ADU rules in Scarborough

Detached ADUs are allowed by right wherever dwellings are allowed. Section IX.J.7 lets an accessory dwelling unit be built as a new structure on the lot for the primary purpose of creating an ADU, and Section IX.J.16 adds two siting rules for a detached unit: the structure must sit no more than 100 feet from the nearest point of the principal structure, and it must be designed in the style of a garage, barn, storage building, carriage house, accessory cottage or similar structure customarily found on a single-family lot. A newly built detached ADU must meet the dimensional requirements the town applies to an accessory structure (Section IX.J.9); a unit placed in an accessory building or garage that already existed on July 1, 2023 keeps that building's setbacks (Section IX.J.17). The Section XIII.A combined use tables list Accessory Dwelling Unit, standards at Section IX.J, as P (permitted by right) in all 16 districts where dwellings are allowed.

Internal and attached ADUs are allowed on the same by-right terms. Section IX.J.7 permits a unit within an existing dwelling unit on the lot or attached to or sharing a wall with the single-family dwelling. Section IX.J.15 gives those units the same dimensional and setback requirements as the single-family dwelling itself, so converting a basement or adding a wing does not trigger an accessory-structure setback. Section IX.J.11 requires attached and internal units to preserve the existing streetscape and the single-family appearance and architectural style of the original dwelling; exterior stairways serving an upper-story unit are allowed if integrated into the architecture, but may not be placed on a street-facing side except on a corner lot where no reasonable alternative exists.

Section IX.J.3 caps ADU living space at a percentage of the single-family dwelling's living space or a flat figure, whichever is greater: 40% or 750 sq ft where the house is under 2,000 sq ft; 35% or 750 sq ft from 2,000 to under 3,000 sq ft; 30% or 1,050 sq ft from 3,000 to under 5,000 sq ft; and 20% or 1,500 sq ft where the house is over 5,000 sq ft. The 190 sq ft floor matches the statutory minimum in 30-A M.R.S. §4364-B(6), which also expressly lets a municipality set a maximum. Two related limits bite on the same project: Section IX.J.2 caps occupancy of the ADU at two people, and Section IX.J.8 requires the structure holding the unit to meet the district's lot coverage limits even on a nonconforming lot. There is no separate ADU height cap; height comes from the district standards applied through Section IX.J.9 or .15.

Section IX.J.1 requires the owner or owners of the lot to reside in either the principal structure or the accessory dwelling unit; that residence may be seasonal, which the ordinance defines as any three consecutive months in a twelve-month period. The town states the rule plainly on its ADU page ("Yes, the property owner must reside in either the principal structure or the ADU") and the Accessory Dwelling Unit Application makes the applicant sign an acknowledgment of it. Maine has enacted a preemption of exactly this requirement, 30-A M.R.S. §4364-B(4)(E) (PL 2025, c. 385, §17: a municipality shall allow construction or occupancy of an ADU even if the owner does not reside in a dwelling unit on that lot), but PL 2025, c. 733, §25 (approved April 16, 2026) struck the July 1, 2026 branch of chapter 385's application provision and set the date for all municipalities at July 1, 2027, retroactively to September 24, 2025. Scarborough's requirement is therefore lawful and operative today and becomes unenforceable on July 1, 2027.

The residential parking table in Section XI of the zoning ordinance (table amended 11/19/2025) lists "Accessory Unit: None required," against 1 space per dwelling unit for single-family, two-family and multi-family dwellings. That matches 30-A M.R.S. §4364-B(4)(C), which since the January 1, 2024 implementation date has barred any parking requirement for an ADU beyond the requirement for the single-family dwelling on the lot. The Section VI definition points the same way: an accessory unit approved under Section IX.J is not considered a separate dwelling unit under the zoning ordinance, the subdivision regulations, the growth management ordinance or the impact fee ordinances, so it generates no parking ratio of its own.

Administrative. The Section XIII.A use tables show Accessory Dwelling Unit as P (permitted by right) in every district where dwellings are allowed, with no special exception and no planning board review. Section IX.J puts approval with staff: the Code Enforcement Officer may issue a permit for the construction of an ADU only if it adheres to the listed standards. The town's ADU page says an ADU requires a building permit, and the town publishes a dedicated Accessory Dwelling Unit Application filed with the Code Enforcement Office alongside that permit. The Zoning Board of Appeals only enters the picture if the project needs a dimensional break: Section IX.J.13 lets an ADU applicant also apply for a Limited Reduction of Yard Size under Section V.B.5. ADUs are exempt from the district's density and lot-area requirements (Section IX.J.4) and from Scarborough's rate of growth permit system (Section IX.J.5).

Section IX.J.1 provides that neither the accessory dwelling unit nor the single-family dwelling shall be rented for less than 28 continuous days, and the town's FAQ reads that as a flat ban: either structure may be rented as a full-time or seasonal residence, but neither may be a short-term rental. Chapter 1020, the Short-Term Rental Registration Ordinance adopted May 20, 2026, states the same rule from the other direction: short-term rentals are not permitted in accessory dwelling units nor in the dwelling on the same lot as an ADU approved under Section IX.J. So Scarborough's new short-term rental framework (registration with the Town Clerk, registration deadline December 31, 2026 and the requirement effective January 1, 2027, plus new owner-occupied and non-owner-occupied STR uses and a Coastal Beach Zone overlay added to the zoning ordinance on 05/20/2026) does not open ADUs to short-term use. The unit also cannot be sold off on its own: Section VI provides that an approved Section IX.J unit is not a separate dwelling unit under the zoning ordinance or the Scarborough Subdivision Regulations.