ADU rules in Lowell

Detached backyard ADUs are allowed by right. Lowell has not written its own ADU ordinance, so the city administers the Massachusetts protected-use rule directly: its ADU Guide devotes a section to detached ADUs and states they may be new freestanding structures or conversions of an existing detached structure such as a garage or carriage house. Lowell's un-amended zoning text still points the other way (Section 4.3.7(2) bars using an accessory building as a dwelling except as allowed by Article XIII(n), and Article XIII(n) permits an ADU only in the Urban Single-Family district and only by special permit), but that text is unenforceable as to a Protected Use ADU: 760 CMR 71.03(2)(e) makes any requirement that an ADU be attached or detached a Prohibited Regulation. A new detached ADU must still meet the accessory-structure dimensional rules the city applies (Sections 4.3.5 and 4.4.1), including the 16 foot height limit in residential districts.

Internal and attached ADUs are allowed by right on the same terms. The city's ADU Guide treats internal ADUs (carved out of the existing footprint, with no floor area added) and attached ADUs (an addition built to hold the unit) as two of the three permitted forms, and requires attached ADUs to meet the ordinary dimensional regulations in Section 5.1 of the zoning ordinance for the district. The state definition in M.G.L. c. 40A sec. 1A requires a separate entrance, either directly from outside or through an entry hall or corridor shared with the principal dwelling that satisfies the building code for safe egress. Lowell imposes no extra local hurdle for the internal or attached form.

Lowell applies the state floor without adding a smaller local cap: the ADU Guide states the maximum size is 900 square feet or 50% of the gross floor area of the principal dwelling, whichever is smaller. Gross floor area is measured under 760 CMR 71.02, which counts all stories of compliant ceiling height including basements and lofts but excludes crawl spaces, garage parking areas, attics and enclosed porches. Height is the binding constraint for many detached units: Section 4.4.1(1) caps an accessory building in a residential district at 16 feet above ground level, and Section 4.4.1(2) lets garages and outbuildings with no more than one story of habitable space rise to match the primary dwelling's roof pitch but never exceed the primary dwelling's height. Detached units must also sit at least 10 feet from the principal building and 5 feet from any side or rear lot line under Section 4.3.5(4); attached units follow the Section 5.1 dimensional table for the district.

No owner occupancy is required, at application or on an ongoing basis. Lowell's ADU Guide answers the question flatly: there is no owner-occupancy requirement for either the principal dwelling or the ADU. That mirrors M.G.L. c. 40A sec. 3, para. 11, which states that use of land or structures for an ADU shall not require owner occupancy of either unit, and 760 CMR 71.03(2)(a), which lists an owner-occupancy requirement as a Prohibited Regulation. Lowell's zoning ordinance never contained an ADU owner-occupancy condition to begin with, so there is no stale local text on this point.

Lowell's ADU Guide states that no off-street parking may be required for an ADU if the property is within 0.5 miles of a transit station, and it expressly counts bus stops. That reading tracks 760 CMR 71.02, which defines a Bus Station as a location serving as a point of embarkation for any bus operated by a transit authority, so Lowell Regional Transit Authority stops qualify alongside the MBTA Lowell Line commuter rail station at Gallagher Terminal; in a city of Lowell's density that leaves very little land outside the radius. Where a lot is entirely outside every 0.5 mile radius, 760 CMR 71.03(2)(b)(1) still caps the requirement at one additional space. The generic zoning requirement of 2 spaces per dwelling unit in Section 6.1.4 cannot be applied to a protected ADU.

A first ADU is ministerial: apply to the Division of Development Services for a building permit, with zoning review handled administratively by staff. The city's ADU page opens by stating that ADUs under 900 square feet are allowed by right in all zoning districts that allow single-family homes, and Lowell has adopted no local special permit, site plan review or design review process for them. M.G.L. c. 40A sec. 3, para. 11 forbids requiring a special permit or other discretionary zoning approval for a single ADU in a single-family residential zoning district, and 760 CMR 71.03(1) repeats the bar. Practice matches: at the June 22, 2026 Zoning Board of Appeals hearing on 24 Staples Street the chair noted the ADU could not be considered in that variance petition and the applicant confirmed the ADU was already covered by an active building permit.

Lowell's ADU Guide states that ADUs may be rented and there are no restrictions on who the property can be rented to, then warns that short-term rentals are not allowed anywhere in the City of Lowell and that all residential rental units must be rented for a minimum of thirty days. The prohibition is structural rather than express: the zoning use table has no short-term rental entry, and Section 12.11(a) provides that a use not covered by the table cannot be varied or authorized by the Board of Appeals in any district. 760 CMR 71.03(3)(c) expressly permits municipalities to prohibit short-term rental of a protected ADU, so this restriction is enforceable, and the state law measures a short-term rental by the M.G.L. c. 64G definition (stays of not more than 31 consecutive calendar days). Nothing in Lowell's rules limits who may occupy the unit, and 760 CMR 71.03(2)(c) bars occupancy restrictions based on income, age, family relationship or student status.