ADU Rules in Portland, Maine

Maine does have statewide ADU requirements. The previous version of this page incorrectly said that Portland's ADU policy was governed only locally.

The current state statute is 30-A M.R.S. §4364-B.

Statewide Right to an ADU

Current Maine law requires a municipality to allow an ADU on the same lot as:

• a single-family dwelling unit; or
• a multi-unit structure,

in an area where residential uses are permitted, including as a conditional use.

At least one ADU must be allowed on a lot with a single-family principal structure, subject to the statute and applicable local standards.

Owner Occupancy

Current §4364-B requires municipalities to allow construction or occupancy of an ADU even if the lot owner does not reside in a dwelling on that lot.

Parking

A municipality may not impose an additional ADU parking requirement beyond the parking requirement for the single-family dwelling on the lot.

Minimum Size

State law sets a 190 sq ft minimum ADU size, unless the Technical Building Codes and Standards Board adopts a different minimum.

A municipality may impose a maximum size consistent with state law.

Setbacks

For an ADU within or attached to a single-family dwelling, state law generally requires the same dimensional and setback requirements as the single-family dwelling, subject to the statute's exceptions and more-permissive local standards.

Portland Local Rules

Portland's local zoning code and ReCode framework still control parcel-specific matters that state law leaves to municipalities, including local maximum size, design, shoreland, historic, and other site-specific standards.

Official Sources

Maine 30-A M.R.S. §4364-B — Accessory dwelling units

Portland Zoning Administration

Portland GIS Map Viewer

Disclaimer: Verify Portland's current local standards in addition to the statewide statute before designing an ADU.