Garage conversion rules in Somerville, MA — sometimes called garage-to-ADU or accessory living unit conversions — govern permits, ceiling height, egress, and parking replacement.
Converting a garage to living space in Somerville requires a building permit and may qualify as an ADU under the 2024 Affordable Homes Act with relaxed zoning review.
A garage conversion changes the use of an existing accessory structure into conditioned habitable space, which under the Massachusetts State Building Code requires full compliance with energy code, egress, ceiling height, fire separation, and ventilation standards. In Somerville, a building permit is required, along with plumbing, electrical, and mechanical permits as applicable. If the conversion creates a separate dwelling unit, it qualifies as an ADU and can proceed by right under MGL c.40A s.3A up to 900 square feet, without a special permit. If the garage conversion is simply expanded primary dwelling space, it is treated as an addition. Parking minimums in Somerville have been largely eliminated, so losing a garage stall typically does not trigger variance review.
Contact your local code enforcement office for specific penalty information.
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Side-by-side rule comparisons with other cities in Middlesex County.
See how other cities in Middlesex County handle garage conversions.
See how Somerville's garage conversions rules stack up against other locations.
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