Accessory dwelling unit construction — 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

This involves the physical building process of your secondary unit, from site preparation and foundation pouring to framing and final finishes. You need professional construction services when you are ready to transition from blueprints to a finished, livable space. A skilled crew manages the structural integrity, plumbing, electrical, and HVAC installations, ensuring the entire building meets current safety standards and local building codes so you have a durable, high-quality home that is ready for move-in.

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: Downtown San Mateo, Bay Meadows, Hillsborough, Edgewater, Shoreview — and every surrounding area.