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One place to start an ADU or JADU anywhere in Santa Clara County: who issues your permit, how size limits differ from city to city, the County's own ADU programs, and the official links you need.
Santa Clara County has no single ADU permit office. If your home is inside a city, that city's planning and building departments review and issue your ADU permit, using its own ordinance on top of California ADU law. Only parcels in unincorporated areas are permitted by the County of Santa Clara Department of Planning and Development. Not sure which applies? Look up your address in the County Property Explorer.
State law sets the floor everywhere: on a qualifying single-family lot you can build one ADU plus one JADU (up to 500 sq ft, inside the home), and HOA rules or deed restrictions that ban ADUs are void. Size, height and fee details vary by city, which is why the table below matters.
From our city guides. Always confirm current rules with the city before you design.
| City | Max detached ADU |
|---|---|
| San Jose | Up to 1,200 sq ft |
| Sunnyvale | Up to 1,200 sq ft |
| Palo Alto | 900–1,000 sq ft |
| Mountain View | 850–1,000 sq ft |
| Santa Clara | Up to 1,000 sq ft |
| Milpitas | 1,200 sq ft |
ADU rules, FAQs and ordinance updates for unincorporated Santa Clara County.
Pre-approved plans that reduce permitting time and cost in unincorporated areas.
Permit an unpermitted ADU built before January 1, 2020.
Check your parcel's jurisdiction, zoning and site constraints by address or APN.
Submit County permit applications and check permit status online.
Current County permit fees.
Rough cost and return estimate (built by Baird + Driscoll with the Chan Zuckerberg Initiative; not a government site).
Links last checked October 21, 2026. zHeight is not affiliated with the County of Santa Clara or any city. Confirm all requirements with the agency that issues your permit.
Permit-ready plans from $7,999 for a 749 sq ft detached ADU, Title 24 included. Get a free quote.