Town Permit Guide

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Can I build an ADU in Duxbury, Massachusetts?

Duxbury, Plymouth County · Bylaws checked 2026-10-03 · Reviewed · 10 cited sections

Allowed with a permit

Yes. Duxbury's zoning bylaw allows one attached or detached ADU per lot with a single-family home. It can be no larger than half the main home's floor area or 900 sq ft, whichever is smaller. You need a building permit, one parking space, and a ban on rentals under 31 days. An ADU in a newly built structure also needs site plan review with a public hearing.

Number allowed1 ADU per lot (attached or detached) [3]
Max sizeSmaller of 900 sq ft or 1/2 the main home's gross floor area [2]
Parking1 space (none if within 0.5 mile of a transit station) [4]
Minimum rental term31 days; short-term rentals prohibited on the lot [5]
Site plan reviewRequired for an ADU in a newly constructed structure, with public hearing [6]
Owner-occupancyNot required by the bylaw [1]

These rules come from Duxbury's zoning bylaw as compiled through the June 2025 Special Town Meeting; later Town Meetings may have changed them.

Where and what

Section 410.6 of the Protective (Zoning) Bylaw allows one "Protected Use ADU" per principal dwelling in single-family residential districts, following the state ADU law [1]. The ADU may be attached or detached, and only one ADU per lot qualifies [3]. It must have its own sleeping, cooking and bathroom facilities and a separate entrance. It can be no larger than half the main home's gross floor area or 900 sq ft, whichever is smaller [2]. The ADU can't be sold or conveyed separately from the main house [9]. The bylaw doesn't require the owner to live on the property.

Parking, rentals and septic

One parking space is required unless the ADU is within 0.5 miles of a transit station [4]. If either the ADU or the main house is rented, the minimum term is 31 days. Short-term rentals are prohibited, and advertising a stay under 31 days counts as a violation [5]. Before the Building Commissioner issues a permit, you need a Board of Health sewage disposal works permit where applicable [8]. The Board of Health must also certify in writing that sewage disposal is adequate.

Site plan review for new buildings

An ADU in a newly constructed structure or building needs site plan review [6]. That includes a public hearing with notice to abutters [7] and a plan stamped by an engineer or surveyor. The plan must cover screening, lighting, and decks or balconies facing neighbors. The bylaw requires this review only for ADUs in newly built structures, but Sec. 410.6(10)(b) says no permit issues until "the ADU has undergone the Site Plan Review process," so ask the Building Department whether a conversion inside an existing house needs it too.

Nonconforming houses

If your house or lot doesn't conform to zoning and the ADU would increase that nonconformity, no special permit is needed. The Zoning Board of Appeals must still find that the change is not substantially more detrimental to the neighborhood.

Notes

Section 410.3 still lists a special-permit "conversion" of a 10-year-old house "in accordance with Section 410.6" [10]. That appears to be leftover wording from an older accessory-apartment rule. State law bars towns from requiring a special permit for a protected ADU.

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

Next steps

  1. Confirm with the Building Department (781-934-1100 ext. 6002) that your lot is in a single-family district and check the ADU size limit against your home's gross floor area.
  2. Get Board of Health sign-off on septic capacity (a sewage disposal works permit if the system must change).
  3. For a new detached or newly built ADU, file for site plan review (engineer- or surveyor-stamped plan); a public hearing with abutter notice will be scheduled.
  4. Apply to the Building Commissioner for a building permit with a plot plan; if near wetlands, contact the Conservation Commission first.

Common questions

Can I build an ADU in Duxbury, Massachusetts?
Yes. Duxbury's zoning bylaw allows one attached or detached ADU per lot with a single-family home. You need a building permit, and an ADU in a newly built structure also needs site plan review with a public hearing.
How big can an ADU be in Duxbury, Massachusetts?
An ADU can be no larger than half the main home's gross floor area or 900 sq ft, whichever is smaller.
Does an ADU need parking in Duxbury, Massachusetts?
Yes, one space, though none is needed if the ADU is within 0.5 mile of a transit station.
Can I rent my ADU on Airbnb in Duxbury, Massachusetts?
No. On a lot with an ADU, neither the ADU nor the main house may be rented for less than 31 days, and short-term rentals are prohibited on the lot.

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 Duxbury's published bylaws. Section numbers are as printed in the source.

  1. Sec. 410.6, Protective (Zoning) Bylaws, amended through June STM 2025, p. 55
    To achieve this goal and to promote the other objectives of this bylaw one Protected Use ADU per Principal Dwelling may be allowed in accordance with the specific standards set forth below for such accessory use.
  2. Sec. 410.6 (Definitions, Accessory Dwelling Unit), Protective (Zoning) Bylaws, amended through June STM 2025, p. 55
    b. is not larger in Gross Floor Area than ½ the Gross Floor Area of the Principal Dwelling or 900 square feet, whichever is smaller; and
  3. Sec. 410.6 (Definitions, Protected Use ADU), Protective (Zoning) Bylaws, amended through June STM 2025, p. 56
    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 protected by M.G.L. c. 40A, § 3, provided that only one ADU on a lot may qualify as a Protected Use ADU.
  4. Sec. 410.6(1), Protective (Zoning) Bylaws, amended through June STM 2025, p. 56
    1. One parking spot shall be required for the Protected Use ADU unless the Protected Use ADU is within 0.5 miles of a Transit Station.
  5. Sec. 410.6(7), Protective (Zoning) Bylaws, amended through June STM 2025, p. 57
    7. Minimal Rental Period: Where the ADU or the Principal Dwelling is occupied as a rental unit, the minimum occupancy or rental term shall be 31 or more days and Short Term Rentals as defined by G.L. 64G shall be prohibited. Advertisement of any form for less than 31 days shall be conclusive evidence of a violation of this sub-section.
  6. Sec. 410.6(8), Protective (Zoning) Bylaws, amended through June STM 2025, p. 57
    8. Site Plan Review. Notwithstanding the provisions of Section 615, Site Plan Review as outlined below shall be required for all Protected Use ADUs in a newly constructed structure or building.
  7. Sec. 410.6(8)(a), Protective (Zoning) Bylaws, amended through June STM 2025, p. 57
    a. A public hearing with notification to abutters per Chapter 40A Section 11 shall be required.
  8. Sec. 410.6(10)(b), Protective (Zoning) Bylaws, amended through June STM 2025, p. 58
    No permit shall be issued until a sewage disposal works permit, when applicable, has first been obtained from the Board of Health and the proposed building and location thereof conform with the town’s bylaws.
  9. Sec. 410.6(5), Protective (Zoning) Bylaws, amended through June STM 2025, p. 56
    5. Legal Ownership: The Protected Use ADU shall be accessory and not be legally separated or conveyed apart from the Principal Dwelling in order to keep the accessory nature of the ADU.
  10. Sec. 410.3(3), Protective (Zoning) Bylaws, amended through June STM 2025, p. 52
    3. Conversion of a single-family dwelling in existence for ten (10) years prior to the application for a special permit in accordance with Section 410.6.
This page summarizes Duxbury's posted bylaws as of 2026-10-03. Bylaws are amended, and individual lots can have overlays, subdivision covenants, or HOA rules that are stricter. Confirm with Building Department (Building Commissioner / Director of Municipal Services) (781-934-1100 ext. 6002 (Building Dept); ext. 5481 (Building Commissioner)) before you build. Spot an error?