ADU Regulations in Alameda, California (2026)

Regulations at a glance

Local rules & notes

Inflated Floor Area Definition: The County defines floor area as measured from the 'exterior surfaces of the exterior walls', whereas the California Building Code defines it from the 'inside perimeter'. This effectively reduces the allowable interior living space for ADUs. Restrictive Rural Policy Overlay: The County applies a 1998 'Policy for Secondary Units in Rural Residential and Agricultural Areas' to ADUs over 800 sq ft or those not meeting specific configurations, which HCD states is unauthorized. JADU Zoning Exclusion: The Ordinance explicitly permits JADUs only in R-1 and PD zones, implicitly excluding them from other zones (like R-2, R-S) where single-family homes are permitted, violating state law. Site Development Review for Conversions: The County exempts garage conversions from Site Development Review only if they meet certain standards, but HCD argues JADUs and compliant ADUs should be exempt from this discretionary review entirely.

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

Frequently asked questions about ADU regulations in Alameda

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

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

• What are the setback requirements for ADUs in Alameda?

  In Alameda, 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 planning for overlay zones or design standards that could affect your site.

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

  In Alameda, 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 or county planning for your zone.

• Is ADU approval ministerial in Alameda?

  In Alameda, 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 planning can confirm the exact process.

• Are there parking requirements for ADUs in Alameda?

  In Alameda, 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 Alameda planning for your address.