California ADU laws require every city and county to allow accessory dwelling units on residential property, and they set statewide minimums for size, height, setbacks, parking, and permit processing that local governments cannot undercut. Recent bills signed between 2023 and 2025 went further: they permanently banned owner-occupancy requirements for standard ADUs, expanded what you can build on multifamily lots, and opened a path to sell an ADU as a condominium in cities that opt in. The rules reward homeowners who know the specifics.
The Three Kinds of ADU
State law recognizes three categories, and which one you build changes almost every rule that follows. A detached ADU is a standalone structure separate from the main house. An attached ADU shares at least one wall with the primary residence. A junior ADU, or JADU, is carved out of the existing footprint of a single-family home and is capped at 500 square feet. A JADU must include an efficiency kitchen with cooking appliances, a food-preparation counter, and storage cabinets, and it may either have its own bathroom or share one with the main house.1California Legislative Information. California Government Code 65852.22 – Junior Accessory Dwelling Units
How Many You Can Build
On a lot with an existing or proposed single-family home, you can build one ADU plus one JADU. The ADU can be detached new construction or a conversion of existing space; the JADU must be created within the walls of the primary dwelling.2California Legislative Information. California Government Code 65852.2
Multifamily lots get more room. Under SB 1211, a lot with an existing multifamily building can add up to eight detached ADUs, as long as the number of new ADUs does not exceed the number of existing units on the lot. A lot with a proposed (not yet built) multifamily dwelling stays limited to two detached ADUs.3California Department of Housing and Community Development. Accessory Dwelling Unit Handbook
Size Limits
Where a local jurisdiction has not adopted its own compliant ADU ordinance, a detached ADU can be up to 1,200 square feet under the statewide default. Local agencies that do adopt an ordinance can set their own maximums, but the floor is 850 square feet for a studio or one-bedroom and 1,000 square feet for units with two or more bedrooms. Local governments cannot restrict the number of bedrooms. An attached ADU cannot exceed 50 percent of the existing primary dwelling’s floor area.2California Legislative Information. California Government Code 65852.2 A local agency may also adopt more generous limits above 1,200 square feet.3California Department of Housing and Community Development. Accessory Dwelling Unit Handbook
Setbacks, Height, and Placement
New detached ADUs need no more than a four-foot setback from the side and rear lot lines. If you are converting an existing garage or accessory structure into an ADU, or rebuilding one in the same location at the same dimensions, no setback is required at all.2California Legislative Information. California Government Code 65852.2
Height limits depend on the type of ADU and the property’s location:
- 16 feet is the baseline for a detached ADU on any lot with an existing or proposed single-family or multifamily dwelling.
- 18 feet applies to a detached ADU on a lot within a half-mile walking distance of a major transit stop or high-quality transit corridor, and to detached ADUs on lots with a multistory multifamily building. An extra two feet above 18 is allowed to match the roof pitch of the primary home.
- 25 feet is the ceiling for an attached ADU, or the height limit that applies to the primary dwelling under local zoning, whichever is lower.
Two-story detached ADUs are allowed whenever the height limits accommodate them, even if local zoning restricts the primary dwelling to one story.3California Department of Housing and Community Development. Accessory Dwelling Unit Handbook
Parking and Sprinklers
No parking space is required for an ADU in any of these situations:
- The ADU is within a half-mile walking distance of public transit.
- The ADU is located in an architecturally and historically significant historic district.
- The ADU is part of the primary residence or an existing accessory structure.
- On-street parking permits are required in the area but not offered to the ADU occupant.
- A car-share vehicle is located within one block of the ADU.
If none of those exemptions apply, the most a local agency can require is one space per ADU.2California Legislative Information. California Government Code 65852.2 When you demolish a garage or carport to make room for the ADU, no replacement parking is required for the spaces you removed.
Fire sprinklers follow a simple rule. An ADU needs residential sprinklers only if the primary dwelling already has them, and building the ADU does not trigger a requirement to retrofit sprinklers into the main house.4California Department of Housing and Community Development. IB 25-004 Accessory Dwelling Unit (ADU)
Who Has to Live There, and How You Can Rent It
AB 976, signed in 2023, permanently banned local agencies from imposing an owner-occupancy requirement on any standard ADU. You do not need to live on the property to rent one out, and you can rent both the main house and the ADU at the same time.5LegiScan. California AB976 2023-2024 Regular Session Chaptered That replaced the earlier temporary moratorium under SB 13.
JADUs are different. The owner must live in either the JADU or the remaining portion of the primary home. This does not apply when the owner is a government agency, land trust, or housing organization. A deed restriction running with the land must also be recorded, prohibiting the separate sale of the JADU.1California Legislative Information. California Government Code 65852.22 – Junior Accessory Dwelling Units
Both ADUs and JADUs must be rented for terms longer than 30 days, which effectively bars their use as vacation rentals or short-term rentals through platforms like Airbnb.3California Department of Housing and Community Development. Accessory Dwelling Unit Handbook
Selling an ADU Separately
Under AB 1033, signed in 2023, a local government may adopt an ordinance allowing ADUs on single-family lots to be sold separately from the primary dwelling as condominium interests. This is not a statewide right. A city or county must affirmatively opt in before any homeowner there can pursue a separate sale.6Digital Democracy. AB 1033 Accessory Dwelling Units Local Ordinances Separate Sale or Conveyance
Where a jurisdiction has opted in, the ADU and primary home are each treated as separate condominium units, so the ADU buyer receives a deed to just that unit along with shared interests in the land. If your city or county has not adopted an AB 1033 ordinance, the general rule still applies: the ADU cannot be sold apart from the primary residence.
The Permit Process and Timing
ADU permits are processed ministerially. The local agency reviews your application against objective, published standards and either approves or denies it, without discretionary review and without a public hearing. Once you submit a complete application, the agency has 60 days to approve or deny it, and if it does nothing within that window the application is deemed approved automatically.2California Legislative Information. California Government Code 65852.2
A 2025 update added an earlier checkpoint. The permitting agency must decide whether your application is complete and send you a written determination within 15 business days of receiving it. If your application is found incomplete or denied, you have a right to appeal, and the agency must issue a final written determination within 60 business days of receiving your written appeal.3California Department of Housing and Community Development. Accessory Dwelling Unit Handbook
What to Submit
A typical application package includes a site plan showing existing structures, proposed ADU placement, and property boundaries. You will also need floor plans with the interior layout, structural calculations demonstrating the building can handle seismic and wind loads, and Title 24 energy-compliance documentation showing the unit meets California’s building energy efficiency standards.7California Energy Commission. 2025 Energy Code Accessory Dwelling Units (ADU) FAQs The application itself, obtained from your local planning or building department, requires details on proposed square footage, mechanical systems, utility connections, and sewage disposal. After construction, a building official inspects the finished unit and, once it passes, issues the certificate of occupancy that legally allows someone to move in.
Fees and Property Taxes
ADUs with 750 square feet or less of livable space are exempt from local development impact fees. JADUs at 500 square feet or less are similarly exempt. For ADUs larger than 750 square feet, impact fees must be charged proportionally based on the ADU’s square footage relative to the primary dwelling, not at the full rate a new home would pay.3California Department of Housing and Community Development. Accessory Dwelling Unit Handbook The proportional calculation often saves thousands of dollars compared to standard impact fees for new construction.
Adding an ADU does not trigger a full reassessment of your property under Proposition 13. The county assessor estimates the value of the new construction and adds that figure to your existing assessed value. The primary home stays at its current (often much lower) assessed level. The additional tax depends on what you spend to build, since construction cost is the starting point most assessors use.
Legalizing an Older Unpermitted ADU
California has an enforcement-delay program that gives homeowners breathing room to bring older unpermitted units up to code. Under Health and Safety Code section 17980.12, if you own an ADU built before January 1, 2020, and you receive notice of a building-code violation, you can request a five-year delay in enforcement by showing that correcting the violation is not necessary to protect health and safety.8California Legislative Information. California Health and Safety Code 17980.12
The same option is available for ADUs built on or after January 1, 2020, in a jurisdiction that had a noncompliant ADU ordinance at the time of construction, provided the ordinance is compliant at the time the request is made. The enforcement agency must consult with the State Fire Marshal before granting the delay. New delay applications are accepted through December 31, 2029, but any delay approved before that date stays valid for its full term.8California Legislative Information. California Health and Safety Code 17980.12
Separately, a local agency cannot require you to fix code violations on your primary dwelling as a condition for approving a permit to build a new ADU or JADU, unless the violations create a health and safety risk. Cities cannot use ADU applications as leverage to force unrelated upgrades to the main house.
If Your Property Is in the Coastal Zone
State ADU law does not override the California Coastal Act. If your property sits in the coastal zone, the Coastal Commission or the local government still evaluates proposed ADUs for impacts on coastal hazards, sensitive habitat, wetlands, and public access. The one concession is that local governments are not required to hold a public hearing on a coastal development permit application for an ADU.9California Coastal Commission. Summary of State ADU Law and the Coastal Act for SB 1077 Public Input SB 1077, signed in 2024, directed the Coastal Commission to develop written guidance by mid-2026 to simplify coastal-zone ADU permitting.10California Coastal Commission. SB 1077 ADU Guidance Development Until that guidance is finalized and local coastal programs are amended, coastal-zone applicants should expect longer timelines and additional documentation than inland applicants face.