Lowell, MA Accessory Structures: ADU Rules (2026)

Lowell permits Accessory Dwelling Units (ADUs) by-right in all eleven zoning districts that allow single-family homes (SSF, SMF, SMU, TSF, TTF, TMF, TMU, USF, UMF, UMU, DMU), pursuant to Section 8 of Chapter 150 of the Acts of 2024 (the Affordable Homes Act), which amended M.G.L. c.40A, S.3 and added the ADU definition to M.G.L. c.40A, S.1A. An ADU is a small, self-contained residential living space on the same lot as a principal dwelling, and may be internal (within the existing structure), external (an addition), or detached (in a new or existing accessory structure such as a detached garage or carriage house). The maximum size for an ADU is 900 square feet OR 50% of the gross floor area of the principal dwelling, whichever is smaller. Each ADU must maintain a separate entrance, either directly from the exterior of the home or through an entry hall. There is no owner-occupancy requirement for either the principal dwelling or the ADU, and the ADU may be rented as a long-term unit. However, short-term rentals (STRs) are not allowed in the City of Lowell, so an ADU cannot be operated as a short-term rental. No off-street parking may be required for an ADU if the property is located within 0.5 miles of a transit station, consistent with state regulation 760 CMR 71.00. Protective ADUs (those built by-right under state law) must comply with the State Building Code and local building, plumbing, and electrical permitting administered by the City Development Services Office.