ADU rules in California: what Bay Area homeowners can build in 2026
What is the difference between an ADU and a JADU?
| ADU | Junior ADU (JADU) | |
|---|---|---|
| Where | Detached, attached, or converted space (e.g. a garage) | Inside the existing single-family home |
| Size | Cities must allow at least 800 sq ft detached; attached ADUs at least 850 sq ft (1,000 sq ft with more than one bedroom) | Up to 500 sq ft |
| Owner occupancy | Not required | Owner must live in the main house or the JADU (limited exceptions) |
| How many | At least one ADU plus one JADU on a single-family lot; some lots qualify for more (for example, a converted ADU plus a new detached ADU) | |
How tall can an ADU be, and what setbacks apply?
- Detached ADU: at least 16 feet tall is allowed; up to 18 feet (plus 2 feet for a roof pitch) near major transit or on multifamily lots.
- Attached ADU: up to 25 feet or the height limit for the main house, whichever is lower.
- Setbacks: cities can require no more than 4 feet from side and rear property lines, and front setbacks can't be used to block an 800 sq ft ADU.
Do you need parking for an ADU?
Often not. Under state law, no extra parking can be required if the property is within half a mile walking distance of public transit, in a historic district, or within one block of a car-share vehicle. Where parking is required, it's capped at one space per unit or bedroom, whichever is less. If you convert a garage into an ADU, the city generally can't require you to replace the lost parking spaces.
How long does an ADU permit take, and what fees apply?
ADU permits are reviewed ministerially, which means no public hearing. Once your application is complete, the city has 60 days to approve or deny it. ADUs under 750 sq ft don't pay impact fees; for larger units, impact fees must be proportional to the size of the main house. Plan-check and building permit fees still apply, and school or utility connection fees may apply depending on the unit and the district.
Your city still sets local details — design standards, utility connections, fire requirements — so check with your local building department. San Jose, for example, runs its own ADU program with preapproved plans.
Should you convert a garage or build a new ADU?
Converting an existing garage often costs less than building from scratch because the foundation and walls are already there. A new detached ADU gives you more freedom with layout and privacy. The right choice depends on your lot, the garage's condition and how you plan to use the unit. Our garage conversion vs. new ADU guide compares the two side by side.
Can ProRock help with an ADU?
We handle ADUs and additions from design and permits to final inspection. You can see examples of our finish work in our project gallery. If you're unsure what fits on your lot, start with a free on-site estimate.
Related: When a remodel needs a permit in San Jose.
Frequently asked questions
How big can an ADU be in California?
State law guarantees that most homeowners can build a detached ADU of at least 800 sq ft with 4-foot side and rear setbacks. Attached ADUs must be allowed at 850 sq ft, or 1,000 sq ft with more than one bedroom. Local rules may allow more.
Do I have to live on the property to build an ADU?
No. California has no owner-occupancy requirement for ADUs. Junior ADUs are different: the owner must live in the main house or the JADU, with limited exceptions.
How long does the city have to approve an ADU permit?
Local agencies must approve or deny a complete ADU application within 60 days.
Are there impact fees for an ADU?
ADUs under 750 sq ft are exempt from impact fees. Larger ADUs can be charged fees proportional to the size of the main house.
Do I need parking for an ADU?
Often not. No parking can be required within half a mile walking distance of public transit, in historic districts, or within one block of a car-share vehicle. Otherwise it is limited to one space per unit or bedroom, whichever is less.
Planning a remodel in the Bay Area?
ProRock Remodeling is a licensed general contractor (CSLB #1154078) serving San Jose to South San Francisco, with $1M liability coverage and a 2-year workmanship warranty. Call (408) 991-4744 or request a free estimate.