ADU rules in Wellesley, MA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Wellesley regulates ADUs under Section 5.13 of the Wellesley Zoning Bylaw. At the April 2025 Annual Town Meeting, Wellesley adopted Article 40.1 to amend its ADU bylaw, and the Massachusetts Attorney General approved the changes effective April 15, 2025. As of April 15, 2025, detached ADUs are permitted by-right in Single Residence Districts; a Special Permit is no longer required, consistent with the state Affordable Homes Act.
Under Wellesley Zoning Bylaw §5.13, an ADU is defined as a self-contained housing unit (sleeping, cooking, sanitary facilities) on the same lot as a principal dwelling, with a separate entrance from outside or through a shared entry hall meeting State Building Code (780 CMR) egress requirements, complying with the definition in §1A of M.G.L. c. 40A. The April 2025 amendment removed the Special Permit requirement for detached ADUs in Single Residence Districts, making them by-right with a building permit from the Inspector of Buildings and an annual Certificate of Compliance from the Planning Department. Wellesley aligns with Section 8 of the MA Affordable Homes Act (Chapter 150 of Acts 2024, effective February 2, 2025), which caps ADUs at 900 sq ft or 50% of the primary dwelling, whichever is smaller, and prohibits owner-occupancy and special permit requirements in single-family zones. Bylaw §5.9 (Large House Review) was concurrently amended to integrate ADU thresholds.
Constructing an ADU without a building permit or operating one without the annual Certificate of Compliance from the Wellesley Planning Department is a violation of §5.13 enforced by the Wellesley Inspector of Buildings with stop-work orders, fines up to $300 per day under G.L. c. 40A §7, and required after-the-fact permits or restoration.
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