Portland, ME Accessory Structures: ADU Permits (2026)

Portland's Permitting and Inspections Department enforces the Maine Uniform Building and Energy Code (MUBEC) under 25 MRS §2451 et seq., which applies in Portland because the city's population substantially exceeds the 4,000-person threshold for mandatory MUBEC enforcement. Any ADU project — whether converting an existing attic, basement, garage, or accessory building into habitable space, or constructing a new detached ADU — requires a building permit before work begins. Trade permits (electrical, plumbing, mechanical/HVAC) must be filed separately under the relevant Maine licensing statutes (32 MRS §1311 et seq. for electrical; 22 MRS §2491 et seq. for plumbing). The Department directs ADU applicants to apply online through its e-permitting portal. Zoning review under Land Use Code §6.6.2 is performed as part of the building-permit intake; the project must satisfy the dimensional standards (height, setback, size cap at 2/3 of principal unit), and a deed restriction may be required at Certificate of Occupancy keeping the ADU and at least one other on-site dwelling unit under common ownership. ADUs are permitted by right — no Planning Board or Board of Appeals action is required if standards are met.