As California’s housing crisis deepens, accessory dwelling units and junior accessory dwelling units have become a centerpiece of the state's response. Over the past several years, the state legislature has built a framework that tells property owners what they can build, tells cities what they must allow, and gives the state enforcement authority when cities fall short. 

An accessory dwelling unit (ADU) is a fully independent second home on the same lot as a primary residence; this can be a detached backyard cottage, a garage conversion, or an addition attached to the main house. It has its own kitchen, bathroom, and sleeping area. ADUs include efficiency units and manufactured homes.

A junior accessory dwelling unit (JADU) is a smaller version of an ADU. It is created from space that already exists inside the primary home. A JADU is capped at 500 square feet of interior livable space and does not need to be fully independent. It may share a bathroom with the main home, or have its own. It is typically a converted bedroom suite or interior space with its own entrance and a kitchenette

What you can build depends on the type of lot you have. 

On a single-family lot, state law requires every city in California to allow at minimum one ADU and one JADU on the same lot at the same time. SB-477 allows the ADU to be attached, detached, or converted from an existing structure, like a garage. The law also says that the JADU must come from space already within the primary home.

In a multifamily lot, there are more options. Through SB-1211, there can be up to eight detached ADUs, with the condition that the number of new ADUs cannot exceed the number of units already on the property. For example, A 5-unit building can add up to 5 ADUs; a 12-unit building is capped at 8. Also, through SB-477, interior conversions of any non-livable space, like storage rooms, boiler rooms, attics, basements, garages, into ADUs are permitted. Cities must allow at least one such conversion and up to 25% of existing units to be converted this way.

Cities may set their own ADU size limits, but those limits cannot prevent construction of an ADU of at least 800 square feet of interior livable space with four-foot side and rear yard setbacks. A city can set a maximum, but it must be at least 800 square feet, and it cannot use setback rules, lot coverage requirements, or front setback requirements as a backdoor way to prevent construction.

On height, state law sets minimums that cities must allow:

• 16 feet for a detached ADU on a standard single-family or multifamily lot.
• 18 feet for a detached ADU within half a mile of a major transit stop.
• 25 feet, or the height limit that applies to the primary dwelling, for an ADU attached to the primary home, though cities are not required to allow more than two stories.

For JADUs, the cap is 500 square feet of interior livable space.

For ADUs, AB-976 permanently prohibits cities from requiring owner-occupancy as a condition of an ADU permit. You do not need to live on the property to build an ADU, rent it out, or rent out the main house simultaneously.

For JADUs, AB-1154 narrowed the owner-occupancy requirement so that it only applies when the JADU shares a bathroom with the main home. If a JADU has its own bathroom, the owner-occupancy requirement does not apply.

One statewide restriction that applies to both is that cities may require ADUs and JADUs to be rented for terms of 30 days or longer, effectively prohibiting short-term vacation rentals if a city chooses to enforce it.

SB-477 establishes that state ADU law is a floor, not a ceiling. Cities can be more permissive, allowing larger units, fewer restrictions, and more ADUs per lot, but they cannot be more restrictive than what the state requires. Any local ordinance that falls short of state law is automatically null and void, and state standards apply directly in its place.

The limits on what cities can regulate include:

Standards must be objective. Cities cannot use vague design review, neighborhood character, or subjective architectural standards to deny an ADU permit. Any standard a city imposes must be measurable and uniformly verifiable, not subject to personal judgment by a planning official.

Setbacks and size limits cannot block construction. Any size limit, setback rule, lot coverage requirement, or front setback requirement that would prevent an 800 sq ft ADU with 4-foot side and rear setbacks from being built is unenforceable.

No replacement parking. If you demolish a parking spot while building an ADU, the city cannot require you to rebuild it, whether it is covered or uncovered. Cities also cannot require parking for ADUs within half a mile of public transit, or for ADUs that are conversions of existing structures.

No fire sprinkler requirements. Cities cannot require fire sprinklers in an ADU if they are not required in the primary residence.

No nonconforming condition triggers. Cities cannot require correction of existing code violations on a property that is unrelated to the ADU as a condition of approving a permit. (SB-477)

HCD enforces compliance. The California Department of Housing and Community Development has formal enforcement authority over ADU and JADU law and actively reviews local ordinances. Cities must submit ADU ordinances to HCD within 60 days of adoption. That same requirement extends to JADU ordinances. A noncompliant ADU ordinance that a city fails to fix is nullified, and state law governs instead. The same applies to JADU ordinances.

All ADU and JADU applications are processed ministerially without a public hearing or discretionary review. The standard review window is 60 days from receipt of a completed application, and if a city fails to act within that window, the application is deemed approved.

AB-1332 requires every city and county to maintain a publicly available catalog of pre-approved ADU plans by January 1, 2025. If a homeowner uses one of those pre-approved designs, the city must approve or deny the permit within 30 days instead of 60.

AB-2221 requires that when a city denies an application, it must provide a full written explanation of every specific deficiency and describe exactly how the applicant can fix it.

If an ADU or JADU was built before January 1, 2020, a city cannot deny a permit application for it solely because it was built without one. The only grounds for denial are genuine habitability conditions. The prior amnesty cutoff was January 1, 2018. AB-2533 extended it to 2020 and expanded coverage to include JADUs for the first time. The bill also made it so cities cannot charge impact fees on amnesty units under 750 square feet. Fees for larger units must be proportionate to the primary dwelling's square footage, not flat-rate. Also, cities must post a public checklist of the health and safety standards that apply. Homeowners can also hire a licensed contractor to conduct a confidential inspection before submitting their application, which means you can find out what needs to be fixed without triggering a code enforcement action.

In cities that have opted in to AB-1033, it is possible to sell an ADU separately. The law authorizes cities to allow the separate sale of ADUs as individual condominium units, independent from the primary home. Before AB-1033, this was not possible, as ADUs had no independent title. For a deeper look into AB-1033, check out our full overview of AB-1033.

SB 1077 addresses the California Coastal Zone, which carries an additional layer of oversight from the California Coastal Commission and has historically made ADU permitting slower and more expensive in coastal communities. The bill requires the Coastal Commission and HCD, by July 1, 2026, to develop written guidance for local governments on how to streamline ADU and JADU permitting within the coastal zone.

Interested in understanding what may be possible on your site? Contact Type Five to evaluate your property, discuss your development goals, and explore how California’s infill housing laws could apply to your project.