Nearly 4,000 property owners across unincorporated Sonoma County will soon be able to build a backyard cottage, converted garage or other small secondary home on their land. The Sonoma County Board of Supervisors voted on Oct. 6 to lift a zoning restriction that had barred accessory dwelling units, or ADUs, in certain areas, and the change takes effect Nov. 5.
The policy shift applies to 3,997 parcels outside the county's coastal zone, according to The Press Democrat. Those parcels carry a specific zoning designation flagging concerns around water supply, wastewater disposal, fire hazard and traffic hazard — the very issues the county says new permitting will still have to address before anyone can break ground.
Property owners hoping to add a secondary unit will not get a free pass. The station's report notes they must still go through a permitting process that considers water supply, wastewater disposal, building standards, fire safety and other zoning requirements before a project is approved.
Where the New ADU-Eligible Parcels Are
The bulk of the newly eligible land sits in two supervisorial districts. The 5th District, which covers much of western Sonoma County including the coast, has the most affected parcels at 1,487. The 4th District, located in north county, follows closely with 1,033 parcels. The 3rd District, which spans central Santa Rosa, has just 21 parcels affected — together, the 4th and 5th Districts contain the majority of the parcels covered by the change, per the same account.
An ADU, as defined by Permit Sonoma, is a small dwelling unit that may be established alongside a single-family or multifamily home in zones where that primary dwelling is already allowed. County guidance also makes clear these units are meant for long-term occupancy of 30 days or longer — they cannot be used as short-term rentals.
Why the County Had to Act
The change traces back to state scrutiny of Sonoma County's housing rules. The California Department of Housing and Community Development notified the county in 2025 that its ADU restriction in the affected areas did not comply with state law, which requires local jurisdictions to allow a certain number of ADUs in zones where other residential development is permitted. California has amended its state ADU law through a number of changes since 2023, part of a broader statewide push to expand this kind of housing.
Sonoma County had already been adjusting its local rules to keep pace. Changes to the county's inland code for ADUs and junior ADUs took effect Jan. 8, 2026, after the Board of Supervisors approved zoning-code amendments through Ordinance No. 6544 on Dec. 9, 2025, according to Permit Sonoma.
County Officials Weigh In
Rebecca Hermosillo said the change gives more property owners an opportunity to explore adding a home while preserving safeguards for water, wastewater and fire safety. She added that the policy expands housing opportunities while recognizing that every property is different. Scott Orr, Sonoma County's planning and permitting director, confirmed the policy change will apply to the 3,997 parcels outside the coastal zone.
Not every property in Sonoma County is covered by the Nov. 5 change. Permit Sonoma staff note that the county's Coastal Zone requires separate handling for any changes to ADU regulations. Coastal Zone ADUs are governed by different standards and generally require additional land-use and coastal-development permits, with requirements varying by parcel zoning and factors like lot size, square footage and setbacks, all of which must remain consistent with the adopted Local Coastal Plan.
