Adu 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

Obtaining an ADU permit is the legal process of getting approval from your local planning department to build or convert a secondary living space. You need this to ensure your project complies with safety codes, setbacks, and neighborhood density regulations. Skipping this step can lead to significant legal issues or problems when you try to sell your home later. Permit fees are influenced by your city’s requirements and project size. Exact pricing confirmed free on the call.

Frequently asked in San Mateo

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

All cities in California →

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: Baywood, Beresford Park, Edgewater, Featherstone, North Shoreview — and every surrounding area.