California ADU rules: can I build an ADU?

Coming January 1, 2027

AB 956, signed September 29, 2026, requires cities to approve two new detached ADUs on a lot with a single-family home, instead of one. A city then doesn't have to approve a junior ADU on a lot that already has two new detached ADUs. It also extends the ban on covenants that block ADUs to every lot zoned to allow single-family homes.

Where ADUs are allowed

• In zones that allow homes. A city may limit where ADUs go only based on water and sewer capacity, traffic flow and public safety, and can't rule them out altogether (§ 66314(a)).
• No minimum lot size may be required (§ 66314(b)(1)).
• Covenants (CC&Rs) that prohibit or unreasonably restrict an ADU or JADU on a single-family lot are void (Civil Code §§ 714.3, 4751). An HOA can apply only limited objective standards.

Size

• A city's maximum size must still allow at least 850 square feet, or 1,000 square feet for an ADU with more than one bedroom (§ 66321(b)(2)).
• Where a city has no compliant ADU ordinance, the limits are 1,200 square feet for a new detached ADU (§ 66314(d)(5)) and 50% of the house's floor area for an attached one, but at least 800 square feet (§§ 66314(d)(4), 66321(b)(3)).
• Converting existing space isn't subject to unit-size limits (§ 66323(a)(1)); a converted accessory structure can add up to 150 square feet for access (§ 66323(a)(1)(A)).
• A junior ADU is at most 500 square feet, inside the house (§ 66313(d)). An efficiency unit can be as small as 150 square feet (Health and Safety Code § 17958.1).

Height

• Detached ADUs: a city can't set a limit below 16 feet (§ 66321(b)(4)(A)), or below 18 feet (plus up to 2 feet for a roof pitch matching the house) within half a mile of a major transit stop or high-quality transit corridor (§ 66321(b)(4)(B)).
• Attached ADUs: up to 25 feet or the height limit for the house, whichever is lower (§ 66321(b)(4)(D)).
• A city must allow at least two stories when they fit under the applicable height limit and building standards (§ 66321(b)(4)(D)).

Setbacks

• Side and rear setbacks can't be more than 4 feet (§ 66314(d)(7)).
• No setback is required for an ADU in existing space, or rebuilt in the same place and size as an existing structure (§ 66314(d)(7)).
• Front setbacks can't prevent an 800-square-foot ADU; lot coverage, floor-area and open-space rules can't either, with 4-foot side and rear setbacks (§ 66321(b)(3)).

Parking

• At most one space per ADU or per bedroom, whichever is less; it can be tandem on a driveway (§ 66314(d)(10)).
• No replacement parking can be required when a garage or carport is converted or demolished for an ADU (§ 66314(d)(11)).
• No parking at all can be required within half a mile walking distance of public transit, in a historic district, for an ADU inside the house or an accessory structure, where on-street permits aren't offered to the occupant, or with a car-share vehicle within a block (§ 66322(a)).

Fees

• No impact fees, including park fees, for an ADU with 750 square feet of interior living space or less, or a JADU of 500 square feet or less; above that, only in proportion to the house's size (§ 66311.5(c)(1)–(2)).
• No school fees for an ADU or JADU under 500 square feet of interior living space; above 500, school districts may charge them (§ 66311.5(c)(3); Education Code § 17620).
• An ADU or JADU isn't a new residential use for utility connection fees or capacity charges unless it's built with a new house (§ 66311.5(b)). One in existing space can't be charged them at all, unless it's built with a new house or sold separately (§ 66311.5(d)); for other ADUs they must be proportionate to the unit's size or plumbing fixtures (§ 66311.5(e)).

Fire sprinklers

• Required in an ADU or JADU only if the house itself must have them, and building an ADU doesn't trigger sprinklers for the house (§§ 66314(d)(12), 66323(d)).

Living in it, renting it, selling it

• No owner-occupancy requirement for an ADU (§ 66315). For a JADU that shares a bathroom with the house, the owner must live in the house or the JADU (§ 66333(b)).
• Cities may require rentals to be longer than 30 days (§§ 66315, 66323(e)); JADUs can't be short-term rentals (§ 66333(g)).
• An ADU can be sold separately only where a city allows it as a condominium by ordinance (§ 66342), or under a narrow nonprofit exception (§ 66341).

Permits and timing

• A city must approve or deny a complete application within 60 days (§ 66317(a)(3)); an application is deemed complete if the city doesn't say otherwise within 15 business days (§ 66317(a)(2)(F)).
• A denial must come in writing with the list of what's missing and how to fix it (§ 66317(b)).
• The 60 days start from a complete application; corrections and resubmittals add time. See how long permits actually take in Los Angeles.
• A certificate of occupancy is required before anyone lives in it (§ 66328).
• An unpermitted ADU built before 2020 can't be refused a permit for code or ADU-law violations except on specific findings (§ 66311.7(a)).

Next steps

• Read about the four kinds of ADU.
• Check your city's own ADU rules (for Los Angeles, the Department of Building and Safety).
• Talk to a licensed builder; see choosing a licensed builder.
• Look up the ADUs permitted near your address.

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