Maine’s accessory-dwelling-unit (ADU) statute directs municipalities to allow an ADU on the same lot as a single-family dwelling unit or a 2-unit or 3-unit residential structure in areas where residential uses are permitted, including as a conditional use. It also requires at least one ADU to be allowed on a lot whose principal structure is a single-family dwelling unit or a 2-unit or 3-unit residential structure, and exempts one ADU from density calculations. Both rules are subject to statutory qualifications. This is a state framework with implementation and property limits, not blanket approval for a particular lot.

Owner residence is not a condition of the state allowance

The statute says a municipality must allow ADU construction or occupancy even if the lot owner does not reside in a dwelling on the lot. That provision does not by itself decide private covenants, funding terms, rental licences, landlord-tenant obligations, or whether an existing unit has the required permits. Separate rules can apply to a particular program or private instrument.

The statute identifies allowed placement forms, refers to implementation timing, and includes a watershed exception. Water supply, wastewater, local zoning, building and fire approval, and the unit’s prior status may affect the result. Do not assume that the density exemption eliminates those independent requirements.

Verify timing and the parcel

Before relying on the law for construction, occupancy, or rental, check the current version of 30-A M.R.S. § 4364-B and its implementation-date cross-reference, the municipality’s current code, and whether the property is subject to the watershed exception. Confirm water and septic eligibility, existing permit or legalization records, and any private title or association restrictions with the responsible offices.

The statute describes what municipalities must allow within its scope; it does not determine a parcel’s zoning, safe occupancy, or rental status. The broader owner-occupancy overview compares Maine’s framework with other state and local rules.