Grass Valley, CA Accessory Structures: Garage Conversions (2026)

A garage conversion to an accessory dwelling unit in unincorporated Nevada County is reviewed ministerially through the County Planning Department, consistent with California State ADU Law (Gov. Code 66310 et seq.). Two key state protections apply directly to garage conversions. First, a local agency may not require the replacement of off-street parking spaces that are eliminated when a garage, carport, or covered parking structure is converted to an ADU (Gov. Code 66314). Second, an ADU created entirely within the existing space of a permitted garage or accessory structure may not be subjected to new setback requirements, because the structure already exists in its location; the standard 4-foot side and rear setback the County references applies to new construction rather than to interior conversions of legal structures. A JADU (junior ADU, up to 500 sq ft) may also be created within an existing single-family residence, and the County may not require parking as a condition of a JADU, even when it is converted from an attached garage (Gov. Code 66334). A building permit is still required for the conversion to verify life-safety, egress, and habitability standards. As with all ADUs, a completed application is deemed approved if the County does not act within 60 days (Gov. Code 66317).