ADU Builder in Walnut Creek

We serve Northern California across three regions: the San Francisco Bay Area, Greater Sacramento, and the Central Valley. Our published guides cover 14 counties and 88 cities. Our Castro Valley and Sacramento offices support local estimating, permit coordination, and project planning across these regions.

Financing may be available for eligible projects with approved credit. Available terms depend on lender approval, project scope, and current programs. Your project manager can review the options that apply before work begins. We also accept checks, ACH, and major credit cards.

Yes. Hamilton Exteriors holds CSLB License #1078806, active general liability coverage, and the required contractor bond. We also hold GAF Master Elite and James Hardie Elite Preferred credentials. We can provide current proof of coverage before work begins.

Permit requirements depend on the project scope and local jurisdiction. Hamilton Exteriors coordinates required applications, plan documents, corrections, and inspections. Permit fees and allowances appear in the proposal before construction begins.

A detached ADU in Walnut Creek typically costs $200,000 to $370,000 for a 600 to 800 square foot unit with mid-range finishes. Garage conversions run $150,000 to $200,000, and junior ADUs start around $150,000. Permit and impact fees add $5,000 to $8,000. These ranges include design, engineering, permits, and construction. Site-specific factors like soil conditions, utility distances, and finish level affect the final price. See our 2026 Bay Area ADU Cost Guide for a detailed breakdown.

Yes. All ADUs in Walnut Creek require a building permit from the city's Building Division. California state law requires cities to approve or deny ADU permit applications within 60 days. We handle the entire permit process — application, plan submission, and inspection scheduling — so you do not have to navigate it alone.

If you own a single-family home in Walnut Creek, you almost certainly can. State law (AB 68, SB 13, AB 881) overrides most local zoning restrictions that previously blocked ADUs. Your lot must meet setback requirements (typically 4 feet from side and rear property lines), and the ADU cannot exceed certain size limits. A site feasibility review during your design consultation confirms what is possible on your specific property.

A Junior ADU (JADU) is the most affordable option at $150,000 and up (Hamilton Exteriors 2024-2026 project data). JADUs are created within your existing home footprint, so there is no new foundation, roof, or exterior walls. The next most affordable is a garage conversion at $150,000 to $200,000, which reuses your existing garage structure.

Yes, but only on the added value, not your entire property. California's Proposition 13 protects your existing home's assessed value. The Contra Costa County Assessor will add the construction cost of the ADU to your property tax roll, typically resulting in $1,500 to $4,500 per year in additional property taxes depending on your project cost (Hamilton Exteriors 2024-2026 project data).