Adu estimate — 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 ADU estimate provides a preliminary look at what your secondary unit might cost based on the size and complexity of your plans. Variables such as foundation type, square footage, and interior material quality shift the total investment up or down. You need an estimate early in the process to help determine if your vision aligns with your available budget. 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: The Peninsula, Bay Meadows, Laurel Creek, Edgewood, Downtown San Mateo — and every surrounding area.