California's Accessory Dwelling Unit laws represent the most aggressive pro-housing legislation in United States history. Beginning with Assembly Bill 2299 in 2016 and accelerating through AB 670 (2019), AB 68 (2020), SB 9 (2022), and AB 2221 (2023), California has systematically dismantled local barriers to ADU construction—transforming what was once a complicated discretionary approval into a streamlined ministerial process that cities must complete within 60 days.
The Legal Foundation: Government Code § 65852.2
Government Code § 65852.2 is the cornerstone of California ADU law. It mandates that cities and counties approve ADU permit applications "ministerially"—without discretionary review, public hearings, or design review board approval. Ministerial approval means that if your project meets the objective zoning and building standards in your jurisdiction, the city must approve it. The planning department cannot deny your application based on neighborhood aesthetics or a general preference for low-density development.
Under current state law, cities must act on a complete ADU permit application within 60 days. If no action is taken within that window, the application is deemed approved by operation of law—a provision added in 2020 that gives homeowners real legal recourse when cities stall. Any denial must be in writing with specific findings identifying which objective standard the project failed to meet.
What Cities Cannot Restrict
Current law prevents cities from: prohibiting ADUs outright on any single-family or multi-family residential lot; requiring owner-occupancy for detached ADUs (eliminated statewide effective January 1, 2020); imposing minimum lot size requirements greater than those for the primary dwelling; requiring replacement parking when a garage is converted to an ADU; applying setbacks greater than 4 feet from rear and interior side property lines for detached ADUs up to 800 square feet; limiting ADU size below 850 square feet for a studio or one-bedroom unit, or below 1,000 square feet for a two-bedroom unit; or charging impact fees on ADUs under 750 square feet.
By-Right ADUs: What's Always Allowed
State law guarantees that certain ADU types must be approved by right on any single-family residential parcel, regardless of local zoning restrictions: one detached ADU of up to 800 square feet with 16-foot height and 4-foot setbacks; one attached ADU of up to 50% of the primary dwelling's square footage; one Junior ADU (JADU) of up to 500 square feet within the existing structure; and conversion of any existing permitted accessory structure to an ADU with no setback requirements applied to the conversion footprint.
AB 670: HOAs Cannot Block Your ADU
Assembly Bill 670, signed into law in September 2019, addressed one of the most common obstacles California homeowners faced: homeowners association restrictions. Civil Code § 4751 now declares void any provision in a common interest development's governing documents—CC&Rs, bylaws, or architectural guidelines—that effectively prohibits or unreasonably restricts the construction or use of an ADU or JADU on a single-family residential lot.
Your homeowners association cannot require HOA board approval before you apply for a building permit, cannot prohibit ADUs through blanket architectural guidelines, and cannot impose restrictions that make ADU construction economically infeasible. HOAs retain the right to impose reasonable architectural standards—requiring exterior materials that match the primary dwelling—but cannot use such standards as a pretext for denial.
SB 9: Lot Splits and Urban Duplexes
Senate Bill 9, effective January 1, 2022, expanded housing options further. Under SB 9, owners of single-family residential parcels in urbanized areas may build a duplex on their property by right, or split their lot into two parcels and build two units on each—potentially creating four units on what was previously a single-family parcel. SB 9 works alongside existing ADU rights rather than replacing them.
Impact Fee Limitations
For ADUs under 750 square feet, no impact fees of any kind may be charged. For larger ADUs, fees must be proportional to the ADU's size relative to the primary dwelling. Utility connection fees are also constrained: if the ADU uses the same water and sewer connections as the primary residence, no new connection fee may be charged.
What Local Jurisdictions Still Control
Cities retain authority over objective development standards for ADUs that exceed the state by-right minimums: maximum height (cannot be set below 16 feet for detached ADUs), setbacks for ADUs larger than 800 square feet, objective architectural standards consistent with the existing neighborhood, maximum ADU size (cannot be set below 1,000 sq ft for a 2+ bedroom unit), and lot coverage standards—provided those standards do not effectively prohibit ADU construction.
Using the Law to Your Advantage
Understanding California ADU law gives homeowners real leverage when working with local planning and building departments. If a planner tells you that your city prohibits detached ADUs, requires owner-occupancy, or imposes setbacks greater than 4 feet for an 800-square-foot unit, you can cite § 65852.2 directly. The most effective strategy is to submit a complete application from day one—permit-ready drawings that demonstrate compliance with both state minimums and your city's applicable objective standards. A complete application starts the 60-day approval clock immediately.