California ADU rules in 2026, in plain English.

Last reviewed November 2026. This is general information, not legal advice; local rules change, so confirm requirements with your city or county before you design.

The basics

California ADU law is now found in Government Code sections 66310 through 66342, and the state Department of Housing and Community Development (HCD) publishes an ADU Handbook that interprets it. The current handbook is labeled "Updated March 2026" and includes an addendum on changes that took effect January 1, 2026 (HCD ADU Handbook).

The key idea: state law sets minimum standards that cities and counties must allow. A city can be more generous, and it can regulate some details, but it cannot block an ADU that meets the state standards. Under 2025 legislation, a local ADU ordinance that is not submitted to HCD, or is not fixed after HCD finds problems, becomes void, and state law applies instead.

How many units you can build

Single-family lots: state law allows a converted ADU, a junior ADU and a new detached ADU to be combined on one lot (HCD).

Multifamily lots: ADUs can be created in non-livable space such as storage rooms or garages (at least one, up to 25 percent of the existing units), plus detached ADUs: up to two on a lot with a proposed multifamily building, or up to eight on a lot with an existing one, not exceeding the number of existing units (SB 1211, 2024).

Junior ADUs: one per lot, within the walls of a single-family home. Attached garages count as within the home.

Size limits

• No local rule may prevent an ADU of at least 800 square feet of interior livable space with 4-foot side and rear setbacks (Gov. Code 66321(b)(3)).
• A city's maximum ADU size cannot be set below 850 square feet, or 1,000 square feet for an ADU with more than one bedroom (Gov. Code 66321(b)(2)).
• Junior ADUs can be up to 500 square feet of interior livable space.
• As of 2026, size limits are measured in interior livable space (SB 543).

Many local ordinances limit attached ADUs to a percentage of the main home's floor area, commonly 50 percent, but the 800-square-foot guarantee still applies.

Height and setbacks

Local height limits cannot be lower than (Gov. Code 66321(b)(4)):

Setbacks: new detached ADUs get 4-foot side and rear setbacks. ADUs converted from existing space need no additional side or rear setback beyond what is needed for fire safety.

Parking

Where parking can be required at all, it is capped at one space per ADU or per bedroom, whichever is less. And when a garage or carport is demolished or converted to create an ADU, those spaces do not have to be replaced.

No ADU parking may be required at all when the ADU is within one-half mile walking distance of public transit, in a historic district, part of the existing home or an existing accessory structure, where on-street parking permits are required but not offered to the ADU occupant, or within one block of a car-share vehicle. Junior ADUs never require parking (HCD).

Impact fees

ADUs of 750 square feet or less of interior livable space are exempt from impact fees. Larger ADUs may only be charged impact fees proportional to the square footage of the main home. JADUs of 500 square feet or less are also exempt. Plan check, permit, school and utility connection fees are separate. See our cost guide for how this affects your budget.

Owner occupancy and rentals

• ADUs: a city cannot require the owner to live on the property (the exception is when units are sold separately under a local condominium ordinance).
• JADUs: since January 1, 2026 (AB 1154), owner occupancy may only be required for a JADU that shares a bathroom with the main house.
• Short-term rentals: JADUs may not be rented for 30 days or less, and cities may also restrict short-term rental of ADUs.

Permit timelines

A city or county must approve or deny a complete ADU application within 60 days when there is an existing home on the lot. Under SB 543, effective January 1, 2026, the agency must tell you within 15 business days if the application is incomplete, or it is deemed complete. Appeals of denials or incompleteness findings must be decided within 60 business days.

In practice, the clock only starts when the application is complete, which is why clean, coordinated plans matter.

Pre-approved plans

AB 1332 required every city and county to have a program for pre-approving ADU plans by January 1, 2025. Several cities in this area now publish free or discounted plans, including the City of Ventura, Moorpark, unincorporated Ventura County, Carpinteria, Santa Barbara and Agoura Hills. Pre-approved plans still need a site plan, utilities and often Title 24 and MEP drawings for your lot. Each service area page notes what that city offers.

Coastal zone

ADU law applies in the Coastal Zone, but it does not weaken Coastal Act protections. Where a city's certified Local Coastal Program includes ADU provisions, the coastal permit must be approved or denied within 60 days, without a public hearing, alongside the ADU permit. Parts of Ventura, Oxnard, Port Hueneme, Carpinteria, Santa Barbara and all of Malibu are in the Coastal Zone.

Selling, SB 9 and unpermitted units

• Selling an ADU separately: AB 1033 lets a city or county adopt an ordinance allowing the home and ADUs to be sold separately as condominiums. It only applies where the local agency opts in.
• SB 9: a different law that requires ministerial approval of up to two primary units on a single-family parcel, or a one-time lot split into two parcels with up to two units each (HCD SB 9 fact sheet).
• Unpermitted ADUs: AB 2533 protects many unpermitted ADUs built before January 1, 2020 from being denied a permit solely because they were unpermitted, unless there is a health and safety issue.

Why local rules still matter

State law sets the floor, but your city still controls things like design standards, front setbacks, landscaping, fire-zone construction requirements, historic district review and coastal permits. HCD regularly reviews local ordinances and has sent letters to several cities in this area identifying provisions that do not comply with state law. When a local rule conflicts with state law, state law controls, but sorting out which rules actually apply to your lot is an important part of the feasibility stage.