California ADU Law: Size, Permits, and Owner Occupancy

California ADU laws require every city and county to allow accessory dwelling units on residential property, and they cap what local governments can demand on size, height, setbacks, parking, owner-occupancy, and permit timing. The statewide standards sit in Government Code sections 66310–66340 (formerly 65852.2 and 65852.22), and bills signed between 2023 and 2025 added permanent protections against owner-occupancy rules, more room on multifamily lots, and a narrow path to sell an ADU as a condominium.¹

The Three Types of ADUs

State law recognizes three categories. 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 limited to 500 square feet. JADUs must include an efficiency kitchen with cooking appliances, a food-preparation counter, and storage cabinets, and they may either have their own bathroom or share one with the main house.²

How Many You Can Build

On a lot with an existing or proposed single-family home, you can build one ADU and one JADU. The ADU can be new detached construction or a conversion of existing space. The JADU must be created within the walls of the primary dwelling.¹

Multifamily properties get more. Under SB 1211, a lot with an existing multifamily building can add up to eight detached ADUs, provided 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.³

Size, Setbacks, and Height

Under the statewide default that applies when a jurisdiction has no compliant ordinance, a detached ADU can reach 1,200 square feet. Local agencies that do adopt their own ordinance can set lower 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.¹ A city or county is free to allow larger units.

Setbacks are generous. New detached ADUs require no more than a four-foot setback from side and rear lot lines. If you convert an existing garage or accessory structure into an ADU, or rebuild in the same location at the same dimensions, no setback is required at all.¹

Height limits depend on type and 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 within a half-mile walking distance of a major transit stop or high-quality transit corridor, with an extra two feet allowed to match the roof pitch of the primary home. The 18-foot limit also covers detached ADUs on lots with a multistory multifamily building.
25 feet applies to an attached ADU, or the height limit for 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.³

Parking and Fire 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 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, a local agency may require at most one parking space per ADU.¹ If you demolish a garage or carport to make room for the ADU, you do not have to replace the spaces you removed.

Sprinklers follow a simple rule. An ADU needs residential sprinklers only if the primary dwelling already has them. Building an ADU does not trigger a retrofit on the main house.⁴

Owner Occupancy and Rentals

AB 976, signed in 2023, permanently banned local agencies from imposing an owner-occupancy requirement on a standard ADU. You do not have to live on the property to rent out your ADU, and you can rent both the main house and the ADU at the same time.⁵

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 be recorded, prohibiting separate sale of the JADU.²

Both ADUs and JADUs must be rented for terms longer than 30 days, which rules out use as a vacation rental or short-term listing on platforms like Airbnb.³

The Permit Process

ADU permits are processed ministerially. The local agency checks your application against objective, published standards and either approves or denies it, with no discretionary review and no public hearing. Once your application is complete, the agency has 60 days to decide. If it does nothing in that window, the application is deemed approved automatically.¹

A 2025 update added a completeness 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 can appeal, and the agency must issue a final written determination within 60 business days of receiving your written appeal.³

A typical submittal includes a site plan showing existing structures, proposed ADU placement, and property boundaries; floor plans with the interior layout; structural calculations covering seismic and wind loads; and Title 24 energy-compliance documentation.⁶ The application itself, from your local planning or building department, asks for details on square footage, mechanical systems, utility connections, and sewage disposal. After construction, a building official inspects the finished unit, and you receive a certificate of occupancy once it passes.

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 also 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.³

Adding an ADU does not trigger a full Proposition 13 reassessment. The county assessor estimates the value of the new construction and adds that figure to the existing assessed value of the property. Your primary home stays at its current assessed level. The added tax tracks what you spend to build, since construction cost is the starting point most assessors use.

Selling an ADU Separately

AB 1033, signed in 2023, lets a city or county 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. The local jurisdiction must opt in before any homeowner there can pursue a separate sale.⁷ Where a jurisdiction has opted in, the ADU and primary home are treated as separate condominium units, and the ADU buyer receives a deed to the unit along with shared interests in the land. Without a local AB 1033 ordinance, the default still holds: the ADU cannot be sold apart from the primary residence.

Legalizing an Unpermitted ADU

Health and Safety Code section 17980.12 lets homeowners delay enforcement on older unpermitted units. If you own an ADU built before January 1, 2020, and you receive a notice of a building-code violation, you can request a five-year delay by showing that correcting the violation is not necessary to protect health and safety.⁸

The same option is available for ADUs built on or after January 1, 2020 in a jurisdiction whose ADU ordinance was noncompliant at the time of construction, provided the ordinance is compliant when 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, and any delay approved before that date stays valid for its full term.⁸

Separately, a local agency cannot force you to fix code violations on your primary dwelling as a condition of approving a new ADU or JADU permit, unless those violations create a health and safety risk.

Coastal Zone Properties

If your property sits in the coastal zone, state ADU law does not override the California Coastal Act. The Coastal Commission or the local government still evaluates projects for impacts on coastal hazards, sensitive habitat, wetlands, and public access. One concession: local governments are not required to hold a public hearing on a coastal development permit application for an ADU.⁹ SB 1077, signed in 2024, directs the Coastal Commission to publish written guidance by mid-2026 to simplify coastal-zone ADU permitting, developed with the Department of Housing and Community Development.¹⁰ Until that guidance is finalized and local coastal programs are updated, coastal-zone applicants should expect longer timelines and additional documentation.

1
California Legislative Information. California Government Code 65852.2
2
California Legislative Information. California Government Code 65852.22 – Junior Accessory Dwelling Units
3
California Department of Housing and Community Development. Accessory Dwelling Unit Handbook
4
California Department of Housing and Community Development. IB 25-004 Accessory Dwelling Unit (ADU)
5
LegiScan. California AB976 2023-2024 Regular Session Chaptered
6
California Energy Commission. 2025 Energy Code Accessory Dwelling Units (ADU) FAQs
7
Digital Democracy. AB 1033 Accessory Dwelling Units Local Ordinances Separate Sale or Conveyance
8
California Legislative Information. California Health and Safety Code 17980.12
9
California Coastal Commission. Summary of State ADU Law and the Coastal Act for SB 1077 Public Input
10
California Coastal Commission. SB 1077 ADU Guidance Development