ADU Builder in Sonoma County
Custom ADUs. Designed, Permitted, Built.
Northern Hills Construction designs and builds accessory dwelling units (ADUs) across Sonoma County - detached backyard cottages, garage conversions, attached in-law units, and junior ADUs. As a licensed general contractor based in Guerneville, our father-son team manages the entire ADU process for you: site feasibility, design, permitting, and construction. One crew and one point of contact, from the first sketch to the final inspection.
Our proven 3-step method for planning, permitting, and building your ADU.
1. Feasibility & Design
Every ADU starts with your lot: zoning, setbacks, access, and utilities. California law requires ADUs to be approved ministerially, and Permit Sonoma and the county's cities set the standards for each property - we tell you exactly what your lot allows and design to fit.
2. Permits, Handled
We prepare the plans, submit them, and manage the review with your local building department. ADU approvals are ministerial in California - no discretionary hearings - but the details matter, and we handle them.
3. Build With Confidence
Our own crew builds your ADU with the same craftsmanship as our custom homes. We schedule every inspection and hand over a finished, code-compliant unit ready for move-in.
From detached backyard cottages to garage conversions and junior ADUs, we design, permit, and build every kind of accessory dwelling unit. Here is how we can add living space to your property.
Detached Backyard Cottages
A standalone ADU is the most flexible way to add a rental unit, guest house, or space for family. We handle the entire build - foundation, framing, utilities, and finishes - with a layout designed around your lot, access, and privacy.
Garage Conversions
Converting an existing garage can be one of the simplest ways to add a legal ADU. We manage the structural work, insulation, windows, and utility connections so the new space lives like a natural part of your home.
Junior ADUs & In-Law Units
A junior ADU or attached in-law unit carves efficient living space out of your existing home - a good fit for aging parents, adult children, or long-term guests. We help you compare layouts and choose what fits your property.