ADU rules in Portland, ME — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Portland permits up to two accessory dwelling units (ADUs) per qualifying residential lot under Land Use Code Chapter 14 §6.6.2 (the December 2024 ReCode), implementing the statewide ADU mandate in 30-A MRS §4364-B.
Portland's Land Use Code (Chapter 14 of the Code of Ordinances), as comprehensively rewritten through the ReCode effective December 4, 2024, governs ADUs at Section 6.6.2. Up to two ADUs are permitted per qualifying property containing a legal residential use, on conforming and lawfully nonconforming lots. Each ADU is capped at two-thirds of the gross floor area of the largest principal dwelling unit on the lot. Detached ADUs may not exceed 18 feet in height (or 25 feet if located above a garage), and must remain clearly subordinate in scale and position to the principal structure when visible from a public way. Above-ground-floor exterior stairways and fire escapes are prohibited on ADU facades that face a public way. Side and rear setbacks for ADUs were substantially reduced in ReCode — rear setbacks of 5 feet and side setbacks of 3 to 5 feet apply in most residential zones. The state ADU mandate at 30-A MRS §4364-B requires that municipalities allow at least one ADU on lots where single-family dwellings are permitted, bars municipalities from imposing parking requirements beyond what the principal unit requires, and exempts one ADU from any density calculation. Portland's two-ADU allowance exceeds the state floor.
Building a structure as an ADU without a building permit, or exceeding the size, height, or setback standards of §6.6.2, is a zoning violation subject to a stop-work order and civil penalties of up to $2,500 per day under 30-A MRS §4452 (the statutory cap on municipal civil-violation fines for land-use enforcement). Non-conforming construction must be brought into compliance or removed; the ADU may be denied a Certificate of Occupancy until corrected.
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