Accessory Structures in Lowell, MA

If you live in Lowell or are thinking about moving there, accessory structures are one of those things you probably won't think about until they affect you directly. Lowell has 3 specific rules on the books covering different aspects of accessory structures, and some of them might surprise you.

Shed & Carport Rules

In Lowell, storage sheds over 200 square feet require a building permit; sheds up to 200 square feet and 16 feet tall may sit within side and rear yard setbacks but must stay at least 10 feet from the dwelling and be anchored against wind.

Key details: Authority: City of Lowell Development Services; MA State Building Code. Permit threshold: Building permit required over 200 sq ft. Permit-light size/height: Up to 200 sq ft and 16 ft tall. Distance from dwelling: At least 10 ft. Setback placement: May sit within side and rear yard setbacks.

A shed over 200 square feet (or any shed with utility connections) built without a building permit can be cited under code enforcement, requiring an after-the-fact permit, proper frost-depth footings, or removal/relocation if it violates the 10-foot separation from the dwelling. A shed placed too close to the dwelling or improperly anchored may be ordered corrected.

Garage Conversions

Per the Massachusetts State Building Code, a building permit is required to change the use or occupancy of a structure, so converting a Lowell garage or accessory building to living space needs a permit; converting an existing detached structure to an ADU is allowed by-right under state ADU law.

Key details: Authority: MA State Building Code (780 CMR); City of Lowell Development Services. Permit trigger: Change of use/occupancy requires a building permit. ADU conversion: Detached garage/carriage house may become an ADU by-right. ADU size cap: 900 sq ft or 50% of principal dwelling GFA, whichever is smaller. State law: M.G.L. c.40A; Ch. 150, Acts of 2024, S.8.

Converting a garage or accessory structure to living space without a building permit, or without changing the recorded use/occupancy, is a violation of the Massachusetts State Building Code and can result in stop-work orders, after-the-fact permit fees, and an order to either legalize the space to code or restore the original non-habitable use. Code-enforcement action may also follow if the conversion is operated as a prohibited short-term rental.

ADU Rules

Lowell allows one accessory dwelling unit by-right on any lot that permits single-family homes, capped at 900 square feet or 50% of the principal dwelling's gross floor area (whichever is smaller), with no owner-occupancy requirement, under Massachusetts's statewide ADU law.

Key details: State law: M.G.L. c.40A S.1A & S.3; Ch. 150, Acts of 2024, S.8. State regulation: 760 CMR 71.00. Permitting: By-right in single-family districts. Max ADU size: 900 sq ft OR 50% of principal dwelling GFA, whichever is smaller. Allowed types: Internal, external (addition), or detached.

Building or occupying an ADU without the required building, plumbing, and electrical permits can trigger code-enforcement action, stop-work orders, and after-the-fact permit fees, and the unit must be brought into compliance with the Massachusetts State Building Code before it can be legally occupied. Operating an ADU as a prohibited short-term rental can result in zoning enforcement under the City's short-term-rental prohibition.

Lowell is more permissive than most cities when it comes to adu rules. That said, there are still limits.

The Bottom Line

Lowell's accessory structures rules are a mixed bag. Some areas are strict, others are relaxed, and the details matter. The best approach is to check the specific rule that applies to your situation rather than assuming Lowell is broadly strict or permissive.

These rules come from Lowell's publicly available municipal code. For complete penalty schedules, exemption details, and answers to common questions, see the individual ordinance pages throughout this guide.