Portland, ME Accessory Structures: Garage Conversions (2026)

Portland regulates garage conversions under both the Land Use Code (zoning, parking, ADU standards) and MUBEC (habitability — insulation, egress, smoke alarms, electrical, plumbing). Any conversion of a non-habitable accessory structure (garage) to habitable space triggers a building permit under MUBEC adopted via 25 MRS § 2451. Under the ReCode Land Use Code effective December 4, 2024 (implementing Maine's statewide ADU mandate at 30-A MRS § 4364-B), Portland allows up to two ADUs on a single-family lot, and a converted garage qualifies as a detached ADU. ADU standards under ReCode section 6.6.2 cap detached ADUs at 18 ft in height, or 25 ft if the ADU is positioned above a garage, with ADU floor area limited to two-thirds of the largest principal unit's gross floor area. Required off-street parking lost to a conversion may need to be replaced unless waived; under 30-A MRS § 4364-B, the city cannot impose additional parking requirements specifically for the ADU. Owner-occupancy is NOT required under state law as amended.