Modoc County, CA Accessory Structures: Garage Conversions (2026)

Modoc County treats a garage-to-living-space conversion as an accessory dwelling unit under Section 18.100.010(E) of the Zoning Code, which implements state ADU law. The 'converted on single-family lot' provision allows one ADU or JADU within the existing space of an existing single-family dwelling or within the existing space of an accessory structure, plus up to 150 additional square feet if the expansion is limited to accommodating ingress and egress. Such a converted ADU must have exterior access independent of the single-family dwelling and must have side and rear setbacks sufficient for fire and safety as dictated by the building and fire codes. The County's ADU information table confirms that an existing garage or carport may be converted or demolished to make room for a new ADU or JADU, and that replacement parking is not required; if the owner chooses to replace parking, it must meet County parking-space dimension requirements. A JADU created within a single-family residence is capped at 500 square feet and must include an efficiency kitchen, and the primary dwelling must be owner-occupied where a JADU is created. All conversions are approved ministerially by building permit, with the County acting within 60 days, and must still satisfy California Building Code, fire and environmental-health (water and septic) standards. Simply finishing a garage into additional rooms of the main house, rather than creating a separate unit, is a building-permit matter under Title 15.