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

A garage conversion in unincorporated Lassen County is a change of occupancy that requires a building permit reviewed by Lassen County Planning and Building Services for compliance with the adopted California Building, electrical, plumbing, and energy codes (egress, light, ventilation, smoke/CO alarms, and similar life-safety requirements). When the converted garage creates an accessory dwelling unit, California's statewide ADU law (Gov. Code 66310-66342) applies and must be processed ministerially within 60 days. State law is especially permissive for conversions of existing space: an ADU created entirely within an existing accessory structure is generally exempt from the standard ADU height limit, and conversion ADUs are not subject to lot-coverage, front-setback, or design standards that would prohibit them, provided building and health-and-safety codes are met. Lassen County's older 'second dwelling unit' use-permit provision (LCC 18.108.270) is largely superseded by state ADU law for qualifying conversions. If the garage is simply being converted to additional non-dwelling space (a workshop or storage), only the building permit and applicable zoning standards apply. Confirm permit requirements and any parking-replacement questions with the county before starting work.