Portland, ME Accessory Structures: Tiny Homes (2026)

Maine state law (25 MRS § 2451 et seq. — MUBEC) governs the building code for tiny homes, and 30-A MRS § 4364-B establishes the minimum tiny-ADU floor area at 190 sq ft. The Portland Permitting & Inspections Department applies MUBEC to all permanent dwellings: a tiny home on a permanent foundation, meeting MUBEC's structural, energy, egress, and life-safety standards, is treated as a single-family dwelling or — more commonly — as a detached ADU under ReCode Land Use Code section 6.6.2 (effective December 4, 2024). As an ADU it must meet Portland's height (18 ft detached, 25 ft above a garage) and setback (3-5 ft side/rear residential) standards, with floor area limited to two-thirds of the largest principal unit's gross floor area. Tiny houses on wheels (THOWs) are not recognized as permanent dwellings under MUBEC and are treated by Portland as recreational vehicles — they cannot be occupied as permanent residences on residential lots and are subject to Portland's RV/camping prohibitions. Tiny homes built off-site as modular construction must be certified to Maine's modular building program under 10 MRS § 9041 et seq. and are then treated the same as site-built homes for zoning. Portland has issued guidance acknowledging that the biggest obstacle to tiny homes is the statewide building code, which the city is required to enforce.