How long ADU permits really take

The permit is often the longest part of an ADU project, and the part owners have the least control over. Knowing the rules helps you push back when things stall.

What California law requires

California sets firm deadlines for ADU applications. According to the state ADU handbook:

• A city has 15 business days to tell you whether your application is complete. If it misses that, the application is deemed complete.
• Once complete, the city must approve or deny an ADU or JADU application within 60 days when there is an existing home on the lot.
• If the city does not act within 60 days, the application is deemed approved.
• If the city denies it, it must give you a full written list of what is wrong and how to fix it within the same 60 days.
• For a detached ADU using a plan the city has preapproved, or a plan identical to one already approved, the decision is due within 30 days.
• The city must review a demolition permit for a detached garage being replaced by an ADU at the same time as the ADU.

Those deadlines cover the city's review. They do not include the time you spend on corrections and resubmittals.

What real projects took

The San Diego pilot is a useful reality check. The agency hired a permit expediter and still found the site-built units took 12 months in permitting, against an expectation of six to eight. The manufactured unit's site plan was approved within six months. Design and predevelopment, expected to take one to two months, took four on every unit.

The statewide owner survey found that 50 percent of homeowners found it difficult to obtain an ADU permit. One owner described the review process alone taking more than 12 months. Those owners mostly built before the newest state deadlines took effect, so things may be better now. But plan for the slow version.

Outside California

Each city sets its own process. As one example, Austin lays out seven steps on its ADU page: confirm the lot qualifies, get a new address for the unit, apply, pay plan review fees, pay permit fees and activate the permit, build with inspections, then get a certificate of occupancy. Austin also warns that an active permit expires on the 181st day if no inspection has been scheduled or performed.

Where time is usually lost

• Incomplete submittals. Missing surveys, energy reports or utility plans restart the clock.
• Slow responses to corrections. The San Diego report notes that an expediter is only as fast as the architect's responses to the city.
• Utility approvals. Power and gas companies run their own review. The San Diego team started with the utility at the very beginning to avoid delays.
• Design changes. Any change after submittal can mean a new review.

How to keep your permit moving

• Ask your city whether it has preapproved ADU plans. Many California cities were required to set up a preapproval program by January 1, 2025.
• Get a survey early. The setbacks drive the design.
• Have an electrician check your panel capacity before you design. A panel upgrade or new service can add months.
• Track the dates. Write down when you submitted and when the city deemed it complete. In California, the 60 day clock is the law.
• Answer every correction in one complete response, not piecemeal.
• Consider a permit expediter in a city with a slow track record.

A realistic timeline to plan around

Based on the San Diego pilot, a realistic plan for a site-built detached ADU in a busy city looks like this:

• Design and predevelopment: about 4 months
• Permitting: 6 to 12 months
• Construction: 8 to 10 months

For a factory-built unit in the same pilot, permitting took about 6 months and construction and installation about 6. Your city may be faster. Our timeline builder lets you plug in your own numbers.

Before you call a builder: answer six questions to pick a type, rough out a budget, and save builders to My Stack as you go.