Portland, Maine
Portland, ME Accessory Dwelling Unit (ADU) Rules
City Acceptance Rating: 10/10
Last Updated: 11.14.2024
Image source: Town of Cape Elizabeth
What You Need To Know
ADUs are permitted in Portland on all legal lots, and on qualifying lots, you can build up to two ADUs.
Type of ADU Permit Required
ADUs are permitted by right through the building department.
ADU Rules
Permitted Locations: ADUs allowed on lawfully conforming and nonconforming lots with legal residential uses.
Types of ADUs: Can be new detached structures, building additions, or within existing structures. Nonconformities cannot increase unless specifically permitted.
Number of Units: Up to two ADUs allowed per qualifying property.
Design Considerations: ADUs in nonconforming structures must prioritize adjacent property privacy.
Size Restrictions:
ADU floor area limited to 2/3 of the largest principal unit's gross floor area.
Total detached ADU square footage cannot exceed the principal structure's gross floor area.
Lot Requirements: Exempt from maximum lot coverage and minimum lot area per dwelling unit requirements.
Height Limits: Detached ADUs limited to 18 feet in height or 25 feet if above a garage.
Setbacks: Subject to side and rear setbacks for accessory structures under 250 square feet.
Placement: Detached ADUs prohibited between the principal structure and front lot line.
Resources:
https://static1.squarespace.com/static/5a75f43a692ebeeb1159413d/t/671025bbe5595f4d699c1994/1729111486146/Final+draft+LUC_10_8_24_compressed_reduced.pdf - pages 91-92 of PDF