Maine state law: garage conversions covered by ADU mandate (30-A MRS § 4364-A) and MUBEC change-of-use rules

Conversion of an existing detached or attached garage into livable space (ADU, in-law suite, home office, additional bedroom) in Maine is governed by two layered statutes: (a) If the converted space functions as an accessory dwelling unit, the conversion is covered by the statewide ADU mandate at 30-A MRS § 4364-A (LD 2003 / PL 2021 ch. 672). The municipality SHALL allow at least one ADU per single-family lot, may NOT require owner-occupancy, and may NOT require more than one additional off-street parking space per ADU. (b) Independently, the conversion is a 'change of use' building-code project requiring a building permit under the locally administered Maine Uniform Building and Energy Code (25 MRS § 2451). The local CEO reviews the project for IRC compliance, including: minimum ceiling height (7 feet for habitable rooms per IRC § R305.1); emergency-escape-and-rescue openings (one operable EERO per sleeping room per IRC § R310); window sill height; minimum room area; light and ventilation; Maine Energy Code (IECC) insulation upgrades; smoke and CO alarms per NFPA 72 (interconnected hardwired); electrical service capacity and circuit additions per the National Electrical Code; mechanical heating sufficient to maintain 68°F at design temperature; and plumbing per 22 MRS § 2491 et seq. when a bathroom or kitchen is added. Within the mandatory Shoreland Zone (38 MRS § 435 et seq.), expansion of a nonconforming garage or change of use is constrained by 38 MRS § 439-A (limits on expansion of nonconforming structures within 75 feet of the high-water line — generally capped at 30% total floor-area expansion over the lifetime of the structure when within the setback). Floodplain expansion in mapped Special Flood Hazard Areas triggers floodplain-permit review.

Occupying converted garage space without required permits and inspections is a building-code violation enforceable by the local CEO under 30-A MRS § 4452, with civil penalties typically $100-$2,500 per day plus stop-work and corrective orders. Shoreland-zone violations carry enhanced penalties up to $25,000 per day under 38 MRS § 349.