California has spent the better part of a decade rewriting its ADU rules, and almost every change has been in the homeowner’s favor. The short version: your city must review an ADU application without a public hearing, must decide within 60 days, cannot require you to live on the property, cannot make you replace parking you lose to a garage conversion, and cannot charge impact fees on units under 750 square feet.
That is a significant shift from where things stood ten years ago, when a single planning commissioner or an unhappy neighbor could stall a project indefinitely. Understanding these protections matters, because they give you a clear basis for holding a city to its obligations. Here is what the law actually provides.
Ministerial Review: No Hearing, No Discretion
This is the foundation everything else rests on.
ADU applications receive ministerial review, meaning the city applies objective standards without a discretionary hearing. If your plans meet the objective requirements, approval is required. There is no design debate, no planning commission vote, and no CEQA environmental analysis for ADUs meeting objective standards.
The practical consequence is worth stating plainly: the question is not whether you will get a permit. It is how long it takes and how many corrections you work through along the way.
The 60-Day Decision Deadline
Cities must approve or deny a complete ADU application within 60 days. If the deadline passes without a decision, the application is deemed approved.
A more recent addition closed the loophole that made this weaker than it sounded. Cities must now determine whether an application is complete within 15 business days of submittal and provide an itemized list of anything missing. If they do not respond in that window, the application is treated as complete and the 60-day clock starts.
Before this change, applications could sit untouched for months on the grounds that they had not been reviewed for completeness. That is no longer permitted.
One clarification worth understanding: the clock applies to a complete application, and correction cycles are where real timelines expand. This is an argument for submitting a thorough, accurate package rather than a fast one.
Pre-Approved Plans and the 30-Day Path
Cities are required to maintain programs of pre-approved ADU plans — accepting submissions, posting approved designs publicly, and maintaining a library homeowners can draw from. Applications using a pre-approved plan must be decided within 30 days rather than 60.
Where a pre-approved design suits your property and your needs, this can compress permitting substantially. The tradeoff is limited flexibility in layout and siting. It is worth asking your city what is in its library before assuming a custom design is necessary.
Size Limits
State law sets floors that cities cannot go below.
- Detached ADUs are generally allowed up to 1,200 square feet.
- Attached ADUs may be up to 50 percent of the primary home’s living area, and a city cannot restrict an ADU of 800 square feet or smaller regardless of that percentage.
- Junior ADUs are capped at 500 square feet and must be created within the existing home.
A recent clarification changed how square footage is measured: only interior livable space counts. Thick exterior framing and covered porches no longer consume the unit’s allowance on paper, which gives designers more usable room within the same limit.
Local rules vary within these state floors, so confirm specifics with your city.
Setbacks and Parking
Detached ADUs are entitled to four-foot rear and side setbacks. A city cannot impose more restrictive setbacks on a conforming detached ADU.
On parking, the rule that surprises homeowners most: when you convert a garage into an ADU, the city cannot require you to build replacement parking elsewhere on the lot. This single provision is what makes many garage conversions feasible on lots where replacement parking would be impossible to site.
Fees
Impact fees cannot be charged on ADUs under 750 square feet. Recent legislation additionally exempts units under 500 square feet from school impact fees.
These thresholds are worth knowing during design. A unit drawn at 780 square feet and one drawn at 740 can carry meaningfully different fee obligations, and that is a decision better made deliberately than discovered at permit issuance. Standard permit fees still apply and vary by city.
Owner Occupancy Is No Longer Required
Cities cannot impose owner-occupancy requirements on ADUs permitted after January 1, 2025. This removed a significant obstacle for homeowners who wanted the option to rent both units, or who did not want a deed restriction limiting their future flexibility.
Selling an ADU Separately
A newer law allows homeowners to sell an ADU separately from the primary residence as a condominium, in cities that have opted to participate.
This is genuinely new territory and adoption varies. If separate sale is part of your long-term thinking, confirm your city’s participation before you build, because it affects how the project should be structured from the start.
HOAs Cannot Unreasonably Restrict ADUs
Homeowners associations are prohibited from unreasonably restricting ADU construction. HOAs may still enforce reasonable aesthetic standards, but a blanket prohibition is not enforceable.
Where Local Rules Still Apply
State law sets a floor, not a ceiling, and several areas remain locally governed:
- Height limits, though state law protects certain minimums, including greater height near transit
- Objective design standards for materials and finishes
- Properties in the Coastal Zone, which carry an additional permit — though a completed coastal permit application for an ADU now also carries a 60-day decision requirement
- Properties listed on the California Register of Historical Resources, where objective protective standards may apply
- Short-term rental rules, which cities may restrict
Frequently Asked Questions
Can I build both an ADU and a JADU on the same lot?
On most single-family lots, yes. State law establishes that homeowners can build both. Specific combinations depend on lot conditions and the current statute, so confirm your situation.
What if my city denies my application?
A denial must include a specific, itemized list of what needs correcting — a city cannot deny an ADU without explaining precisely why. Recent legislation also strengthened appeal rights for denied applications.
Do I still need a building permit?
Yes, always. There is no legal path to an unpermitted ADU. Unpermitted units create serious problems at resale, expose you to liability, and can result in required removal.
Can I rent my ADU on a short-term basis?
Long-term rentals of 30 days or more are broadly protected. Short-term rentals are subject to local rules and are restricted in many Bay Area cities.
How current is this information?
California legislators revisit ADU law nearly every session, and provisions change. Treat this as an orientation rather than a final authority, and confirm current requirements with your city or your design-build team before making decisions.
Planning an ADU in the Bay Area
Design by M&M is a Bay Area design-build company working with homeowners in Palo Alto, San Francisco, and surrounding Peninsula and South Bay communities. We handle feasibility, design, permitting, and construction as one process, which means state protections and local requirements are both accounted for while the design is still taking shape.
If you are considering an ADU and want to understand what applies to your property, a consultation is the place to start. Contact Design by M&M to discuss what is possible for your lot.
