site plan, setbacks, utility connections, grading, and a foundation engineered for the actual soil are all still reviewed. Faster is not the same as skipped — be clear about that when a visitor assumes otherwise.

Bayfront publishes which local jurisdictions run a program at /pre-approved-plans, with links to each. Los Altos Hills publishes plans already cleared by California HCD.

Visitors mix these up. SB 9 (Chapter 162, Statutes of 2021) is the urban lot split and duplex law — it is about subdividing a parcel or adding a second primary unit. An ADU is an accessory unit on the existing lot, under a different statute and a different process. A property may have options under both, but the rules, the outcomes, and the permit path are not the same.

Note that a separate SB 9 was enacted in 2025 (Chapter 510) which amended ADU law. Two different bills share the number in different years, which is a reliable source of confusion in anything written about this.

Five 2025 bills amended state ADU law: AB 1154 (Ch. 507), SB 9 (Ch. 510), SB 543 (Ch. 520), AB 462 (Ch. 491), and AB 130 (Ch. 22). The changes that matter most to a homeowner:

• JADU owner occupancy now turns on whether the JADU has shared sanitation facilities with the house. Separate facilities means no owner-occupancy requirement.
• JADUs cannot be short-term rentals, and if rented must be rented for more than 30 days.
• A 15-business-day completeness clock, with a written list of deficiencies if the application is incomplete, and an appeal route with a 60-business-day final determination.
• Impact fees restated around interior livable space: none below 750 square feet for an ADU or 500 for a JADU, proportional above that.
• Coastal Zone applications must be approved or denied within 60 days of a completed application, and are deemed approved if the Coastal Commission misses that window with an existing primary dwelling on the lot.
• Ordinances that are not filed with HCD within 60 days, or whose findings are not answered within 30 days, are null and void — and the city must then apply state law alone.
• Several Government Code sections were renumbered, and 66333.5 was added.