Grass Valley, CA Accessory Structures: ADU Rules (2026)

L-II 3.19 (Accessory and Second Dwelling Units) and L-II 3.19.1 (Accessory and Junior Accessory Dwelling Units) bring the County code into alignment with current state ADU law. By state-mandated minimums the County must allow at least an 850 sq ft attached or detached ADU (1,000 sq ft for a two-bedroom unit) and a Junior ADU up to 500 sq ft within an existing single-family home. The County applies a 5-foot minimum side and rear setback per state law for new construction, and ADUs above an existing garage or accessory structure also follow that 5-ft minimum. Height limits follow state defaults (16-25 ft depending on configuration). The County may not require replacement parking when a garage or carport is converted to an ADU. Owner-occupancy of the primary dwelling is not required for an ADU but is required for a JADU. ADUs permitted after April 25, 2019 carry a recorded deed restriction prohibiting short-term rentals (rentals of less than 30 days). Building permits in the unincorporated SRA include CAL FIRE Chapter 7A review for ignition-resistant construction.