Sonoma County ADU Regulations
A clear, homeowner-friendly guide to what you can build, where you can build it, and how the permitting process works.
Understanding the Rules
ADU regulations have changed dramatically — and mostly in your favor.
If you looked into building an ADU a few years ago and were told it wasn't possible on your property, it's worth looking again. California has passed a series of laws that have significantly loosened Sonoma County ADU regulations, making it easier, faster, and more affordable to build an accessory dwelling unit than at any point in the past.
That said, the regulations can still feel confusing. There are state laws, county ordinances, and city-specific rules that all interact with each other. The information below is a general guide to help you understand the landscape. For a definitive answer about what's possible on your specific property, we recommend scheduling a free consultation with us — we'll do a feasibility assessment and give you a clear picture.
Important Note
This guide covers general Sonoma County ADU regulations as of 2025. Individual cities (Santa Rosa, Petaluma, Healdsburg, etc.) may have additional requirements. Regulations change periodically. We stay current on all local rules and can advise you on the specifics for your property.
Lot Size & Unit Size
California state law (AB 68, SB 13, AB 881) removed many of the lot size restrictions that previously limited ADU construction. Most single-family residential lots in Sonoma County are now eligible.
Setbacks & Height Limits
Setback requirements were significantly reduced by state law. The old 5-foot and 10-foot setbacks that many homeowners remember are no longer in effect for ADUs in most cases.
Parking Requirements
This is one of the most significant changes in recent years. The elimination of parking requirements has made ADU construction feasible on many properties where it wasn't before.
The Permitting Process
The permitting process can feel intimidating, but it's manageable with the right guidance. We handle the entire process for our clients — from preparing the application and plans to coordinating with the planning department and scheduling inspections.
The Process
Getting your ADU permit in Sonoma County — step by step.
The ADU permit process in Sonoma County involves several stages. Here's what to expect when you work with us:
Feasibility Assessment
We visit your property, review the zoning and lot characteristics, and determine what type and size of ADU is possible. This is free and comes with no obligation.
Design & Planning
Working with you (and your architect, if you have one), we develop plans that meet your needs, your budget, and all applicable regulations. We handle the engineering and plan preparation.
Permit Application
We submit the complete application package to the county or city planning department. By state law, they have 60 days to review and respond. We manage all communication with the planning department.
Plan Review & Approval
The planning department reviews the plans for compliance with zoning, building codes, and any local requirements. We address any corrections or requests for additional information.
Construction
Once the permit is issued, construction begins. A typical ADU takes 6 to 9 months to build. We coordinate all inspections and keep you informed throughout.
Final Inspection & Move-In
After construction is complete, the building department conducts a final inspection. Once approved, your ADU is ready for occupancy — whether that's a tenant, a family member, or your new home office.
Not sure if your property qualifies?
We offer a free feasibility assessment. We'll visit your property, review the regulations that apply, and give you a clear answer about what's possible — no obligation, no pressure.