San Benito County, CA Accessory Structures: ADU Rules (2026)

San Benito County Code § 25.08.002 (Accessory Dwelling Units and Innovative Housing) governs ADUs in unincorporated areas and tracks California Government Code §§ 66310-66342. On a single-family parcel you may build one attached or detached ADU and one junior ADU (JADU). Detached ADU size standards follow state law; an attached ADU is limited to 50% of the primary dwelling or 1,500 sq ft, whichever is less, while JADUs are capped at 500 sq ft and must be within the walls of the primary dwelling. New-construction ADUs require only a 4-foot rear and interior side setback under state law, and conversions of legally existing structures are exempt from those setbacks. Detached ADUs may reach 16 feet, with greater heights near transit or for two-story contexts per state defaults. The County also publishes free pre-approved ADU building plans through its Building & Code Enforcement Division to encourage construction. Because state law preempts conflicting local rules, applications are processed ministerially within statutory timeframes; the County cannot impose owner-occupancy on a standard ADU but may require it for a JADU. Given fast residential growth and large ranch parcels, ADUs on agriculturally zoned land must still meet septic, water, and access requirements verified by the Resource Management Agency.