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Reviewed by Alexander Hamilton Li, Architect & General Contractor · CSLB #1078806 · Updated July 2026
Accessory dwelling units are the Bay Area’s fastest-growing housing type, with over 4,000 ADU permits issued across the five-county region in 2024 according to the California Department of Housing and Community Development. We build detached backyard ADUs from 400 to 1,200 square feet, convert existing garages into fully finished living spaces, and construct junior ADUs within the footprint of your existing home.
Every ADU project includes design, engineering, permit management, and construction under our 60-day permit guarantee. California’s AB 68 and SB 9 legislation eliminated most local barriers to ADU construction, including minimum lot size requirements, owner-occupancy mandates, and parking replacement rules for garage conversions.
Bay Area homeowners building ADUs typically add $150,000–$300,000 in property value while generating $2,000–$3,500 per month in rental income — making ADU construction one of the highest-ROI improvements available in the current housing market.
Our ADU and guest house process moves through four stages: feasibility and design (3–6 weeks including site assessment, architectural plans, and 3D renderings), engineering and permitting (6–10 weeks with our 60-day guarantee covering structural engineering, Title 24, and soils report), site preparation (1–2 weeks of grading, utility trenching, and foundation prep), and construction (8–16 weeks depending on whether you’re building detached, converting a garage, or constructing a junior ADU). We provide a single fixed-price contract covering all four stages so there are no gaps between design and build.
ADU construction in the Bay Area requires navigating regulations that differ not just by city but sometimes by neighborhood. In Oakland, properties in the S-7 Preservation Combining Zone face additional design review for ADUs. In Fremont, the Warm Springs and Irvington districts have specific ADU guidelines reflecting their distinct neighborhood character. San Francisco’s ADU program has streamlined permitting for buildings with 1–4 units, but properties in RH-1 (single-family) zones still face density calculations that affect the maximum ADU size. Contra Costa County’s unincorporated areas require private well and septic assessments for properties not connected to municipal services. Seismically, we engineer every ADU to Seismic Design Category D standards with site-specific foundation designs based on geotechnical data. Financing is flexible: HELOCs, construction loans, the CalHFA ADU Grant Program (up to $40,000), and some Bay Area credit unions offer ADU-specific loan products with competitive rates.
What Homeowners Say About Our Work
Real reviews from verified Northern California homeowners.
deborah maxey
in the last week
Great job and very professional the 1st photo is before and the other 2 is upon completion of work.
Eric W.
via Yelp
Hamilton Exteriors did an amazing job on my roof. The team was professional, and the quality of work was top-notch. Highly recommend!
Robert H.
via Angi
From the very first consultation, we knew we'd made the right choice. The team was knowledgeable and genuinely listened to our concerns about energy efficiency and design. We've already noticed a drop in our energy bills.
Laura G.
via Nextdoor
Hamilton Exteriors repaired extensive dry rot damage on our home's exterior. Their attention to detail and commitment to quality were evident throughout the project. Our home looks better than ever.
Frequently Asked Questions
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What areas do you serve?
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.
How does billing and financing work?
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.
Are you licensed and insured?
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.
Do I need a permit for my exterior project?
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.
What types of ADUs can I build?
Three types: Detached ADU (standalone backyard structure, up to 1,200 sq ft), Garage Conversion (convert existing garage, most cost-effective), and Junior ADU (within the main home's footprint, up to 500 sq ft). You can build both a JADU and a detached ADU on the same property.
How much rental income can an ADU generate?
Bay Area ADU rental income ranges from $2,000/month for a studio to $3,500+/month for a two-bedroom, depending on location, size, and finishes. This makes ADU construction one of the highest-ROI home improvements in the current market.
What is the step-by-step ADU construction process?
Phase 1: Site assessment and design (3–6 weeks). Phase 2: Engineering, energy calculations, and permit application (6–10 weeks). Phase 3: Site prep including grading and utility connections (1–2 weeks). Phase 4: Construction from foundation through final inspection (8–16 weeks). Total timeline: 5–9 months depending on ADU type. Garage conversions are fastest; detached ADUs on hillside lots take longest.
Can I build an ADU if my property is in a homeowners association (HOA)?
California law (AB 68 and AB 670) prohibits HOAs from outright banning ADUs on single-family lots. HOAs can impose reasonable design standards (color, materials, setbacks) but cannot effectively prohibit ADU construction. If your HOA pushes back, we can help you understand your rights under current California statute and work within any legitimate design guidelines.
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21634 Redwood Rd Unit F, Castro Valley, CA 94546
Serving Oakland, Berkeley, Fremont, San Jose, Palo Alto, Walnut Creek, San Rafael, Napa, Redwood City & more across Alameda, Contra Costa, Marin, Napa, San Mateo & Santa Clara counties. All 47 cities →