Mendocino County, CA Accessory Structures: ADU Rules (2026)

Mendocino County permits Accessory Dwelling Units (ADUs) on parcels with an existing or proposed single-family or multifamily residence, following California's ADU statutes (Gov. Code 66310-66342, formerly 65852.2). Per the County's Planning & Building Services guidance, a detached ADU may be up to 1,200 square feet with its own kitchen, bathroom and bedroom, and an attached ADU may not exceed fifty percent of the existing living area, up to a maximum 1,200-square-foot increase. A Junior ADU (JADU) is no more than 500 square feet, must be within the walls of the existing single-family residence, and requires an efficiency kitchen; state law requires owner-occupancy for a JADU. ADUs must maintain the parcel's required front setback but only a 4-foot side and rear setback. Generally one parking space is required per ADU, waived where the unit is within one-half mile of transit, inside the existing residence, or in other state-exempt situations. The state requires applications to be approved or denied within 60 days when a primary dwelling exists. In the Coastal Zone, ADUs are governed by Coastal Zoning Code Chapter 20.458; a Coastal Development Permit is typically required, the number of coastal ADUs outside the Gualala Town Plan area is limited to 500 units, and water-availability and blufftop standards apply. Verify current rules with Planning & Building Services before designing.