California ADU rules: what state law lets you build

What state law lets you build

State law requires cities and counties to approve, without a hearing, ADUs on lots in residential or mixed-use zones. A city may write its own ADU ordinance, but it can't ban ADUs outright, and if its ordinance is out of step with state law, state standards apply instead.

On a lot with a single-family home (existing or proposed), the city must approve any combination of:

• One ADU or one junior ADU inside existing or proposed space of the house or an existing accessory structure such as a garage. A conversion of an accessory structure may add up to 150 square feet, but only for getting in and out.
• One junior ADU (up to 500 square feet, inside the house).
• One new detached ADU with 4-foot side and rear setbacks. The city can cap it at 800 square feet of livable space.

HCD reads this to mean a single-family lot can have one converted ADU, one junior ADU and one new detached ADU at the same time.

On a lot with a multifamily building, the city must allow ADUs in non-living space such as storage rooms, attics, basements or garages (at least one, and up to 25 percent of the existing units), plus detached ADUs. With an existing multifamily building you can add up to eight detached ADUs, but no more than the number of existing units. With a proposed multifamily building the limit is two.

Coming January 1, 2027: AB 956, signed September 29, 2026, raises the number of new detached ADUs a city must approve on a single-family lot from one to two. Each can still be capped at 800 square feet. A city won't have to approve a junior ADU on a lot where two detached new ADUs have been built under this rule. As a regular (non-urgency) 2026 law, it takes effect on January 1, 2027. [1][3][4][5]

Size, height and setbacks

Sizes in state ADU law are measured in interior livable space, meaning rooms for living, sleeping, eating, cooking or sanitation. This rule took effect January 1, 2026.

• Size: A city may set maximum sizes, but not below 850 square feet, or 1,000 square feet for an ADU with more than one bedroom. Lot coverage, floor area ratio, open space, front setback and minimum lot size rules can't stop an 800-square-foot ADU with 4-foot side and rear setbacks. Under the default state standards, a detached ADU can be up to 1,200 square feet and an attached ADU up to 50 percent of the existing home's floor area.
• Height: A city must allow at least 16 feet for a detached ADU. It must allow 18 feet within a half-mile walk of a major transit stop or high-quality transit corridor, plus 2 more feet to match the main home's roof pitch. On a lot with a multistory multifamily building, the minimum is 18 feet. An attached ADU can be 25 feet or the height limit for the main home, whichever is lower, and the city doesn't have to allow more than two stories.
• Setbacks: A city can require no more than 4 feet from the side and rear lot lines. No setback can be required when you convert existing space or rebuild a structure in the same place and size.
• Lot size: A city can't impose a minimum lot size for ADUs.

Cities can allow more. HCD notes that a local ordinance may set sizes above 1,200 square feet. [3][6][7]

Parking

A city can require at most one parking space per ADU or per bedroom, whichever is less, and the space can be tandem on your driveway. It can't make you replace a garage, carport or parking space you remove to build or convert into an ADU.

No parking at all can be required if the ADU is:

• within one-half mile walking distance of public transit
• in an architecturally and historically significant historic district
• part of the existing or proposed house or an accessory structure
• where on-street parking permits are required but not offered to the ADU occupant
• within one block of a car share vehicle
• applied for together with a new home on the same lot, if it meets one of the criteria above

Junior ADUs and the state-mandated ADU types described above can't be required to add parking. [1][3][7][8]

Fees, utility connections and property tax

Impact fees: No city, special district or water company can charge impact fees on an ADU with 750 square feet or less of interior livable space, or a junior ADU of 500 square feet or less. Above 750 square feet, impact fees must be proportional to the size of the main home. HCD's example: a 1,000-square-foot ADU next to a 2,000-square-foot house could pay 50 percent of the fee for a new house.

School fees: School districts may charge fees on ADUs over 500 square feet. Units under 500 square feet don't count as adding assessable space for school fees.

Utility connections: An ADU or junior ADU converted from existing space can't be required to get a new or separate utility connection or pay a connection fee, unless it is built with a new single-family home. For other ADUs, a utility may require a separate connection, with a fee proportional to the ADU's size or plumbing fixtures.

Permit fees: A city may still charge fees to cover its costs of processing ADU permits.

Property tax: A new ADU is assessed as new construction; see how an ADU affects property taxes.

Coming January 1, 2027: SB 1117, signed September 29, 2026, changes the fee rule for ADUs over 750 square feet. Where a lot has up to two ADUs, the proportional impact fee will be charged "only on the area in excess of 750 square feet of interior livable space." Lots with more than two ADUs keep the current proportional rule. As a regular (non-urgency) 2026 law, it takes effect on January 1, 2027. [2][3][5][9][10][11]

Owner occupancy, renting and selling

A city can't require you to live on the property to build or keep an ADU. The only exception is the narrow nonprofit sale program described below. A junior ADU is different: if it shares a bathroom with the house, the owner must live in the house or the junior ADU.

You can rent out an ADU. A city may require rentals of 30 days or longer, and ADUs built under the state-mandated categories, as well as junior ADUs, must be rented for terms longer than 30 days.

An ADU generally can't be sold separately from the main home. There are two exceptions. A city may adopt an ordinance letting the house and ADU be split into condominiums. Lenders must consent, and a safety inspection is required before the condominium plan is recorded. Separately, an ADU or home built by a qualified nonprofit can be sold to a qualified low- or moderate-income buyer, with affordability restrictions that last 45 years. [1][3][12][13][14][15]

How fast the city must decide

• 15 business days: The permitting agency must tell you in writing whether your application is complete. If it is incomplete, the notice must list what's missing and how to fix it. If the agency misses this deadline, the application is deemed complete.
• 60 days: If there is already a house on the lot, the agency must approve or deny a complete application within 60 days. If it doesn't, the application is deemed approved. A denial must come with a full written list of what's deficient and how to fix it.
• Appeals: The city must offer a written appeal of an incompleteness finding or a denial, and decide it within 60 business days.
• New house at the same time: If you apply for an ADU with a new home, the city may wait to decide the ADU until it decides the home. The 60 days also pause if you ask for a delay.

Cities had to set up a program to pre-approve ADU plans by January 1, 2025. HCD says a detached ADU that uses a pre-approved plan must be approved or denied within 30 days. In the coastal zone, a coastal development permit for an ADU must also be decided within 60 days of a complete application. [2][3]

Junior ADUs, garage conversions and unpermitted units

A junior ADU is up to 500 square feet of interior livable space inside a single-family home, including an attached garage. It needs its own entrance and an efficiency kitchen, and a deed restriction bars selling it separately. See our junior ADU guide.

A garage can become an ADU (see our garage conversion guide). A detached garage can be converted, or torn down and replaced. The city must review the demolition permit with the ADU application and issue both at the same time. It can't require you to replace the lost parking.

If you have an ADU or junior ADU built without permits before January 1, 2020, the city generally can't deny a permit to legalize it just because it violates building standards or ADU rules. It can deny the permit only if a fix is needed to meet the health and safety standards for substandard buildings. You won't owe impact fees or connection charges except where utility work is needed for health and safety. Cities must publish a checklist of those conditions and tell homeowners they can get a confidential inspection from a licensed contractor before applying. [3][7][13][16][17]

Lot splits, duplexes and small-lot subdivisions

SB 9 lets you build up to two homes on a lot in a single-family zone and split the lot once into two parcels. Both are approved without a hearing, and the city must decide within 60 days. After a split, the city only has to allow two units per new lot, counting ADUs. HCD says SB 9 allows up to four units in the lot area typically used for one single-family home. Details are in our SB 9 lot split guide.

Small-lot subdivisions under Government Code 66499.41 (SB 684, as amended) require ministerial review of maps creating 10 or fewer parcels with 10 or fewer homes. They apply on qualifying lots zoned for multifamily use or vacant single-family lots up to 1.5 acres. A city doesn't have to allow ADUs on lots created this way. [3][18][19][20][21]

If your city says no

Start with your city's own process. A denial must list what's wrong and how to fix it, and you have a right to a written appeal.

Since January 1, 2024, the state Department of Housing and Community Development (HCD) has had authority to enforce all of the state's ADU laws. Questions and reports of possible violations go through HCD's online ADU Portal. HCD may give technical assistance after you've applied, but it may not follow up with a city if there is no pending application. Violations can be referred to the California Attorney General.

You can see the letters HCD has sent to cities in its technical assistance and enforcement letters dashboard. Cities must send their ADU ordinances to HCD within 60 days of adopting them. If a city doesn't submit its ordinance, or doesn't respond to HCD's findings within 30 days, the ordinance is void and only state ADU law applies.

On lots zoned for single-family homes, homeowners association rules that effectively ban or unreasonably restrict ADUs and junior ADUs are void. [2][3][22]

Where local rules differ

State law sets the floor. Your city sets the details: design standards, fees, which office reviews plans, and whether it offers pre-approved plans, larger sizes or extra height. State law doesn't limit a city's ability to adopt less restrictive rules. When a city's web page seems stricter than the rules above, it may predate the 2025 and 2026 changes. Ask the city which ordinance it is applying.

City guides: Los Angeles, San Diego, San Jose, San Francisco, Sacramento, Oakland, Long Beach, Berkeley and Pasadena.

HCD's ADU Handbook, updated March 2026, is the state's main plain-language guide to these rules. [3][22]

California laws to know

• State ADU Law (Gov. Code 66310-66342)

  The core ADU and junior ADU rules, renumbered into this chapter by SB 477 in 2024. [3]

• AB 976 (2023)

  Made the ban on owner-occupancy requirements for ADUs permanent. [3][12]

• AB 1033 (2023)

  Lets a city adopt an ordinance allowing an ADU to be sold separately as a condominium. [3][14]

• SB 1211 (2024)

  Allows up to eight detached ADUs on a lot with an existing multifamily building, and ends replacement of lost uncovered parking. [1][3]

• AB 2533 (2024)

  Limits when a city can deny a permit to legalize an ADU or junior ADU built before 2020. [3][17]

• SB 543 and AB 1154 (2025)

  Took effect January 1, 2026: size measured as interior livable space, a 15-business-day completeness deadline, and new junior ADU owner-occupancy and rental rules. [3]

• AB 956 and SB 1117 (2026)

  Starting January 1, 2027: two detached new ADUs on single-family lots, and impact fees on larger ADUs charged only on space over 750 sq ft. [4][5][11]

• SB 9 (2021)

  Two homes on a single-family lot and a one-time urban lot split, approved without a hearing. [18][19]

• SB 684 small-lot subdivisions (Gov. Code 66499.41)

  Ministerial maps for up to 10 lots and 10 homes on qualifying multifamily lots and small vacant single-family lots. [20]

Questions people ask