Leominster, MA Accessory Structures: ADU Rules (2026)
ADU rules in Leominster, MA, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- Right to build
- One ADU by right in Residential districts
- Size cap
- 900 sq ft or half main home's area
- Parking
- 1 added space unless near transit
- Driveway
- No new driveway/curb cut allowed
- Grandfathering
- Pre-9/12/2005 ADUs if permitted
- Adopted
- 2-25-26, aligned with state Affordable Homes Act
Summary
Leominster allows one accessory dwelling unit by right in any Residential district under Article XV of the zoning ordinance, adopted February 25, 2026. An ADU is capped at 900 square feet or half the principal home's floor area, whichever is smaller, and generally needs one added off-street parking space.
90.1The owner of a principal residential dwelling may construct an accessory dwelling unit by right as an accessory residential use in a Residential district provided that each of the following criteria are met:90.1.1Only one accessory dwelling unit may be created on a lot with a principal residential structure.90.1.2Adequate provision must be made for the disposal of sewage, waste and drainage generated by the occupancy of the entire dwelling, including the ADU, in accordance with the requirements of the Leominster Department of Public Works and Board of Health.90.1.3The accessory dwelling unit must have a gross floor area no greater than nine hundred square feet, or half the gross floor area of the principal residential structure, whichever is smaller.90.1.4Unless located within one-half mile of a transit or bus station, at least one off-street parking space must be provided for each accessory dwelling unit, in addition to the parking for the principal dwelling. No new driveway or curb cut may be created to service the ADU.90.1.5The construction of an accessory dwelling unit must be in conformity with state building code requirements.90.1.6A permit issued for an accessory dwelling unit on a lot with a principal residential structure does not authorize apartment, multi-family, or two-family dwelling use of the subject premises.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Code of Ordinances: Supplement 24).
Full Breakdown
Effective under a February 25, 2026 amendment that repealed and replaced the prior accessory-apartment article, Sec. 1 lets the owner of a principal residential dwelling build one accessory dwelling unit by right as an accessory residential use in a Residential district, provided several conditions are met. Only one ADU may be created per lot with a principal residential structure (Sec. 1). Sewage, waste and drainage for the whole property, ADU included, must satisfy the Department of Public Works and Board of Health (Sec. 2). The unit's gross floor area cannot exceed nine hundred square feet, or half the gross floor area of the principal residential structure, whichever is smaller (Sec.
3). Unless the lot sits within a half mile of a transit or bus station, the owner must provide at least one off-street parking space for the ADU on top of the parking required for the principal dwelling, and no new driveway or curb cut may be built to serve it (Sec. 4). Construction must meet the state building code (Sec. 5), and an ADU permit does not authorize converting the property to a two-family or multi-family use (Sec. 6). Section 22-91 flags septic capacity as a separate area of concern for lots not on municipal sewer, urging owners to check with the Board of Health before drawing plans.
Section 22-92 grandfathers any ADU that already existed in a single-family home as of September 12, 2005, so long as it was built under a permit or is recognized by the assessor's office. This ordinance was rewritten in 2026 to align with the state's Affordable Homes Act, which now requires municipalities statewide to allow a protected ADU by right in single-family zones; Leominster's by-right structure, 900-square-foot cap and reduced parking trigger reflect that state floor rather than a separate, more restrictive local scheme.
Violations & Fines
Building an ADU without a permit, exceeding the 900-square-foot/half-floor-area cap, adding a second ADU on the same lot, or cutting a new driveway where none is allowed under Sec. 22-90.1.4 violates Article XV and the zoning ordinance's general penalty in Sec. 22-15: up to $300 per violation, with each day counted separately, enforced by the director of inspections, who may also withhold occupancy or building permits under Sec. 22-7 and Sec. 22-8.
Frequently Asked Questions
Do I need a special permit to build an ADU in Leominster?
How big can a Leominster ADU be?
Does my ADU need its own parking space?
Sources & Official References
Other rules in Leominster
How Leominster compares: Easiest Cities to Build an ADU·Compare Leominster to another location·View the Massachusetts accessory structures overview
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ADU Rules in Nearby Cities
How other cities in this county handle adu rules.