ADU Regulations in Alameda County, California (2026)

Regulations at a glance

Local rules & notes

Blanket Impact Fee Waiver: The City explicitly states it does not apply development impact fees to ADUs, implying a waiver even for units >750 sq ft (which State law allows cities to charge proportionally). Deep Lot Zero Setback Exception: A unique zoning exception allows ADUs to be built with no side/rear setbacks if located deep in the lot (>75ft from front) and adjoining a neighbor's rear yard. Historic Garage Demolition Review: Demolishing a garage built prior to 1942 triggers a discretionary 'Certificate of Approval' process to check for historic resources. FEMA Flood Zone Height Bonus: ADUs in flood zones may exceed the 16-foot height limit to accommodate required floor elevations.

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

Frequently asked questions about ADU regulations in Alameda County

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

  In Alameda 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; Alameda County may follow state defaults or have local limits. Verify with Alameda County planning for your specific lot.

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

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

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

  In Alameda 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 Alameda County or county planning for your zone.

• Is ADU approval ministerial in Alameda County?

  In Alameda 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; Alameda County planning can confirm the exact process.

• Are there parking requirements for ADUs in Alameda County?

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