ADU Rules & Regulations in Westbrook, ME
Jan 5, 2026
Last Updated
About
Westbrook, Maine, is a growing city located just west of Portland, known for its strong sense of community, revitalized downtown, and scenic natural beauty. With the Presumpscot River running through the heart of the city, Westbrook offers plenty of outdoor recreation opportunities, including river walks and parks. The city has seen a recent resurgence in both business and cultural activities, with new restaurants, shops, and events bringing a fresh energy to the area. The population was 20,400 at the 2020 census, making it the fastest-growing city in Maine between 2010 and 2020. Combining its industrial roots with modern growth, Westbrook provides a welcoming environment for residents and visitors alike.
ADU Rules
ADUs can be constructed attached to the existing structure, detached, or in an existing accessory structure.
A detached ADU shall share the access drive of the principal structure.
There is only one ADU permitted per lot.
The ADU shall contain a maximum of 800 square feet of habitable (as defined by the building codes) floor area. The floor-to-ceiling height of all habitable floor area shall be a minimum of seven feet. Minimum size of an ADU is 190 square feet.
The owner of the principal structure must reside in either the principal dwelling unit or the ADU. This restriction shall be included in the certificate of occupancy. The ADU shall not be intended for sale and shall remain in common ownership with the principal dwelling unit (single-family dwelling).
Any new construction for an ADU must meet all applicable setbacks, lot coverage, and building height requirements.
For an ADU within or attached to the principal structure, the ADU and the principal structure may be served by a common utility meter.
All ADUs shall be constructed on permanent foundations that meet applicable building codes.
Utility connections - ADUs must be connected to adequate water and wastewater services.
Owner of the ADU must provide written verification that the unit can be connected to adequate potable water and wastewater services.
For potable water: The owner of the ADU must provide proof of access to potable water for a well or approval to connect to a public water source must be provided. For wells, testing may be required to demonstrate water supply is potable and acceptable for domestic use. If the lot is served by public water, both the single-family home and the ADU must be connected to public water.
For wastewater:
If on septic, the septic system on the property in question shall be functioning properly at the time of application for building permit approval.
If on public sewer, the owner must provide proof of access into the public system, additional flow approved and fees paid, as required, by the Wastewater Department. If the lot is served by public sewer, both the single-family home and the ADU must be connected to public sewer.
A detached ADU must share the same driveway as the principal dwelling and be constructed to be visually compatible with principal dwelling.
No additional off-street parking is required for the ADU beyond the requirement of the single-family dwelling unit.
If a short-term rental ordinance is adopted by the City, ADUs will be subject to that ordinance.