Accessory dwelling unit construction cost — 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
The cost of building an ADU depends on your choice of materials, the square footage, and whether you are doing a garage conversion or a new detached build. Site access and utility upgrades also play a big role in the final bill. Exact pricing confirmed free on the call.
Frequently asked in San Mateo
What do neighbors in San Mateo most often ask about ADUs?
What are accessory dwelling units (ADUs) and how do they apply to San Mateo?
What is the process for an accessory dwelling unit permit in San Mateo?
Where can I find accessory dwelling unit builders near me in San Mateo?
What are the options for an affordable ADU in San Mateo?
What ADU services are available in San Mateo?
What is an ADU unit and how can it benefit my San Mateo home?
Also serving nearby: Hayward · Daly City · Oakland · Sunnyvale · Fremont
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, Shoreview, Laurel Creek, Central San Mateo, Hillsborough (nearby influence) — and every surrounding area.
Areas we serve
Browse by state, then city.
California (4)
All of California · Rialto · San Buenaventura (Ventura) · San Mateo · Vacaville