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

Sierra County Code (SCC) 15.10.030, adopted by Ordinance 1133 (effective January 2, 2025), implements California's ADU statutes (Gov. Code 66310 et seq.). ADUs are allowed by right in any zone allowing residential uses and are approved ministerially through the building permit process, which must be acted upon within 60 days of a complete application. The code allows two ADUs and one junior ADU (JADU) per parcel that has an existing or proposed single-unit dwelling. A detached ADU may not exceed 1,200 square feet of floor area, and is limited to 16 feet in height (18-20 feet near major transit, or up to 25 feet for an ADU above a detached garage). Standard interior side, street side and rear setbacks are four feet; no setback is required where an existing structure or garage is converted, except as needed for fire and safety. Where lot coverage would otherwise preclude an ADU, the county must allow at least one 800-square-foot unit. One off-street parking space is required per ADU or bedroom (whichever is less), with numerous state-mandated exemptions (within a half-mile of transit, conversions, historic properties). Junior ADUs are capped at 500 square feet, must be within the walls of the primary dwelling, require owner occupancy, and need no parking. A recorded deed restriction is required for JADUs.