ADU Cost & Rules in San Jose, CA
Planning an accessory dwelling unit in San Jose? Here are the current construction cost ranges, permit fees, and the zoning rules that apply to most residential lots — compiled from city and state requirements and 2026 regional cost data.
- Maximum ADU size
- 1200 sq ft
- Minimum lot size
- No minimum lot size (state law); max size 1,000–1,200 sq ft depending on lot
- Setbacks
- 4 ft side and rear
- Owner-occupancy required
- Not required
- Typical permit & city fees
- $8,000 – $30,000
- Typical timeline (design → done)
- 8–14 months
How much does an ADU cost in San Jose?
A detached new-build ADU in San Jose typically costs $250,000 – $450,000, while a garage conversion runs $120,000 – $150,000. Permit and city fees add $8,000 – $30,000, and most projects take 8–14 months from design to completion.
Do you need a permit to build an ADU in San Jose?
Yes. Every ADU in San Jose requires building permits, with typical city and permit fees of $8,000 – $30,000. Setback requirements are 4 ft side and rear, and owner occupancy is not required.
How big can an ADU be in San Jose?
ADUs in San Jose can be up to 1200 sq ft. No minimum lot size (state law); max size 1,000–1,200 sq ft depending on lot. Local note: San José's Preapproved ADU program offers same-day permit issuance for qualifying plans — the fastest, lowest-cost path in the city. The 750 sq ft threshold is the biggest fee lever: staying under it avoids school, parkland, and other impact fees.
Cost breakdown for San Jose (2026)
- Detached new-build ADU
- $250,000 – $450,000
- Garage conversion
- $120,000 – $150,000
Local note: San José's Preapproved ADU program offers same-day permit issuance for qualifying plans — the fastest, lowest-cost path in the city. The 750 sq ft threshold is the biggest fee lever: staying under it avoids school, parkland, and other impact fees.
Get an estimate for your project
Ranges above assume typical lots and standard finishes. For a number tailored to your size, type, and finish level, run the calculator:
Open the ADU Cost Calculator →Figures reflect published city fee schedules and 2026 regional construction data; rules change — confirm with the San Jose planning department before designing. Last reviewed 2026.