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Can I build an ADU in Sandwich, Massachusetts?

Sandwich, Barnstable County · Bylaws checked 2026-10-20 · Reviewed · 11 cited sections

Allowed with a permit

Yes. Sandwich's zoning bylaw (Section 4130, as rewritten by the May 2025 Town Meeting; we used the town's May 2025 printed edition) allows one accessory dwelling unit inside, attached to, or detached from a single-family home by right in all residential districts, with a building permit. The ADU can be no larger than half the house or 900 sq ft, whichever is smaller, needs one extra off-street parking space, and can't be a short-term rental; if rented, leases must be at least 12 months. No owner-occupancy, special permit or yearly permit cap applies.

Allowed whereBy right in all residential districts (within, attached to, or detached from a single-family home) [1]
Max size1/2 the main home's gross floor area or 900 sq ft, whichever is smaller [2]
Parking1 extra off-street space (none if within 0.5 mile of a transit station) [3]
Short-term rentalNot allowed; rentals by lease of at least 12 consecutive months [4]
Before the building permitSite plans and elevations of exterior changes [5]
Penalty$100 per offense; each day is a separate offense [6]
Older accessory apartment option (Sec. 4115)Max 800 sq ft, 1 bedroom, owner-occupied, non-rental [8]
Owner occupancy, special permit, yearly capNot required (deleted by the May 2025 Town Meeting vote) [9]

What the bylaw allows

Under Section 4132, an ADU within a single-family dwelling, attached to it, or detached, on a lot conforming to Section 2600, is a "By Right" use in all residential districts [1]. The use table allows ADUs in R-1, R-2, VIL, BL-1, B-2, RD and S, but not in FLEX, IND, MAR or GD. The Building Commissioner administers the section, and ADUs aren't eligible for variances.

Size, parking and design

An ADU is a self-contained unit with its own sleeping, cooking and sanitary facilities and a separate entrance, subject to site plan review. It can be no larger than half the main house's gross floor area or 900 sq ft, whichever is smaller [2]. You need one extra off-street parking space unless the ADU is within 0.5 mile of a transit station [3]. It must be clearly subordinate to the house and can't be sold separately. Site plans and elevations are due before the building permit [5].

Rentals

Neither the house nor the ADU may be used for boarding, lodging or short-term rentals. A rented ADU needs a lease of at least 12 consecutive months [4]. Violations carry a $100 fine per day [6]. The town's short-term rental bylaw (Ch. 12) also bars ADUs from STR registration.

The older accessory apartment (Sec. 4115)

The bylaw still prints a separate "By-Right Accessory Apartment": a non-rental unit in an owner-occupied home [7], max 800 sq ft and one bedroom [8].

What the May 2025 vote changed

Town Meeting rewrote Section 4130 on May 5, 2025, 318 to 57 [9]. The vote deleted the old limit of 24 by-right permits a year, the special permit and 20,000 sq ft lot for detached ADUs, the 2-bedroom limit, the owner-occupancy rule and affidavit, and the amnesty clause. None of those are in the bylaw now. The vote also struck "on a lot conforming to Section 2600," but the printed bylaw still contains it [1]. Ask the Building Department which text it applies. A November 2025 proposal for larger "Expanded" ADUs failed [10].

State law

Massachusetts law protects one ADU per lot by right and bars minimum lot size rules, so it may override the printed lot-conformity condition. Towns may restrict or ban short-term rentals of ADUs. Whether a 12-month minimum lease goes further than allowed isn't settled. State housing officials have proposed rule changes, not final as of October 2026, that would treat lease minimums over 32 days as going too far. North of Route 6, exterior work is also reviewed by the Old King's Highway Historic District Committee [11].

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

Next steps

  1. Email setbacks@sandwichmass.org or call the Building Department (508-888-4200) to confirm your lot's district and setbacks.
  2. Prepare site plans and elevations showing the exterior changes and the extra parking space, plus a floor plan showing the ADU's size (no more than half the house or 900 sq ft).
  3. Apply for the building permit online through Permit Eyes; Title 5 septic capacity must also be approved.
  4. If the property is north of Route 6, get a Certificate of Appropriateness from the Old King's Highway Historic District Committee (Planning & Development, 508-833-8001) for exterior changes.

Common questions

Are ADUs allowed in Sandwich, Massachusetts?
Yes. Sandwich's zoning bylaw (Section 4130, May 2025 edition) allows one accessory dwelling unit inside, attached to, or detached from a single-family home by right in all residential districts, with a building permit. No owner-occupancy, special permit or yearly permit cap applies. One open question: the printed bylaw still says the lot must conform to Section 2600, though the May 2025 vote struck that phrase. Ask the Building Department.
How big can an ADU be in Sandwich, MA?
An ADU in Sandwich can be no larger than half the main home's gross floor area or 900 sq ft, whichever is smaller. It also needs one extra off-street parking space, unless it's within 0.5 mile of a transit station.
Can I use an ADU as an Airbnb in Sandwich, Massachusetts?
No. Sandwich's bylaw bars short-term rentals of both the house and the ADU, and the town's short-term rental bylaw makes ADUs ineligible. If the ADU is rented, the lease must be at least 12 consecutive months. Proposed state rule changes, not final as of October 2026, could affect lease minimums like this.
Does the owner have to live on the property to build an ADU in Sandwich, MA?
No. The May 2025 Town Meeting vote deleted Sandwich's owner-occupancy rule for ADUs, along with the special permit and the yearly permit cap, and state law protects one ADU per lot. The town's separate, older accessory apartment option (Section 4115) is the one that requires an owner-occupied home.
What do I need to get an ADU permit in Sandwich, Massachusetts?
You need a building permit, applied for online through Permit Eyes. Submit site plans and elevations of the exterior changes before the permit is issued, and Title 5 septic capacity must be approved. North of Route 6, exterior work also needs Old King's Highway Historic District Committee approval.

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

  1. Sec. 4132(a) Requirements, Protective Zoning By-law (May 2025 edition), p. 37
    An ADU constructed within a single family dwelling, attached to a single family dwelling or as a detached structure on a lot conforming to Section 2600 of the Zoning By-Law shall be permitted as a “By Right” use in all residential districts.
  2. Definitions, Accessory Dwelling Unit, Protective Zoning By-law (May 2025 edition), p. 84
    is not larger in gross floor area than 1/2 the gross floor area of the principal dwelling or 900 square feet, whichever is smaller;
  3. Sec. 4133(c), Protective Zoning By-law (May 2025 edition), p. 38
    At least one (1) off street parking space in conformance with the Town’s driveway regulations in addition to that required for the principal single-family dwelling is required for each ADU unless the ADU is located within 0.5 miles from a transit station.
  4. Sec. 4133(e), Protective Zoning By-law (May 2025 edition), p. 38
    The primary dwelling and ADU shall not be used for boarding and lodging, or other commercial uses including but not limited to, short-term rentals. When rented, no occupancy of the ADU is permitted other than by lease for a minimum of twelve (12) consecutive months and other conditions as stated.
  5. Sec. 4132(e), Protective Zoning By-law (May 2025 edition), p. 38
    Prior to the issuance of a building permit for an ADU, site plans, and elevations shall be submitted showing the proposed exterior changes to existing buildings or new building and improvements on a lot associated with a proposed ADU.
  6. Sec. 4134 Enforcement, Protective Zoning By-law (May 2025 edition), p. 38
    Any person, firm or corporation violating any section or provision of this Bylaw shall be fined one hundred (100) dollars for each offense. Each day that such offense continues shall constitute a separate offense.
  7. Sec. 4115 By-Right Accessory Apartment, Protective Zoning By-law (May 2025 edition), p. 36
    An accessory apartment (non-rental) is allowed as an accessory use to an owner occupied single-family dwelling in residential zoning districts in accordance with the following requirements.
  8. Sec. 4115(a), Protective Zoning By-law (May 2025 edition), p. 36
    The accessory apartment shall contain a maximum floor area of 800 square feet and shall not contain more than one bedroom.
  9. May 5, 2025 ATM, Article 17 (Sec. 4130 rewrite) vote, 2025 Town Meeting Results (Jan 13, 2025 STM; May 5, 2025 ATM; Nov 17, 2025 STM) - certified votes and article text, p. 21
    This was a counted vote and declared carried by the Moderator. The vote was 318 yeas and 57 nays.
  10. Nov 17, 2025 STM, Article 4 (Expanded ADU) vote, 2025 Town Meeting Results (Jan 13, 2025 STM; May 5, 2025 ATM; Nov 17, 2025 STM) - certified votes and article text, p. 34
    This was a counted vote and declared not carried by the Moderator by the required two-thirds majority. The vote was 100 yeas and 76 nays.
  11. Historic District Committee, Board Overview, Old King's Highway Historic District Committee (Sandwich) page
    The Old King's Highway Historic District includes all properties within the area north of the centerline of Route 6 to the Cape Cod Bay low water line, extending from the Town of Bourne to the border with the Town of Barnstable.
This page summarizes Sandwich's posted bylaws as of 2026-10-20. Bylaws are amended, and individual lots can have overlays, subdivision covenants, or HOA rules that are stricter. Confirm with Building Department (Building Commissioner administers and enforces the Protective Zoning By-law, incl. s.4130 ADUs, and the general bylaw Ch. 12 Short-Term Rentals; zoning complaints on the Zoning Complaint Form), Town Hall Annex, 100 Route 6A, Sandwich MA 02563; email building@sandwichmass.org; setback questions setbacks@sandwichmass.org (508-888-4200) before you build. Spot an error?