ADU rules in Maine
Representative cities: Portland, Lewiston, Bangor.
ADU permit rule
Permit requiredGenerally allowedcity authority
Fee basis
Valuation-based; set by the issuing municipality (no statewide flat fee).
Typical timeline
Plan review typically 2–4 weeks in staffed cities; over-the-counter where pre-approved.
Setback
Per local zoning; shoreland-zone lots have stricter setback rules statewide.
Area threshold
No statewide ADU mandate; size limits set by local ordinance.
Exempt if
None — an ADU (in-law apartment, detached cottage) always requires a building permit where the town enforces MUBEC.
Go / no-go
allowed
Maine has no statewide ADU law. ADUs are allowed only where the local ordinance permits them (e.g., Portland). Verify with your Code Enforcement Officer — many small towns have no ADU provision at all.
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Frequently asked questions
Do I need a permit to build an ADU in Maine?
Per Maine rules, an ADU is "yes" for a permit and the authority is "city". Maine has no statewide ADU law. ADUs are allowed only where the local ordinance permits them (e.g., Portland). Verify with your Code Enforcement Officer — many small towns have no ADU provision at all. Always confirm with the issuing building department.
How big can an ADU be in Maine?
Area threshold: No statewide ADU mandate; size limits set by local ordinance.
What are the ADU setbacks in Maine?
Setback: Per local zoning; shoreland-zone lots have stricter setback rules statewide.
How much does an ADU permit cost in Maine?
Fee basis: Valuation-based; set by the issuing municipality (no statewide flat fee).