How much does an ADU cost in San Jose?
A practical way to plan a detached ADU, garage conversion, or JADU in San Jose: define the scope, understand City fee rules, and get a written estimate for your lot.
An accessory dwelling unit is a complete home with its own kitchen, bath, and utility connections. A meaningful budget starts with the unit type, site conditions, permit path, and the selections you want, then turns those decisions into a written scope.
What sets ADU cost
Size and unit type matter, but so do site access, utility connections, foundation needs, drainage, fire access, existing-structure condition, and the work required for permits. Smaller units still carry the essential kitchen and bathroom work, so a simple square-foot shortcut cannot price a specific lot.
Detached ADU
A new, free-standing backyard ADU requires its own foundation, roof, utility runs, and site work. The lot review identifies access and utility constraints before a design choice becomes a budget commitment.
Garage conversion
A garage conversion can reuse parts of an existing structure, but the garage condition and the required structural, utility, insulation, and permit work still determine the scope. See our garage conversion guide for the planning questions.
Junior ADU (JADU)
A JADU is built within the home's existing footprint and is capped at 500 square feet by state law. Its starting condition, utility arrangement, and whether it includes a private bathroom determine the scope.
Permits, fees, and what drives cost
The City of San José says ADUs under 750 square feet are not subject to parkland and school impact fees. It also notes that a preapproved City plan can help lower plan-review cost. Building permit fees and other project-specific fees can still apply, so confirm them for your address before choosing a size. See the City’s ADU FAQs and our permit guide.
Plan the financial case with current inputs
Rental income, financing costs, taxes, insurance, maintenance, vacancy, and resale value all depend on the property and market conditions. Use current rental comparables and lender terms for a specific address, then compare net income with a written construction scope. The City says property taxes increase based on the value of the ADU.
Related reading: whether an ADU fits on your San Jose lot and how to evaluate ADU rental income.
Sources
City rules and fees can change. Confirm the requirements for your address before designing, and use a lot-specific written estimate to price construction.
- City of San José: ADU FAQs (permit fees, impact-fee rules, rental requirements, and property-tax information).
How much does an ADU cost in San Jose?
Is a garage conversion cheaper than a detached ADU?
How can I lower my ADU cost in San Jose?
Do ADUs need permits in San Jose?
Get a real ADU number for your lot.
Get a real number for this job
We come out, measure, and put a line-item price in writing. Free, and there is no obligation to use us.
- CSLB #1050108 · licensed and insured
- Serving San Jose and the South Bay
Prefer to talk? Call or text (408) 667-4946. Office hours: Monday to Friday, 7 am to 3 pm.