TL;DR — Key Takeaways
- California requires cities and counties to approve ADU applications ministerially, meaning against objective standards and without a discretionary hearing.
- Since January 1, 2026, the agency must tell you within 15 business days whether your application is complete. If it misses that deadline, the application is deemed complete.
- It then has 60 days from a complete application to approve or deny. If it does neither, the application is deemed approved.
- A denial must come in writing, with a full list of what is deficient and how to fix it. An agency cannot deny an ADU based on rules outside its ADU ordinance.
- SB 543 also added a written appeal process, with a final written decision due within 60 business days of the appeal.
- The ADU statutes were renumbered in 2024 and again in 2026. Much of what is published online still cites section numbers that no longer contain the rules.
A California city or county must tell you within 15 business days whether your ADU application is complete, and must approve or deny a complete application within 60 days. If the agency misses the first deadline, the application is deemed complete; if it misses the second, the application is deemed approved. Those rules, strengthened by SB 543 effective January 1, 2026, apply to junior ADUs as well, and they sit on top of a requirement that ADU applications be approved ministerially, without discretionary review or a hearing.
Ministerial approval
The foundation of California’s ADU framework is that approval is ministerial. An agency applies objective standards, such as height, setbacks, size, and parking, and approves an application that meets them. It does not exercise discretion, hold a public hearing, or weigh whether it likes the project.
That matters for timing because a ministerial decision has nothing to deliberate about. It also matters for denials, because an agency cannot deny an ADU on subjective grounds such as whether the design is compatible with the neighborhood’s character. The state’s housing department has repeatedly told cities that standards like “clearly subordinate” or “architecturally compatible” are not the objective standards the law permits.
The same framework applies to junior accessory dwelling units, the smaller units created within the existing space of a single-family home.
The deadlines, step by step
Completeness review: 15 business days. SB 543 requires the permitting agency to determine whether an ADU application is complete and give the applicant written notice of that determination within 15 business days of receiving it. If the agency determines the application is incomplete, the notice must identify what is missing. If the agency does not make a determination within 15 business days, the application is deemed complete.
Decision: 60 days. Once the application is complete, the agency must approve or deny it within 60 days. If it does neither, the application is deemed approved.
Denial requirements. If the agency denies the application, it must provide a full set of written comments listing the items that are defective or deficient and describing how the application can be remedied. An agency cannot rely on a local ordinance, policy, or regulation other than an ADU ordinance consistent with state law as the basis for delaying or denying the application.
Appeal: 60 business days. SB 543 added a requirement that the agency provide a written appeal process for an application found incomplete or denied, and issue a final written determination within 60 business days of receiving the written appeal.
The deadlines can be tolled at the applicant’s request, and where an ADU is submitted together with a new single-family home, the agency may delay acting on the ADU until it acts on the home.
If your city has missed one of these deadlines, the deemed-complete or deemed-approved consequence is worth asserting in writing, and promptly. Call Bay Legal at (650) 668-8000 in Northern California or (213) 668-8000 in Southern California.
What else SB 543 changed
Junior ADUs. SB 543 extended the completeness review, deemed-approval, and appeal machinery to junior ADUs, and clarified that a junior ADU may contain up to 500 square feet of interior livable space.
Fees. The rule exempting smaller units from impact fees now refers to interior livable space: an ADU of 750 square feet or less, or a junior ADU of 500 square feet or less, is exempt from impact fees, as of drafting.
School fees. An ADU or junior ADU with less than 500 square feet of interior livable space is now treated as residential construction that does not increase assessable space by 500 square feet, which generally removes it from the school impact fee.
Renumbering. SB 543 renumbered several sections within the ADU chapter. The fee provisions, the housing department’s guideline authority, and the unpermitted-ADU legalization provision all moved.
Confirm current fee treatment with the permitting agency and your builder before relying on any exemption.
What a city can no longer require
The timelines are only part of the picture. State law also removes several conditions that cities historically imposed.
Owner occupancy for ADUs. State law has permanently eliminated owner-occupancy requirements for ADUs. A city cannot require that the owner live in either the main house or the ADU as a condition of approval.
Owner occupancy for junior ADUs. A 2025 change narrowed the owner-occupancy requirement for junior ADUs, applying it only where the junior ADU shares sanitation facilities with the main home, and requires that a junior ADU rented out be rented for terms longer than 30 days, as of January 1, 2026.
Minimum lot size. A local ADU ordinance may not impose minimum lot size requirements on ADUs.
Discretionary standards. As above, only objective standards apply, and the state framework sets the maximum standards a local ordinance may impose.
Local ordinances still govern a great deal, including objective design standards, setbacks within state limits, and short-term rental rules. Confirm your jurisdiction’s current ADU ordinance before designing the unit, because an application built around the city’s actual standards is the one that clears the completeness review.
The section numbers you will see online are often wrong
This causes real confusion, including in agency correspondence.
For decades California’s ADU rules lived in Government Code section 65852.2. In 2024, SB 477 moved them into a new chapter of the Government Code, sections 66310 through 66342, and the old section no longer contains them. SB 543 then renumbered several sections within the new chapter effective January 1, 2026.
A great deal of published material, including law-firm blogs, builder websites, and some older local-agency handouts, still cites section 65852.2 for current rules. The substance often remains broadly accurate, but the citation does not. If you are writing to a city to assert a deadline, cite the current section, because citing a repealed one gives the agency an easy reason to dismiss the letter.
What happens when a city will not act
Assert the deemed status. Where a deadline has passed, a written letter stating that the application is deemed complete, or deemed approved, and citing the statute, is the first step. Many delays end there.
The state’s housing department. The Department of Housing and Community Development reviews local ADU ordinances and practices, issues findings when a jurisdiction is out of compliance, and can refer violations to the Attorney General. HCD has issued findings to cities that wrongly denied ministerial ADU applications, stating that such applications are deemed approved and that permits must issue.
Court. Where an agency refuses to perform a ministerial duty, a petition for a writ of mandate asks a court to order it to act. That is a real remedy, but it takes time and cost, and it is usually the last step rather than the first.
Other streamlining laws. Legislation in 2025 extended the Permit Streamlining Act’s timelines to ministerial housing approvals, including ADUs. For ADUs, the ADU-specific deadlines are more specific and generally more protective, and they are the ones to rely on.
When the delay is not the city’s fault
Worth saying plainly, because it determines whether pressing a deadline helps.
The completeness clock rewards a complete application, and many delays trace to applications that were not. Missing plans, inconsistent drawings, unaddressed utility or fire-access questions, and applications that do not meet objective standards produce legitimate incompleteness notices and denials. A deemed-approved argument built on a clock that was properly stopped, or on an application that never met the standards, tends to fail and to sour the relationship with the permitting staff an owner will be working with for the rest of the project.
The better course is usually to submit a complete application that meets the objective standards the first time, and to press the deadlines when the agency genuinely has not met them. ADU construction disputes covers what happens once the permit issues and the project begins.
Bay Legal advises owners and builders on ADU permitting and on enforcing the state’s deadlines. Reach us at (650) 668-8000, (213) 668-8000, or through baylegal.com/contact-us.
Frequently Asked Questions
How long may a California city take to act on an ADU application?
The agency must determine whether the application is complete within 15 business days of receiving it, and must approve or deny a complete application within 60 days. Those deadlines, strengthened by SB 543 effective January 1, 2026, apply to both ADUs and junior ADUs.
What did SB 543 change about completeness review?
It requires the permitting agency to give written notice of whether an ADU application is complete within 15 business days, identifying anything missing, and provides that an application is deemed complete if the agency misses that deadline. It also added a written appeal process with a final decision due within 60 business days.
What happens when a city misses the deadline?
If the agency misses the 15-business-day completeness deadline, the application is deemed complete. If it does not approve or deny a complete application within 60 days, the application is deemed approved. An applicant should assert that status in writing, citing the current statute.
What grounds remain for denial?
Failure to meet the objective standards in an ADU ordinance consistent with state law, and health and safety or building code deficiencies. An agency cannot deny an ADU on subjective design grounds or based on rules outside its ADU ordinance, and a denial must list every deficiency and how to fix it.
What are an applicant’s remedies against delay?
Asserting the deemed-complete or deemed-approved status in writing, using the written appeal process SB 543 added, reporting noncompliance to the Department of Housing and Community Development, and, as a last resort, petitioning a court for a writ of mandate ordering the agency to perform its ministerial duty.
