Accessory dwelling unit permit — San Mateo, CA

Last updated: September 24, 2026

What affects the price

Building an ADU involves several moving parts that shape your total budget. The biggest factor is whether you choose a prefabricated unit or a custom build on-site. Site preparation is also significant; if your land requires extensive grading, utility trenching, or foundation work, costs will climb. Your choice of finishes—like kitchen cabinetry, flooring, and siding materials—also shifts the bottom line. We help you navigate these variables to find a setup that fits your property. Exact pricing confirmed free on the call.

About this service

An accessory dwelling unit permit is the formal authorization required from your local municipality to legally construct or legalize an ADU on your property. The application process usually involves submitting detailed site plans and building blueprints for review. This ensures the structure meets all health, safety, and zoning standards for your area. Costs for the permit process vary based on local government fees and professional design services. Exact pricing confirmed free on the call.

Frequently asked in San Mateo

Also serving nearby: Hayward · Daly City · Oakland · Sunnyvale · Fremont

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More on this: HUD ADU resources — ADU policy and financing research.

Service area details

Serving all of San Mateo — population 101,327; about 8,350 residents per square mile across 12.1 sq mi. ZIP codes covered include 94401, 94402, 94403, 94404, 94497.

Neighborhoods served in San Mateo: Bay Meadows, Burlingame Hills, Edgewood, Howard Creek, San Mateo Village, Shoreview — and every surrounding area.