Do You Need a Permit for an ADU in California? What State Law Says
Yes. Every ADU in California needs a building permit. State law says the city must decide on it without a hearing, within 60 days of a full application. Angel Suarez Construction draws the plans and handles the city approval for Peninsula homeowners, from San Bruno to San Francisco, Millbrae, and San Mateo.
What makes an ADU permit different from a normal remodel permit?
An ADU permit follows stricter state rules than a normal remodel permit. California Government Code Section 66317 says the city must check your plans against its written rules. The city cannot hold a hearing on your ADU. It cannot put your plan to a vote.
A normal remodel permit, like a kitchen or bath update, goes through the same building department. But it does not carry this same state rule against delay. An ADU also adds new plumbing, new power, and a full second kitchen. That means more trades and more inspections than most remodels.
Get a free written estimate and we will tell you exactly which permits your project needs before any work begins.
How long does ADU permit review take in California?
State law sets a hard 60-day clock. Under Government Code Section 66317, the city must approve or deny your finished application within 60 days. If the city misses that window, your application is deemed approved.
This rule protects you from an ADU sitting in limbo for months. It does not mean your unit is built in 60 days. It means the city's yes-or-no decision must come by then. Once permits are issued, a full ADU takes about three to six months to build. The exact time depends on the size and how much foundation work it needs.
What setback, height, and size rules does the state require?
The city checks your plans against a set list of numbers. It is not a judgment call. California Government Code Section 66321 sets that list. A city must allow a side and rear yard setback of four feet or less. This rule covers both attached and detached ADUs.
Height rules use a few clear numbers too. A standard detached ADU can rise 16 feet. Near transit, that goes up to 18 feet. A unit on a lot with an apartment building can also go up to 18 feet. Add 2 more feet near transit for a pitched roof. An attached ADU can go up to 25 feet, or your main house's height limit. You use whichever number is lower. It also caps out at two stories.
Size rules work the same way. The state says cities must allow at least 800 square feet of living space. A one-bedroom ADU can go up to 850 square feet. A unit with more than one bedroom can go up to 1,000 square feet. Knowing these numbers before you draw plans means fewer surprises later.
Does every Peninsula city handle ADU permits the same way?
Every city we serve follows the same state rules as a floor. But the local steps on top of that floor are not the same.
San Francisco has allowed ADUs citywide since 2016, in every part of the city zoned for homes. The city caps a studio or one-bedroom ADU at 850 square feet, and a two-bedroom or larger unit at 1,000 square feet. San Francisco's citywide ADU rules set the size limit, even on a large lot.
Millbrae runs its own ADU rules on top of the state's, and offers a pre-approved ADU plan through its Building Division. Building to that plan can cut down the design and review time compared with a fully custom set of plans.
San Mateo issues its own ADU building permits through its Building Department. It reviews plans under the state's ADU rules, the same rules that guide every California city. Homeowners there work with the city's building counter directly. State law sets the floor on what the city can ask for or deny.
That mix, one state floor and different local paperwork, is why it helps to work with a contractor who already knows each city's counter. We pull the permit in the city where you live, not a generic statewide form. We know which department to call when a question comes up.
What happens after your ADU permit is approved?
Once your ADU permit clears, the build starts. A full ADU takes about three to six months to build once permits are issued. The time depends on the unit's size and how much foundation work it needs.
Angel Suarez Construction draws the plans and handles the city approval as part of our home additions and ADU services. We answer the city's questions along the way, so you are not stuck with the paperwork. We build attached ADUs, which share one or more walls and some utilities with your house. We also build detached ADUs, which stand fully on their own with a full kitchen, bath, and entrance.
As of 2026, a full ADU on the Peninsula runs about $150,000 to $400,000. That is a published market range, not our quote. See what an ADU costs in the Bay Area for the full cost breakdown. Every project starts with a free visit to your home and a written estimate, before we draw a single plan.
We are a licensed California B General Building contractor, CSLB License #1085926. We have built additions and ADUs across the Peninsula since 2021. The same crew stays on your project from the foundation to the final coat, so you always know who to call. See our full remodeling and construction team for the rest of our work.
Ready to start your ADU's permit and build? Contact Angel Suarez Construction for a free written estimate. We serve San Bruno and the nearby Peninsula, including South San Francisco, San Mateo, Burlingame, Millbrae, and San Francisco.
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FAQ
Related questions
What happens if my city misses the 60-day ADU permit deadline?
California Government Code Section 66317 says if the city has not approved or denied your finished application within 60 days, it is deemed approved. The city cannot just let the clock run out to avoid a decision. That is one more reason to track your application date closely.
Can a city deny my ADU permit application in California?
A city can deny an application that breaks its written ADU rules, like a setback or size limit. What it cannot do is hold a hearing or put your ADU to a vote. It also cannot turn down a plan that meets the rules just because a neighbor objects. State law says the city must check your plans against the written rules, not put them to a vote.
Do all California cities follow the same ADU permit process?
Every city follows the same state rules as a floor, but the local steps on top differ. San Francisco has allowed ADUs citywide since 2016, with its own size caps. Millbrae offers a pre-approved ADU plan you can build to. San Mateo reviews plans through its own Building Department under the state's ADU rules. We walk each client through their own city's steps.