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Accessory Dwelling Units (ADUs) in Maine: rules in 19 towns compared
Can I build an ADU (in-law apartment, guest house, garage apartment)? Here's how each town answers it. Click a town for the details and the exact ordinance text.
Last reviewed
This page is for Maine homeowners thinking about an in-law apartment, garage apartment or backyard cottage. Under 30-A M.R.S. §4364-B, every town must allow at least one accessory dwelling unit (ADU) on a lot with a single-family home anywhere homes are allowed. It can be inside the house, attached or detached. One ADU per lot is exempt from density limits, towns can't require parking beyond what the house already needs, and you must show adequate water and septic or sewer before anyone moves in. Starting July 1, 2027, towns can no longer require the owner to live on the property or require planning board approval for an ADU.
All 19 towns we cover allow ADUs, and most approve them through the Code Enforcement Officer. Eight of them (Gorham, Harpswell, Kennebunk, Kittery, North Yarmouth, Ogunquit, Rockport and Scarborough) still have an owner-occupancy rule on the books. Fixed size caps range from 600 sq ft in Camden to 1,200 sq ft in Cape Elizabeth and South Portland, and other towns use a share of the main home's floor area instead. Cape Elizabeth, Kennebunk, Ogunquit, South Portland and York don't allow the ADU to be used as a short-term rental. Pick your town below for the details and the ordinance text.
Town-by-town comparison
| Town | Verdict | Short answer |
|---|---|---|
| Cape Elizabeth | Allowed with a permit | Yes. Cape Elizabeth allows one accessory dwelling unit on any lot where a single-family home is the principal structure, inside the house, attached, or in a separate building. It can be no more than 1,200 sq ft (and smaller than the main home) and must meet a minimum size (190 sq ft in the ordinance, which defers to the state building codes board's standard, set at 160 sq ft in 2025); it can't be used as a short-term rental, and you need a building permit from the Code Enforcement Officer. |
| Yarmouth | Allowed with board review | Yes. Accessory Dwelling Units are a permitted use in Yarmouth's residential districts (RR, LDR, MDR and others), and they can be inside, attached to, or detached from a single-family home. An ADU is approved under the town's separate Site Plan Review Ordinance (Chapter 702), which holds the detailed ADU standards we did not review. |
| Cumberland | Allowed with a permit | Yes. Cumberland allows one accessory dwelling unit, attached or detached, with a single-family home or multifamily structure on any lot in any zoning district, approved by the Code Enforcement Officer through an ADU permit. The ADU must meet the district's setbacks and the Plumbing Inspector must confirm adequate septic or sewer capacity. |
| North Yarmouth | Allowed with a permit | Yes. North Yarmouth allows one accessory dwelling unit on a lot with a single-family home, approved by the Code Enforcement Officer, in every district except Resource Protection. The ADU can be inside, attached or detached, is limited to one bedroom and 40% of the main house's living area, and the owner must live in either the ADU or the main house. |
| Freeport | Allowed with a permit | Yes. Freeport allows one ADU on a lot with a single-family home (or one or two single-family homes, or a duplex). It can be inside the house, an addition, in an accessory building that already existed on January 1, 2024, or a new detached building that meets the house setbacks. It can be no larger than 1,100 sq ft or 75% of the main home's floor area, whichever is smaller, and no smaller than 190 sq ft. You need a building permit and a Certificate of Occupancy from Codes Enforcement. |
| Scarborough | Allowed with a permit | Yes. Scarborough allows one accessory dwelling unit per single-family home in all residential zones with a permit from the Code Enforcement Officer. The owner must live on the property, the ADU must be at least 190 sq ft (max generally 750 sq ft or a percentage of the house, whichever is greater), occupancy is limited to two people, and no extra parking is required. |
| South Portland | Allowed with a permit | Yes. South Portland permits one accessory dwelling unit (ADU) per lot in every residential zone, inside the house, as an attached addition, or as a detached building, with a permit from the Code Enforcement Officer. On lots under 10,890 sq ft the ADU can be up to 800 sq ft (or 90% of the main home, if smaller), no extra parking is required, and an ADU approved under the current rules cannot be used as a short-term rental. |
| Portland | Allowed with a permit | Yes. Portland allows up to two ADUs on any lot with a legal residential use. An ADU can be inside the house, an addition, or a new detached building, and it can be up to 2/3 the size of the main unit. Detached ADUs can be 18 feet tall (25 feet over a garage), can't sit between the house and the front lot line, and need no parking. You'll need a building permit; we found no owner-occupancy requirement in the Land Use Code. |
| Gorham | Allowed with a permit | Yes. Gorham calls ADUs "accessory apartments." One is allowed on any lot where a single-family home is allowed or exists, with Code Enforcement Officer approval. It can be attached or detached, must be 190 to 800 sq ft, and the owner must live on the property. |
| Harpswell | Allowed with a permit | Yes. Harpswell allows one accessory dwelling unit on any lot with a single-family home, inside the house, attached, or in a separate building, without extra lot area. The ADU can be up to 750 sq ft, the owner must live in either the house or the ADU, and it needs a Code Enforcement permit plus proof the septic system can handle both units. |
| Brunswick | Allowed with a permit | Yes. Brunswick allows one accessory dwelling unit per lot on single- or two-family residential lots, inside the house, attached, or in a detached building, without Development Review. The ADU can be no larger than 1,100 sq ft or 75% of the main home's floor area, whichever is less, and you need a permit backed by proof of adequate water and wastewater. |
| Topsham | Allowed | Yes. According to a Topsham Codes Office handout (we could not review the zoning ordinance text itself), an ADU is allowed as long as it meets the standards in Section 225-54 of the Zoning Ordinance. Under the 2021 building code, a unit with its own complete living facilities inside a single-family house generally makes the building a two-family dwelling, so expect to meet two-family construction standards. |
| Kennebunk | Allowed | Yes. Kennebunk lists the accessory dwelling unit as a permitted use in its residential districts. It can be inside, attached to, or detached from a single-family home. One ADU is allowed per single-family lot, sized between 190 and 1,000 sq ft, and the owner must live in either the house or the ADU. The ADU can't be used as a short-term rental. |
| York | Allowed with a permit | Yes. York allows one accessory dwelling unit (ADU) per single-family lot in every zone, inside the house, attached, or in a detached accessory building. You need a building permit and an occupancy permit from the Code Enforcement Officer, and no Planning Board approval. The ADU can be no larger than 850 sq ft or 50% of the main house's floor area, whichever is smaller, and no short-term rentals are allowed anywhere on a lot with an ADU. |
| Kittery | Allowed with a permit | Yes. The 2022 version of Kittery's Title 16 we reviewed allows one accessory dwelling unit per single-family lot in residential zones like R-S. If it meets the standards, the Code Enforcement Officer can approve it without a board hearing. The ADU can be up to 1,000 sq ft with no more than two bedrooms, and it can't be rented to the same party for less than 30 days. |
| Ogunquit | Allowed with board review | Yes. Under the 2023 rewrite of Ogunquit's ADU section, you can add one accessory dwelling unit, attached or freestanding, to a single-family home. It must be 190 to 700 sq ft, the main house must be owner-occupied, and you need Design Review approval and a certificate of occupancy before anyone moves in. |
| Camden | Allowed with a permit | Yes. Camden calls an ADU an "accessory apartment": one unit of 600 sq ft or less on a lot with a single-family home, allowed in the Rural 1 and 2, Coastal Residential, Village Extension and Traditional Village districts, among others. Both units must be someone's primary residence, the apartment needs one parking space, and you need a building permit from the Code Enforcement Officer. Our copy of the zoning ordinance only runs through June 2022, so confirm the current rules. |
| Rockport | Allowed with a permit | Yes. Rockport allows one accessory dwelling unit on any lot where a single-family home is the principal building, inside the house, attached, or as a new detached building, with a building permit from the Code Enforcement Officer. The ADU must be at least 190 square feet, a detached one can't be taller or larger than the main house, and the ordinance currently requires the owner to live in either the house or the ADU. |
| Mount Desert | Allowed with a permit | Yes. On a lot with a single-family home outside the Shoreland Zone, Mount Desert allows one accessory dwelling unit with a Code Enforcement Officer permit, and you don't need extra lot area for it. It can be inside the house, attached, or in a new building, and must be at least 190 sq ft but no more than 75% of the main home's living area. |
Maine's statewide ADU law
Under 30-A M.R.S. §4364-B (first passed as LD 2003 in 2022), a town must allow at least one accessory dwelling unit (ADU) on a lot with a single-family home anywhere homes are allowed. Towns had to comply by 2024.
Rules in effect now:
- It can be inside the house, attached, or a new detached building.
- One ADU per lot is exempt from density limits.
- No extra parking can be required beyond what the house already needs.
- Setbacks are the same as for the house.
- Minimum size: the state building codes board set 160 sq ft in 2025. Towns may set a maximum size.
- Before you can move in, you must show the ADU has adequate water and septic/sewer.
- In the shoreland zone ADUs must meet shoreland rules, but towns can't ban them there outright.
- Sprinklers aren't required unless the ADU is in or attached to a building with more than 2 units.
Coming July 1, 2027 (LD 1829 of 2025, pushed back by LD 2173 in 2026): towns can no longer require the owner to live on the property, ADUs must also be allowed next to 2- and 3-unit buildings, and towns can't require planning board approval for an ADU. Towns may still regulate short-term rentals in ADUs. Private covenants and HOA rules can be stricter.
Common questions about adu rules in Maine
- What is the ADU law in Maine?
- Maine's ADU law (30-A M.R.S. §4364-B, first passed as LD 2003 in 2022) requires every town to allow at least one accessory dwelling unit on a lot with a single-family home wherever homes are allowed. It can be inside the house, attached or detached. One ADU per lot is exempt from density limits, and towns had to comply by 2024.
- Can my town require me to live on the property to build an ADU in Maine?
- For now, yes. Starting July 1, 2027, state law bars towns from requiring the owner to live on the property. That change was originally passed in 2025 and pushed back by a 2026 law. Until then, a town's owner-occupancy rule can still apply. Private covenants and HOA rules can be stricter than state law.
- Do I need extra parking for an ADU in Maine?
- No. Under state law, a town can't require more parking for an ADU beyond what the single-family home already needs. If your town's parking table seems to require more, ask the code office how it applies to ADUs.
- How small or large can an ADU be in Maine?
- The state building codes board set a 160 sq ft minimum in 2025. There's no statewide maximum: towns may set their own. In the towns we cover, fixed caps range from 600 sq ft (Camden) to 1,200 sq ft (Cape Elizabeth and South Portland), and some towns cap the ADU at a percentage of the main home instead.
- Can I build an ADU in the shoreland zone in Maine?
- Yes, as long as it meets the shoreland zoning rules, such as water setbacks and lot coverage limits. State law says towns can't ban ADUs in the shoreland zone outright. Setbacks from property lines are the same as for the house.
- Can I rent my ADU on Airbnb in Maine?
- It depends on your town. State law lets towns keep regulating short-term rentals in ADUs, even after the July 1, 2027 owner-occupancy change. Several towns we cover, including Cape Elizabeth, Kennebunk, Ogunquit, South Portland and York, don't allow an ADU to be used as a short-term rental.
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