Junior ADU Builder in Sonoma County
Junior ADUs. Designed, Permitted, Built.
Northern Hills Construction designs and builds junior accessory dwelling units (junior ADUs) across Sonoma County - compact living space of up to 500 square feet, created within the walls of your existing single-family home. As a licensed general contractor based in Guerneville, our father-son team manages the entire junior ADU process for you: layout, design, permitting, and construction. One crew and one point of contact, from the first sketch to the final inspection.
How We Create Your Junior ADU
Common Questions
What is a junior ADU? A junior ADU is a small dwelling unit of up to 500 square feet created within an existing single-family home or an enclosed space like an attached garage. It needs its own exterior entrance and an efficiency kitchen, and it may share a bathroom with the main house - which keeps the conversion simpler than a detached ADU.
Do I have to live on the property? Usually, yes - Sonoma County requires the owner of a property with a junior ADU to live in the main house or the junior unit, though a junior ADU with its own separate bathroom can be exempt. We confirm the current rules for your property before design starts.
Can I have both a junior ADU and a regular ADU? Yes - on a single-family lot, Sonoma County allows a junior ADU along with additional ADUs, so a conversion inside the house can pair with a backyard cottage. We confirm exactly what your lot qualifies for at the first consultation.
Our proven 3-step method for planning, permitting, and building your junior ADU.
1. Feasibility & Layout
Every junior ADU starts with your home as it stands: which bedroom, den, or garage space can convert, where plumbing can reach, and how the new unit connects to the main house. California law allows a junior ADU of up to 500 square feet within the existing footprint of a single-family home - we walk the property, confirm what your local standards allow, and design a layout that makes a small footprint live well.
2. Permits, Handled
We prepare the plans, submit them, and manage the review with your local building department. Junior ADU approvals are ministerial in California - no discretionary hearings - and junior ADUs are exempt from minimum parking requirements and need no replacement parking for converted space.
3. Build With Confidence
Our own crew builds the conversion with the same craftsmanship as our custom homes. We schedule every inspection and hand over a finished, code-compliant space ready to use.
From in-law suites to long-term rentals, we turn space your home already has into comfortable, code-compliant junior ADUs. Here is how we can put that space to work.
Attached Junior ADUs
Convert a spare bedroom, den, or other part of the main house into a self-contained junior suite with its own exterior entrance and an efficiency kitchen. The unit may share a bathroom with the main home, which keeps the build simpler.
In-Law & Family Suites
Give aging parents or adult children independence under your roof: a private entrance, a kitchenette, and space of their own, with the main house just a door away. We design the layout around your family and your floor plan.
Rental-Ready Junior Units
A junior ADU adds a legal long-term rental unit without new construction on your lot. We design for privacy and durability, and handle the permits end to end, so the space is ready to rent when we hand over the keys.