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

Under California state ADU law, which preempts most local restrictions, Riverside County must ministerially approve ADUs up to 850 sq ft (1,000 sq ft for 2+ bedrooms) in the rear/side yard with 4-foot setbacks, and must approve conversion ADUs (within an existing home or accessory structure) with no setback or lot coverage restriction. A JADU up to 500 sq ft within the existing walls of a single-family home is also allowed, with a deed-restricted owner-occupancy requirement for either the JADU or the primary dwelling. SB 1211 (effective January 2025) increased the cap on detached ADUs on multifamily lots from 2 to 8 (up to 25% of existing units). AB 2533 (2024) expanded legalization pathways for unpermitted ADUs built before 2020 by limiting code corrections to health-and-safety items. Riverside County Planning reviews ADU applications ministerially (no CEQA, no public hearing) and must act within 60 days of a complete application. Impact fees are capped: ADUs under 750 sq ft pay no impact fees; larger ADUs pay fees proportional to their size relative to the primary dwelling. Owner-occupancy requirements for standard ADUs were suspended through 2025 under AB 881. Short-term rental (< 30 days) of ADUs is prohibited under state law.