San Diego County, CA Accessory Structures: Garage Conversions (2026)

In unincorporated San Diego County, converting a garage or other existing permitted accessory structure into living space is most commonly done through the ADU pathway under Section 6156. Per the County PDS-611 handout, no setbacks are required when an existing and permitted accessory structure (or a portion of it) is converted into an ADU, except for fire safety. No additional development standards such as maximum square footage, height, lot coverage, or setbacks apply to the conversion of an existing permitted detached or attached accessory structure into an ADU; the handout notes even a 3,000 sq ft barn could be converted without additional size requirements, subject to fire and building standards for dwelling units. Importantly, parking spaces do not need to be replaced when a garage, carport, or covered parking structure is demolished in conjunction with constructing an ADU or is itself converted into an ADU. Any new addition built onto the converted structure must comply with the standard ADU setbacks (4-foot side/rear) and height limits. The legacy 'second dwelling unit' provisions and the 'accessory apartment' rules in Section 6156 historically required replacement covered off-street parking for garage conversions, but state ADU law now governs.