ADU Contractor in San Mateo

We serve Northern California across three regions: the San Francisco Bay Area (six counties from Alameda to Santa Clara), Greater Sacramento (Sacramento out to Roseville, Folsom, and Davis), and the Central Valley (Stockton to Modesto). Our crews are based in Castro Valley. We handle permits and know the building codes for each jurisdiction, which matters because requirements and fees vary significantly between cities.

We offer $0-down financing with approved credit, 12-month same-as-cash plans, and extended terms up to 15 years for larger projects. You only pay for completed, inspected work — we never ask for full payment before the job is done. Your project manager will walk you through every option during your estimate appointment. We also accept checks, ACH, and all major credit cards.

Yes. CSLB License #1078806 — verify it anytime at cslb.ca.gov. We carry $2M general liability, full workers’ comp, and are bonded per California law. We hold GAF Master Elite, Owens Corning Preferred, CertainTeed ShingleMaster, and James Hardie Elite Preferred certifications — each requires annual training and quality audits to maintain. We’re happy to provide proof of insurance before any work begins.

Most exterior projects in Northern California require a building permit. Fees vary by city — Oakland runs $200–$600, Peninsula cities often more. We handle the entire permit process: application, plan submission, and scheduling inspections. Permit fees appear as a separate line item in your estimate so you’ll see every cost upfront. For homes in WUI fire zones (Berkeley Hills, Oakland Hills, parts of Marin), we ensure full compliance with local fire-rated material requirements.

ADU costs in San Mateo typically range from $150,000 to $350,000 depending on size, finishes, and whether it's a new build or garage conversion. With median home prices at $1,600,000, an ADU can add significant value. We provide free consultations with detailed estimates.

California's ADU laws make it possible to build on most residential lots in San Mateo. San Mateo County has streamlined the permitting process. We evaluate your property's potential during our free consultation, including setbacks, utility access, and local zoning.

From design to move-in, most ADU projects in San Mateo take 8-12 months. The San Mateo County permitting process typically takes 60-90 days, and construction runs 4-6 months. Our 60-day permit guarantee keeps your timeline on track.

Yes. We handle all ADU permitting in San Mateo and throughout San Mateo County — architectural plans, structural engineering, Title 24 energy compliance, and city submissions. Our 60-day permit guarantee means we manage the entire process.

In San Mateo, you can build detached ADUs (up to 1,200 sq ft), garage conversions, attached additions, and junior ADUs (up to 500 sq ft). Many homeowners in Sugarloaf are choosing detached ADUs for rental income or multi-generational living.

ADU permits in San Mateo go through San Mateo County's building department. California law requires 60-day approval timelines. Hamilton Exteriors handles all permit applications, plan submissions, and inspections. Our CSLB #1078806 license covers the full scope.

Yes, ADUs in San Mateo can be rented at market rates. San Mateo County does not impose rental restrictions on ADUs beyond standard landlord-tenant laws. Many San Mateo homeowners earn $2,500 to $4,000 monthly, making ADUs a strong investment.

California law limits rear and side setbacks to 4 feet for ADUs in San Mateo. Front setback follows the existing zoning. Homes in Hillsdale, San Mateo Park, Baywood, Aragon have varying lot configurations. We survey your property and design within all applicable requirements.

An ADU in San Mateo can increase property value by $150,000 to $300,000 based on size, quality, and rental potential. In the competitive Peninsula market at $1,600,000 median values, an ADU is one of the strongest return-on-investment home improvements.

ADU financing options include home equity loans, HELOCs, construction loans, and California's CalHFA ADU grant program. Hamilton Exteriors partners with lenders experienced in ADU projects and can help San Mateo homeowners explore options during consultation.