Santa Clara County, CA Accessory Structures: ADU Rules (2026)

Santa Clara County's Department of Planning and Development regulates accessory dwelling units in unincorporated areas under Zoning Ordinance Section 4.10.015, which the County expressly drafted to be consistent with California ADU law (formerly Government Code Sections 65852.2 and 65852.22, recodified as Government Code Sections 66310-66342). The ordinance states that any County provision conflicting with state law is void and state law applies. Generally, one ADU and one Junior ADU are allowed per legal lot with an existing or proposed single-family residence. Detached ADUs may not exceed 1,200 square feet of floor area, must be set back at least four feet from side and rear lot lines, and may not exceed 16 feet in height unless they meet the single-family residence setbacks (in which case the residential height limit applies). Attached ADUs are capped relative to the primary residence: up to 800 square feet for homes 1,600 square feet or smaller, up to 50 percent for homes between 1,601 and 2,400 square feet, and up to 1,200 square feet for larger homes. Building permit applications are reviewed ministerially and must be approved or disapproved within 60 days of a complete application. ADUs cannot be rented for terms shorter than 30 days and cannot be sold separately from the primary residence.