When an ADU needs a permit
An accessory dwelling unit, whether it's a conversion of existing space, an addition, or a new detached structure, needs a full building permit in nearly every city we cover; there is no small-ADU exemption the way there is for a small shed.
What differs is what the city can demand during that permit process: state preemption laws in places like California, Washington, Oregon, and a growing list of others limit owner-occupancy requirements, parking minimums, and setback rules a city can impose on an ADU.
What an ADU permit costs
ADU permit fees are usually calculated from project valuation, the same way a home addition is, so they scale with the size and complexity of the unit; a simple interior conversion costs less to permit than a new detached structure with its own foundation and utility connections.
Plan review fees, often a percentage of the base permit fee, add to the total, and separate trade permits for electrical, plumbing, and mechanical work on a habitable second unit typically apply on top of the building permit itself.
How long review takes
ADU plan review tends to run longer than a deck or shed permit because the unit is a habitable dwelling, which means fire, life-safety, and utility connections all get checked.
Several state laws now put a cap on how long a city can take to review a compliant ADU application, often somewhere around 60 days, specifically to prevent cities from stalling ADU approvals indefinitely.
What varies from city to city
Maximum unit size, parking requirements, owner-occupancy rules, and setback minimums for ADUs vary not just city to city but increasingly state to state, since state preemption laws set a floor that local code cannot go below.
A city in a state with strong ADU preemption may be barred from requiring extra parking or an owner living on site, while a city in a state without such a law can still impose both.
What happens if you skip it
Building an ADU without a permit carries a higher cost of being caught than most accessory structures, because an unpermitted habitable unit raises fire and life-safety concerns beyond a simple zoning violation.
Retroactive permitting for an ADU often means opening up walls or ceilings to inspect wiring and plumbing that should have been checked during construction, and some cities will not let you rent the unit out until it passes that inspection.
Find your city
ADU permit guides by city
AZ
CA
- Los Angeles, CA: ADU permit guide
- Oakland, CA: ADU permit guide
- Sacramento, CA: ADU permit guide
- San Diego, CA: ADU permit guide
- San Francisco, CA: ADU permit guide
- San Jose, CA: ADU permit guide
CO
DC
FL
GA
IL
MA
MI
MN
NC
OR
PA
TN
TX
- Austin, TX: ADU permit guide
- Dallas, TX: ADU permit guide
- Houston, TX: ADU permit guide
- San Antonio, TX: ADU permit guide
WA
Compare across cities
FAQ
Common ADU permit questions
Do I need a permit to build an ADU?
Yes, in every city we track. There is no size exemption for an ADU the way there is for a small shed, since it's a habitable dwelling unit.
Can my city require me to live on the property to build an ADU?
It depends on your state. A growing number of state laws bar cities from requiring owner occupancy for an ADU, though cities in states without such a law can still impose it.
How long does ADU permit review take?
Longer than a deck or shed in most cases, since it involves full habitability review. Several states now cap review time for a compliant application, often around 60 days.
How much does an ADU permit cost?
Fees are typically based on project valuation, so a simple interior conversion costs less to permit than a new detached unit with its own foundation and utilities.
Does state law override my city's ADU rules?
In states with ADU preemption laws, yes, for specific things like parking minimums, owner occupancy, and setbacks. The city still issues the permit, but it cannot go below what the state law allows.
Disclaimer: Informational only, not legal advice. Rules change. Verify with your city's permitting staff before you build.