ADU Rules in Sonoma County, California
We track 2 cities in Sonoma County. Each city writes its own ADU ordinance on top of California law, so size limits, fees, and design rules differ from one city to the next. Among the cities we track, Petaluma has the lowest starting permit fees ($7,000 – $14,000).
Cities
2
Max Detached Size
1,000–1,200 sq ft
Build Costs From
$165,000
Pre-approved Plans
1 of 2 cities
Sonoma County Cities Compared
| City | Max detached | Height | Permit fees | Build cost |
|---|---|---|---|---|
| Santa Rosa | 1,200 sq ft | 16 ft | $8,000 – $16,000 | $170,000 – $360,000 |
| Petaluma | 1,000 sq ft | 16 ft detached (18 ft within half a mile of major transit | $7,000 – $14,000 | $165,000 – $330,000 |
Santa Rosa ADU rules
Santa Rosa has leaned into ADUs since the 2017 fires, and its rules track state law: 16 ft for detached units, up to 25 ft if attached, and 4 ft side and rear setbacks. Instead of its own plan set, the city points homeowners to the Napa Sonoma ADU Center plan gallery and Sonoma County's ADU Ready pre-reviewed plans. The city also has a checklist for deferring ADU fees.
Petaluma ADU rules
Petaluma permits ADUs and JADUs by right on any residentially zoned lot and requires no new parking for ADUs. Homeowners can choose a statewide exempt ADU approved under state standards without local design rules, or a local ADU under the city's form-based SmartCode standards in transect zones. The Napa Sonoma ADU Center offers free guidance for Petaluma projects.
Rules that apply in every California city are summarized in our California ADU law guide. See all California cities or compare every city side by side.