Cumberland County, ME Accessory Structures: ADU Rules (2026)

Cumberland County government has no zoning code and does not regulate accessory dwelling units. ADU rules in the county's 28 municipalities (Portland, South Portland, Westbrook, Scarborough, Gorham, Brunswick, Falmouth, Windham, Cape Elizabeth, Freeport, etc.) are set by each town's land use ordinance, but they must comply with the statewide ADU floor created by LD 2003 (PL 2021, ch. 672) and codified at 30-A MRS § 4364-B. The statute directs that 'at least one accessory dwelling unit must be allowed on any lot where a single-family dwelling unit is the principal structure' in any zone that permits a single-family home. An ADU must meet a minimum size of 190 square feet (30-A MRS § 4364-B). Municipalities may still apply dimensional standards (setbacks, lot coverage, height) that match the primary dwelling's standards and may set a maximum ADU size, but may not prohibit ADUs in single-family zones, may not require owner occupancy, and may not impose ADU-specific parking demand. The Maine Shoreland Zoning Act (38 MRS § 435 et seq.) still applies within 250 feet of great ponds, rivers, tidal waters, and freshwater wetlands — a major overlay across Cumberland County's Casco Bay coast, Sebago Lake, and Presumpscot River corridor. The Maine Uniform Building and Energy Code (MUBEC, 25 MRS § 2451) applies to ADU construction in every Cumberland County municipality (all exceed the 4,000-population enforcement threshold).