Garage conversion rules in Wellesley, MA — sometimes called garage-to-ADU or accessory living unit conversions — govern permits, ceiling height, egress, and parking replacement.
Wellesley allows garage conversions to ADUs under Wellesley Zoning Bylaw §5.13 (as amended April 15, 2025 by Article 40.1) consistent with Section 8 of the Massachusetts Affordable Homes Act. Converted garage ADUs are by-right in Single Residence Districts with a building permit from the Inspector of Buildings and an annual Certificate of Compliance from the Planning Department.
Under Wellesley Zoning Bylaw §5.13, an existing detached or attached garage may be converted to an ADU by-right in Single Residence Districts (no Special Permit required as of April 15, 2025). The converted unit must not exceed 900 sq ft or 50% of the gross floor area of the primary dwelling (whichever is smaller), must have a separate entrance, and must meet the State Building Code (780 CMR) for ceiling height, egress windows, light and ventilation, smoke and CO alarms, and fire separation between units. Wellesley Inspector of Buildings issues the building permit; HVAC, plumbing, and electrical sub-permits are required separately. The Planning Department issues an annual Certificate of Compliance verifying continued ADU status. The existing garage's setbacks are typically grandfathered for the conversion footprint; any added square footage beyond the original walls must meet underlying-zone setbacks. The April 2025 amendment also revised §5.9 Large House Review thresholds to coordinate with ADU floor area.
Converting a Wellesley garage to habitable space without a building permit is a violation of the State Building Code (780 CMR) and §5.13, with stop-work orders, fines up to $300 per day under G.L. c. 40A §7, and required after-the-fact permits or restoration. Failing to renew the annual Certificate of Compliance is separately citable by the Planning Department.
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