ADU Regulations in Sonoma County, California (2026)

Regulations at a glance

Local rules & notes

Groundwater Availability Restrictions: ADUs in Class 4 groundwater areas require a professional report certifying no net increase in water use, potentially requiring rainwater catchment or offsets. Solar Access Protection: The ordinance prohibits ADUs that would substantially reduce solar access to neighboring properties. Minimum Parcel Size for ADUs: Unlike state law which generally allows ADUs on any residential lot, this ordinance requires 5,000 sq. ft. in urban areas and up to 2.0 acres for lots with wells/septic.

For the official ordinance and latest updates, check your city or county planning department.

Frequently asked questions about ADU regulations in Sonoma County

• What is the maximum ADU size in Sonoma County, California?

  In Sonoma County, the maximum ADU size is typically 1200 square feet, depending on whether the unit is attached or detached. California state law allows up to 1,200 sq ft for detached ADUs and 800 sq ft for attached in many jurisdictions; Sonoma County may follow state defaults or have local limits. Verify with Sonoma County planning for your specific lot.

• What are the setback requirements for ADUs in Sonoma County?

  In Sonoma County, typical setback requirements are 4 feet from the side property line and 5 feet from the rear. These may be reduced to 4 feet under California Government Code § 65852.2 where applicable. Check with Sonoma County planning for overlay zones or design standards that could affect your site.

• What is the maximum height for an ADU in Sonoma County?

  In Sonoma County, the maximum height for an ADU is generally 16 feet. State law often allows up to 16 feet for detached ADUs and up to 25 feet when within 4 feet of the property line in some cases. Confirm with Sonoma County or county planning for your zone.

• Is ADU approval ministerial in Sonoma County?

  In Sonoma County, ADU approval is typically Ministerial (by-right) per Gov Code §65852.2. Ministerial (by-right) review means the city must approve qualifying applications without discretionary review, per California Gov Code § 65852.2. Your project must still meet objective standards; Sonoma County planning can confirm the exact process.

• Are there parking requirements for ADUs in Sonoma County?

  In Sonoma County, parking for ADUs is generally true. California law often waives parking for ADUs within a half-mile of transit or in certain historic districts. Check with Sonoma County planning for your address.