Town Permit Guide

Home › Massachusetts › Westford › Accessory Dwelling Units (ADUs)

Can I build an ADU in Westford, Massachusetts?

Westford, Middlesex County · Bylaws checked 2026-10-19 · Reviewed · 11 cited sections

Allowed

Yes. In Westford's residential districts (RA and RB) one Protected Use ADU, attached or detached and no larger than 900 sq ft or half the main house's floor area (whichever is smaller), is allowed by right. A larger Local ADU of over 900 up to 1,250 sq ft needs a special permit from the Zoning Board of Appeals, plus an owner-occupancy affidavit. These rules come from the certified zoning bylaw the town posted in April 2026.

Protected Use ADU max size900 sq ft or half the principal dwelling's gross floor area, whichever is smaller [1]
Protected Use ADU approval (RA, RB)Allowed by right (Y) [2]
Protected Use ADU parkingAt most 1 space; none within 0.5 mile of a transit station [3]
Local ADU approvalSpecial permit from the Board of Appeals [4]
Local ADU sizeOver 900 sq ft up to 1,250 sq ft, not larger than the main house's floor area or footprint [5]
Local ADU owner occupancyAffidavit that one unit is owner-occupied at least 6 months each year [6]
Local ADU parkingAt least 1 space [7]
Site plan reviewADUs are exempt [8]

Two kinds of ADU

Westford's zoning bylaw, as amended at the October 27, 2025 Special Town Meeting (Article 4), now has two categories. The rules here are from the certified bylaw the town posted in April 2026; we did not find the Attorney General's approval letter itself.

An ADU is a self-contained unit with its own sleeping, cooking and sanitary facilities and a separate entrance; it may be detached, attached, or inside the main house [9].

Protected Use ADU (by right)

A Protected Use ADU is no larger than half the main house's gross floor area or 900 sq ft, whichever is smaller, and only one per lot can qualify [1]. The Table of Accessory Use Regulations allows it by right (Y) in the RA, RB, B, IA, IB and IC districts [2]. The town may require no more than one parking space, and none within half a mile of a transit station [3]. It must comply with Title 5 septic rules [1]. No owner-occupancy rule applies to this type.

Local ADU (special permit)

A bigger Local ADU needs a special permit from the Zoning Board of Appeals [4]. It may be larger than 900 sq ft but not over 1,250 sq ft, and not larger than the main house's floor area or footprint; it can be in the main house or a detached accessory building [5]. The application needs a surveyor's certified plot plan, floor plans and elevations, and an affidavit that one of the units is owner-occupied at least six months each year [6]. At least one parking space is required [7]. A new owner must file an affidavit within 90 days of a sale or the permit ends. The ZBA has discretion and can say no. Because a Local ADU is larger than what state law protects, the owner-occupancy rule here doesn't conflict with the state ADU law.

Other reviews

ADUs, protected or by special permit, are exempt from site plan review [8]. Both types still have to meet the building code, Title 5 septic rules, wetlands rules and zoning dimensional requirements, per the town's January 2026 ADU presentation [10]. The town's ADU page also confirms the Special Town Meeting vote [11], though that page is out of date and still says the final bylaw is "to be published soon".

See how Westford compares with 8+ other Massachusetts towns on accessory dwelling units (adus) →

Next steps

  1. Check your zoning district and lot setbacks with the Building Department (978-692-5527); confirm the ADU fits 900 sq ft or half your home's floor area to qualify by right.
  2. Talk to the Board of Health about septic (Title 5) capacity before designing; the town strongly advises this for Local ADUs.
  3. For a Protected Use ADU, apply for a building permit with plans and a certified plot plan.
  4. For a Local ADU (900 to 1,250 sq ft), apply to the Zoning Board of Appeals for a special permit with a certified plot plan, floor plans/elevations and the owner-occupancy affidavit.
  5. If the work is within 100 feet of a wetland, get Conservation Commission approval first.

Common questions

Can I build an ADU in Westford, Massachusetts?
Yes. One Protected Use ADU, attached or detached and no larger than 900 sq ft or half the main house's floor area (whichever is smaller), is allowed by right in Westford's RA and RB districts. A larger Local ADU needs a special permit from the Zoning Board of Appeals. These rules come from the certified zoning bylaw the town posted in April 2026.
How big can an ADU be in Westford, MA?
It depends on the type. A by-right Protected Use ADU can be up to 900 sq ft or half the main house's gross floor area, whichever is smaller. A Local ADU may be over 900 sq ft but not over 1,250 sq ft, and no larger than the main house's floor area or footprint; it needs a Zoning Board of Appeals special permit.
Does the owner have to live on the property to have an ADU in Westford, Massachusetts?
No, not for a Protected Use ADU; no owner-occupancy rule applies to that type. For a larger Local ADU, the special permit application needs an affidavit that one of the units is owner-occupied at least six months each year, and a new owner must file an affidavit within 90 days of a sale or the permit ends.
How many parking spaces does an ADU need in Westford, MA?
For a Protected Use ADU, Westford may require no more than one parking space, and none within half a mile of a transit station. A Local ADU, which needs a special permit, must have at least one parking space.
Do I need a permit to build an ADU in Westford, Massachusetts?
Yes. A Protected Use ADU needs a building permit with plans and a certified plot plan, but no special permit, and ADUs are exempt from site plan review. Both types must meet the building code, Title 5 septic rules, wetlands rules and zoning dimensional requirements.

Massachusetts' statewide ADU law

Since February 2, 2025, the Affordable Homes Act (St. 2024, c. 150, §8) has protected one accessory dwelling unit (ADU) per lot in any zoning district that allows single-family homes (M.G.L. c. 40A, §3). Your town cannot ban it, require a special permit or other discretionary approval, or "unreasonably restrict" building or renting it.

What counts as a protected ADU:

  • A self-contained unit with its own sleeping, cooking and bathroom facilities, on the same lot as the main home.
  • No larger than 900 sq ft or half the main home's floor area, whichever is smaller.
  • It can be attached or detached, and it needs a separate entrance that meets the building code.

What towns cannot require:

  • That the owner live in the main home or the ADU.
  • More than 1 extra parking space, or any extra space if the lot is within 0.5 miles of a subway, commuter rail, ferry or bus station.
  • A minimum lot size, caps on the number of ADUs, or limits on who may live there (age, income, relationship).

What towns can still do: use reasonable site plan review, setback, height and bulk rules, require Title 5 septic compliance, and restrict or ban short-term rentals of ADUs. A second ADU on the same lot needs a special permit. State regulations at 760 CMR 71.00 (in effect since January 31, 2025) explain which rules count as unreasonable.

State sources: M.G.L. c. 40A, §3 (protected ADU paragraph) · M.G.L. c. 40A, §1A (ADU definition) · EOHLC, Accessory Dwelling Units (law, FAQ, 2026 draft regulations) · 760 CMR 71.00, Protected Use Accessory Dwelling Units

What the bylaw says

Exact text from Westford's published bylaws. Section numbers are as printed in the source.

  1. Sec. 10.2, definition of Protected Use ADU, 2025 Zoning Bylaw (amended through Special Town Meeting October 27, 2025; certified copy), p. 197
    Protected Use ADU: An attached or detached ADU that is located, or is proposed to be located, on a Lot in a Single-Family Residential Zoning District and is not larger in Gross Floor Area than ½ the Gross Floor Area of the Principal Dwelling or 900 square feet, whichever is smaller, provided that only one ADU on a Lot may qualify as a Protected Use ADU.
  2. Appendix B, Table of Accessory Use Regulations, A.14, 2025 Zoning Bylaw (amended through Special Town Meeting October 27, 2025; certified copy), p. 217
    14. Protected Use Accessory dwelling unit Y Y Y N N N Y Y Y N
  3. Appendix D, Table of Parking Requirements, F, 2025 Zoning Bylaw (amended through Special Town Meeting October 27, 2025; certified copy), p. 225
    For Protected Use Accessory Dwelling Units, not more than one (1) parking space may be required; however, no parking spaces are required for Protected Use ADUs located within a 0.5-mile radius of a Transit Station.
  4. Sec. 3.3.2 Special Permit Required, 2025 Zoning Bylaw (amended through Special Town Meeting October 27, 2025; certified copy), p. 22
    Local accessory dwelling units may be allowed by special permit by the Board of Appeals, subject to the following considerations:
  5. Sec. 3.3.4(1) Limit, 2025 Zoning Bylaw (amended through Special Town Meeting October 27, 2025; certified copy), p. 23
    Not more than one local accessory dwelling unit may be established on a lot. The local accessory dwelling unit may be larger than 900 square feet but may not exceed 1,250 square feet of gross floor area and shall not exceed the gross floor area or footprint of the primary dwelling unit.
  6. Sec. 3.3.3(4) Affidavit, 2025 Zoning Bylaw (amended through Special Town Meeting October 27, 2025; certified copy), p. 22
    4. Affidavit. Certification by affidavit shall be provided that in every calendar year one of the dwelling units shall be occupied by the owner of the property for at least six months.
  7. Sec. 3.3.4(3) Parking, 2025 Zoning Bylaw (amended through Special Town Meeting October 27, 2025; certified copy), p. 23
    Sufficient and appropriate space for at least one (1) parking space shall be provided by the owner to serve the local accessory dwelling unit.
  8. Sec. 9.4.2(4) Exemptions from site plan review, 2025 Zoning Bylaw (amended through Special Town Meeting October 27, 2025; certified copy), p. 179
    b. Accessory dwelling units, whether protected use or subject to a special permit;
  9. Sec. 10.2, definition of Accessory Dwelling Unit, 2025 Zoning Bylaw (amended through Special Town Meeting October 27, 2025; certified copy), p. 184
    ADUs may be detached, attached, or internal to the Principal Dwelling.
  10. ADU 101 slideshow, slide 9, ADU 101: Learn, Plan, Build (slideshow, January 16, 2026), p. 9
    Must meet Title V requirements, State Building Code requirements, State and Local Wetlands Requirements, and zoning dimensional requirements
  11. Accessory Dwelling Units - ADUs page, Accessory Dwelling Units - ADUs (Town information page), p. 1
    At Special Town Meeting 2025, the town voted to amend the ADU bylaw to be compliant with the updated state law (final bylaw to be published soon).
This page summarizes Westford's posted bylaws as of 2026-10-19. Bylaws are amended, and individual lots can have overlays, subdivision covenants, or HOA rules that are stricter. Confirm with Building Department (Building Commissioner & Zoning Enforcement Officer Erik Tardif), Town Hall, 55 Main Street, Westford MA 01886 (978-692-5527) before you build. Spot an error?