Dukes County, MA Accessory Structures: ADU Rules (2026)

Massachusetts ADU law was rewritten by Section 8 of the Affordable Homes Act, signed by Governor Healey on August 6, 2024 as Chapter 150 of the Acts of 2024 (originally House Bill H.4977). The statute amends MGL c. 40A, s.3 to add a new paragraph 11 effective February 2, 2025. Under that paragraph: (1) ADUs are allowed by right (no special permit) in any zoning district that permits single-family use; (2) the ADU may be up to 900 square feet of gross floor area or 50% of the principal dwelling, whichever is less; (3) municipalities may not require owner-occupancy of either unit; (4) municipalities may not require additional parking when the ADU is within 0.5 miles of an MBTA station, commuter-rail station, or ferry terminal, and may require no more than one extra space otherwise; and (5) municipalities retain authority over setbacks, building height, bulk, site-plan review for ADUs that exceed the protected-use envelope, short-term-rental restrictions on ADUs, and the State Building Code (780 CMR). Each Vineyard town has updated its zoning bylaw at its 2025 annual town meeting to comply with the new c. 40A, s.3(11). Edgartown approved an expanded ADU bylaw at the April 2025 annual town meeting that bars short-term-rental use of an ADU and allows a second ADU on a property by special permit through the Edgartown Planning Board. Chilmark approved amendments at its April 2025 annual town meeting that revised ADU definitions and permitted ADUs up to 900 square feet on any qualifying parcel, replacing an older 50%-of-primary-dwelling cap. Tisbury, Oak Bluffs, West Tisbury, and Aquinnah adopted parallel updates at their 2025 town meetings, each adding language that prevents an ADU from being rented as a short-term rental. The Martha's Vineyard Commission, established by Chapter 637 of the Acts of 1974 as amended (the MVC Act), functions as the Vineyard's regional planning agency and reviews Developments of Regional Impact and projects within Districts of Critical Planning Concern under the MVC's DRI Checklist; individual single-family ADUs do not, by themselves, trigger MVC review. However, ADU projects that are part of a larger subdivision or that lie within a designated DCPC (such as the Coastal District, the Roads District, or various town-specific DCPCs) may require MVC referral or sign-off in addition to the local building permit. Properties subject to the Massachusetts Wetlands Protection Act (MGL c. 131, s.40), Title 5 septic (310 CMR 15.000), nitrogen-sensitive watershed limits applicable to much of the Vineyard, and FEMA V/AE coastal flood zones face additional state, local conservation-commission, board-of-health, and floodplain review on top of the by-right ADU zoning entitlement. The town of Gosnold (Cuttyhunk and the Elizabeth Islands) is also part of Dukes County and is subject to the same state ADU statute, although it has very limited zoning capacity and minimal ADU activity.