Accessory dwelling unit homes — 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

These are standalone residential units that function as complete homes, featuring their own kitchen, bathroom, and living area separate from the main house. You need this type of project if you want to provide a permanent, comfortable living space for family or tenants. Whether you are building a new detached structure or converting an existing space, these homes provide privacy and independence while keeping loved ones or renters close by on your existing property.

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: Laurel Creek, Bay Meadows, Downtown San Mateo, Shoreview, Edgewood — and every surrounding area.