ADU rules in Brunswick

Detached backyard ADUs are permitted by right. Zoning Ordinance Sec. 3.4.2.A(3) allows an ADU on lots primarily used as single or two family residential 'in either a principal or detached structure', and Tables 3.2 and 3.3 mark 'Accessory dwelling unit' as 'P', which Sec. 3.1.1.A defines as permitted by-right, in every district where a 1- or 2-family dwelling is itself permitted: all nine Growth Residential districts (GR1 through GR9), the Growth Mixed-Use districts other than GM7, the Growth Commercial districts, and the rural RF, RR, RP1, RP2 and RM districts. Only one ADU is allowed per lot, and it is exempt from density calculations (Sec. 3.4.2.A(2), (4)). A detached ADU may not exceed the height of the principal structure unless it is constructed above a garage and meets all applicable dimensional standards (Sec. 3.4.2.A(7)).

Internal and attached ADUs stand on exactly the same footing as detached ones. The definition in Sec. 1.7 covers a self-contained unit with living, cooking and bathroom facilities 'located within, attached to, or detached from a single- or two-family dwelling', so basement conversions, additions and units carved out of the existing house all qualify. Section 3.4.2.A(3) permits the ADU in the principal structure with no extra approval step, and the same by-right 'P' designation in Tables 3.2 and 3.3 applies. The only condition aimed at attached units is Sec. 3.4.2.A(5): where reasonably practicable, the ADU entrance must be on a different façade than the existing or primary dwelling unit's.

Section 3.4.2.A(6) caps the ADU at 1,100 square feet or 75 percent of the gross floor area of the largest dwelling unit, whichever is less, so the percentage test governs on smaller houses: a 1,200 sq ft home yields a 900 sq ft cap, while homes above roughly 1,467 sq ft run into the flat 1,100 sq ft ceiling. Garage or carport floor area used by the ADU is excluded from the ADU's square footage total, which makes garage conversions and above-garage units noticeably more workable. Height is capped separately: a detached ADU may not exceed the principal structure's height unless it sits above a garage and meets all dimensional standards (Sec. 3.4.2.A(7)). Maine sets a 190 square foot statutory floor and expressly permits municipalities to impose a maximum (30-A M.R.S. § 4364-B(6)), so Brunswick's ceiling is lawful.

Brunswick imposes no owner-occupancy requirement. A full-text search of the zoning ordinance turns up residency language only in the Bed and Breakfast definition and in disability-accommodation provisions, never for ADUs. The single ownership rule is Sec. 3.4.2.A(9), 'An ADU must be owned by the owner of the principal structure and may not be a condominium unit', which compels common ownership and blocks separate sale but says nothing about who lives on the lot, so an absentee owner may build and rent an ADU today. Brunswick is therefore already ahead of 30-A M.R.S. § 4364-B(4)(E), the statewide bar on municipal owner-occupancy requirements, which does not bind any Maine municipality until July 1, 2027 under PL 2025, c. 385, § 23 as amended by PL 2025, c. 733, § 25.

No off-street parking is required for an ADU. Table 4.9.1.A sets the household-living minimum for 'Dwelling, 1- or 2-family (includes all mobile homes; excludes accessory dwelling units)' at 2 spaces per unit, or 1 for a studio or one-bedroom, and that parenthetical carves ADUs out of the requirement entirely; no other section of the ordinance supplies an ADU parking standard. This matches 30-A M.R.S. § 4364-B(4)(C), which bars any additional parking requirement beyond the primary dwelling's and has bound Brunswick since its implementation date of January 1, 2024, the date 30-A M.R.S. § 4364(1-A)(A) assigns to municipalities whose ordinances the municipal officers enact without voter approval.

Administrative review only. An ADU is a 'P' use, defined by Sec. 3.1.1.A as permitted by-right, wherever a 1- or 2-family dwelling is permitted, and Sec. 3.4.2.A(1) states flatly that 'An ADU does not require Development Review', so no Planning Board hearing is involved. The owner files for a Building Permit with the Code Enforcement Officer and receives a Certificate of Occupancy on completion (Sec. 5.2.1.A), using the town's online permit portal. Before any permit issues the applicant must provide written verification from qualified professionals of an adequate and safe water supply and adequate wastewater connection (Sec. 3.4.2.A(8), implementing 30-A M.R.S. § 4364-B(7)). Two narrow geographies add a discretionary step: inside the Airport Approach Zone an ADU is a 'C' use requiring a Conditional Use Permit (Table 2.3.7), and work in the Shoreland Protection Overlay needs an SPO permit under Sec. 5.2.6.

Nothing in the zoning ordinance limits renting an ADU, and Brunswick has no short-term rental cap, license or primary-residence test; the only lodging licence is the innkeeper's licence for inns, hotels, motels and bed and breakfasts under Code § 10-26. What does apply is the rental registry at Code ch. 8, art. III, whose definition of 'Rental unit' says in terms that 'Short term rents and ADUs are subject to this ordinance'. Owners must register with the Fire Department Fire Prevention Office by January 15 each year beginning in January 2026, update within 90 days of a transfer or change of manager, and no certificate of occupancy issues for a property that is subject to the requirement and unregistered (§§ 8-103, 8-106). A unit rented to a member of the owner's immediate family is exempt from registration. Separately, Zoning Ordinance § 3.4.2.A(9) requires the ADU to be owned by the owner of the principal structure and forbids condominium units, so it cannot be sold off on its own.