Longmont, CO Accessory Structures: Garage Conversions (2026)

A garage conversion in Longmont is a change of occupancy and a substantial alteration under the International Residential Code as adopted in LMC Title 16, so a building permit from Building Inspection is required. The new habitable space must meet code for ceiling height, light, ventilation, egress windows from sleeping rooms, smoke and CO alarms, energy code insulation, and electrical and plumbing if added. If the converted space includes cooking facilities and a separate entrance, it is treated as an accessory dwelling unit and must meet the ADU standards in LMC § 15.02.080.E (allowed zones R-RU, R-SF, R-MN, R-MF, MU-D, N-AG; capped at 800 sq ft or 50% of the principal dwelling; owner-occupancy required; no separate sale; STR prohibited except in qualifying PUDs). If the conversion eliminates required off-street parking for the principal dwelling, replacement parking must be provided on-site — though under HB24-1152, no additional parking can be required for the ADU itself. A garage converted to non-dwelling habitable space (home office, family room, hobby room) still needs a building permit but is not subject to the ADU rules. Conversions that affect the building footprint or move exterior walls must comply with the zoning setbacks in LMC § 15.03.080.C.