Lowell, MA Accessory Structures: Garage Conversions (2026)

The City of Lowell follows the Massachusetts State Building Code (780 CMR), under which a building permit is required to construct, reconstruct, alter, repair, remove or demolish a structure, or to change the use or occupancy of a building or structure. Converting a garage or other accessory structure into habitable living space is a change of use or occupancy and therefore requires a building permit through the City Development Services Office, along with any required plumbing, electrical, and mechanical permits, and the converted space must meet the State Building Code's habitable-space standards. Lowell's ADU framework expressly contemplates converting accessory structures to housing: an Accessory Dwelling Unit may be located 'detached within a new or existing accessory structure on a site (such as a detached garage or carriage house).' Because ADUs are permitted by-right in all zoning districts that allow single-family homes under Section 8 of Chapter 150 of the Acts of 2024 (amending M.G.L. c.40A), a homeowner may convert an existing detached garage or carriage house into an ADU of up to 900 square feet (or 50% of the principal dwelling's gross floor area, whichever is smaller) with a separate entrance and no owner-occupancy requirement, subject to building-permit and code compliance. The converted unit may not be used as a short-term rental, which is prohibited in Lowell.