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Can I build an ADU in Yarmouth, Massachusetts?

Yarmouth, Barnstable County · Bylaws checked 2026-10-15 · Reviewed · 13 cited sections

Allowed with board review

Yarmouth's current zoning bylaw (Section 407) allows one "accessory apartment" per lot by special permit from the Zoning Board of Appeals in the residential districts, capped at 800 sq ft (studio/1-bedroom) or 900 sq ft (2-bedroom) and no more than 50% of the main home, with owner-occupancy and minimum lot sizes. These rules predate the state ADU law in effect since February 2, 2025, which protects one ADU per lot by right and may override the special permit, owner-occupancy, lot-size and parking rules; a rewrite to match state law goes to the November 16, 2026 Special Town Meeting and is not yet adopted.

Approval under current bylawSpecial permit from the Zoning Board of Appeals ("BA" in the Use Table) [1]
Number per lot1 accessory apartment [2]
Minimum lot size (current bylaw)10,000 sq ft (studio/1-bedroom); 15,000 sq ft (2-bedroom) [3]
Max size, studio/1-bedroom800 sq ft or 50% of main home's habitable area, whichever is smaller [4]
Max size, 2-bedroom900 sq ft or 50% of main home's habitable area, whichever is smaller; minimum 350 sq ft [5]
Parking (current bylaw)2 off-street spaces for the main home plus 2 for the apartment [6]
Owner-occupancy (current bylaw)Owner must live in the main home or the apartment [7]
LeasesMinimum 12 consecutive months; no seasonal or short-term rentals [8]
Proposed (not yet adopted) max size900 sq ft or 50% of the main home's gross floor area, whichever is smaller [10]

What the current bylaw says

Yarmouth calls ADUs "accessory apartments." Under the Use Table they need a special permit from the Zoning Board of Appeals [1]. The Use Table lists them by special permit in the Residential (Res.) and RS-40 districts, the B1 and B2 districts, and the APD and MOD districts, and prohibits them elsewhere. Only one is allowed per lot [2]. It can be inside or attached to the house or in a detached accessory building, and it must look like part of a single-family property. The lot must be at least 10,000 sq ft for a studio or 1-bedroom unit and 15,000 sq ft for a 2-bedroom unit [3]. Units are capped at 2 bedrooms; studio/1-bedroom units at 800 sq ft and 2-bedroom units at 900 sq ft, in both cases no more than 50% of the main home's habitable area, and no unit may be under 350 sq ft [4][5].

The bylaw also requires 2 off-street spaces for the house plus 2 for the apartment [6], owner-occupancy of one of the two units [7], and year-round leases of at least 12 months with no short-term rentals [8]. Accessory apartments cannot be sold separately or made into condos [13], and they need a Certificate of Occupancy. Rented units must be registered each year with the Health Department.

State law may override parts of this

This Section 407 text was adopted in 2023, before the state Affordable Homes Act. Since February 2, 2025, state law protects one ADU per lot by right in districts that allow single-family homes, so state law may override the special permit, owner-occupancy, minimum lot size and 2-space parking requirements. The town's own summary of the pending rewrite says these provisions "are no longer enforceable" [9].

Rules are about to change (proposal, not yet adopted)

A proposed ADU zoning article goes to the November 16, 2026 Special Town Meeting. If passed and approved by the Attorney General, it would allow one ADU by right, cap it at 900 sq ft or 50% of the main home's gross floor area (minimum 350 sq ft) [10], require one parking space (none within 0.5 mile of a transit station) [12], and bar short-term rentals in the ADU and in the main house on the same lot [11]. Until then, the text above is what the bylaw says. Check with the Building Department after the vote.

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

Next steps

  1. Call the Building Department (508-398-2231 ext. 1261) to confirm whether it is processing ADUs under state law (by right) or still requiring a ZBA special permit, especially after the November 16, 2026 Special Town Meeting.
  2. Prepare a site plan (showing parking and landscaping) and floor plans; for additions or new construction, add elevation drawings with building materials.
  3. If the lot is north of Route 6 in the Old King's Highway Historic District, get OKH approval for exterior work.
  4. Get a building permit and, when finished, a Certificate of Occupancy; register the unit with the Health Department if you will rent it.

Common questions

Can I build an ADU in Yarmouth, Massachusetts?
It depends on how the rules settle. Yarmouth's current bylaw allows one accessory apartment per lot by Zoning Board of Appeals special permit, but state ADU law in effect since February 2, 2025 protects one ADU per lot by right and may override that. A rewrite goes to the November 16, 2026 Special Town Meeting and is not yet adopted, so confirm with the Building Department.
How big can an ADU be in Yarmouth, Massachusetts?
Under the current bylaw, a studio or 1-bedroom unit is capped at 800 sq ft and a 2-bedroom unit at 900 sq ft, each no more than 50% of the main home's habitable area and at least 350 sq ft. A proposal for the November 16, 2026 Special Town Meeting, not yet adopted, would cap ADUs at 900 sq ft or 50% of the main home's gross floor area.
Can I rent my ADU as an Airbnb in Yarmouth, Massachusetts?
No. The current bylaw requires accessory apartment leases of at least 12 consecutive months, with no seasonal or short-term rentals. A proposal for the November 16, 2026 Special Town Meeting, not yet adopted, would also bar short-term rentals in the ADU and in the main house on the same lot.
Do I have to live on the property to have an ADU in Yarmouth, Massachusetts?
Under the current bylaw, yes: the owner must live in the main home or the apartment, and the lot needs 2 off-street spaces for the house plus 2 for the apartment. But state law since February 2, 2025 may override the owner-occupancy and parking rules, and a rewrite before the November 16, 2026 Special Town Meeting is not yet adopted.

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

  1. Use Table 202.5, A10 Accessory apartments, Accessory Apartments zoning bylaw excerpt (Use Table A10 + Section 407; effective 11/7/23), p. 1
    Accessory Apartments require a Special Permit from the Zoning Board of Appeals (denoted as a “BA”) in the following zoning districts if they meet the criteria outlined in Section 407 of the Zoning Bylaw.
  2. §407.3(2), Town of Yarmouth Zoning Bylaw (amended through April 28, 2026), p. 86
    Only one accessory apartment per lot shall be allowed. No variance shall be permitted from this requirement.
  3. §407.3(3)(a), Town of Yarmouth Zoning Bylaw (amended through April 28, 2026), p. 86
    Minimum lot size shall be 10,000 square feet for studio or 1-bedroom accessory apartments. Minimum lot size shall be 15,000 square feet for 2-bedroom accessory apartments.
  4. §407.3(6), Town of Yarmouth Zoning Bylaw (amended through April 28, 2026), p. 87
    Studio and 1-bedroom accessory apartments shall have a maximum habitable floor area that is not larger than 50% of the habitable floor area of the principal single family dwelling unit, or 800 square feet, whichever is smaller.
  5. §407.3(6), Town of Yarmouth Zoning Bylaw (amended through April 28, 2026), p. 87
    Two-bedroom accessory apartments shall have a maximum habitable floor area that is not larger than 50% of the habitable floor area of the principal single family dwelling unit, or 900 square feet, whichever is smaller. Regardless of habitable floor area of the principal dwelling, accessory apartments shall not be less than 350 square feet.
  6. §407.3(7), Town of Yarmouth Zoning Bylaw (amended through April 28, 2026), p. 87
    At least two (2) off-street parking spaces on the premises shall be required for use by residents of the principal dwelling unit and two (2) additional off-street parking spaces shall be required for use by the residents of the accessory apartment.
  7. §407.3(11), Town of Yarmouth Zoning Bylaw (amended through April 28, 2026), p. 87
    The owners of the principal structure shall occupy, as their primary residence, either the principal dwelling unit or the accessory apartment.
  8. §407.3(12), Town of Yarmouth Zoning Bylaw (amended through April 28, 2026), p. 87
    All lease agreements shall be for a minimum of twelve (12) consecutive months with no seasonal or Short-Term Rentals and no subletting or room rentals.
  9. Summary, ADU Zoning Article 1 (proposed, Nov 16, 2026 STM), Zoning Amendments and General Bylaw for November 16, 2026 Special Town Meeting (STR General Bylaw Ch. 110, STR zoning/sunset articles, ADU article) - Planning Board articles and summary, p. 2
    Per 760 CMR 71.00, some provisions in our current zoning bylaw have been eliminated as they are no longer enforceable, such as requiring a Special Permit, owner occupancy, minimum lot size, 2 parking spaces per ADU, ineligibly properties, and any requirements for an ADU not also required for a single- family home.
  10. Proposed §407.4(4) (Zoning Article 1, Draft #3), Zoning Amendments and General Bylaw for November 16, 2026 Special Town Meeting (STR General Bylaw Ch. 110, STR zoning/sunset articles, ADU article) - Planning Board articles and summary, p. 12
    An ADU shall not be larger than 900 square feet or 50% of the Gross Floor Area (GFA) of the Principal Dwelling, whichever is smaller.
  11. Proposed §407.4(7)-(8) (Zoning Article 1, Draft #3), Zoning Amendments and General Bylaw for November 16, 2026 Special Town Meeting (STR General Bylaw Ch. 110, STR zoning/sunset articles, ADU article) - Planning Board articles and summary, p. 13
    Accessory Dwelling Units shall not be used for Short Term Rentals. 8. No Principal Dwelling on a lot with an ADU may be operated as a Short-Term Rental.
  12. Proposed §407.4(5) (Zoning Article 1, Draft #3), Zoning Amendments and General Bylaw for November 16, 2026 Special Town Meeting (STR General Bylaw Ch. 110, STR zoning/sunset articles, ADU article) - Planning Board articles and summary, p. 13
    In addition to parking required for other structures and uses on the property, ADUs shall have one designated on-site parking space on the property if the ADU is located outside the 0.5 mile radius of a Transit Station. No on-site parking is required for a Protected Use ADU located within a 0.5 radius of a Transit Station.
  13. §407.3(9), Town of Yarmouth Zoning Bylaw (amended through April 28, 2026), p. 87
    An accessory apartment is not intended for sale and shall not be held in separate ownership from the principal structure/dwelling unit nor placed in a condominium form of ownership.
This page summarizes Yarmouth's posted bylaws as of 2026-10-15. Bylaws are amended, and individual lots can have overlays, subdivision covenants, or HOA rules that are stricter. Confirm with Building Department (Inspectional Services) (508-398-2231 ext. 1261) before you build. Spot an error?