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Can I build an ADU in Bourne, Massachusetts?

Bourne, Barnstable County · Bylaws checked 2026-10-20 · Reviewed · 17 cited sections

Allowed with a permit

Yes. Bourne allows one accessory dwelling unit by right on a residential lot, up to 1,500 sq ft or half the main home's floor area, whichever is smaller. The posted bylaw still lists owner-occupancy, a 5,000 sq ft minimum lot and a 2-bedroom cap; Town Meeting voted on May 4, 2026 to remove them (Attorney General approval not confirmed), and the Planning Board says the town already permits ADUs that way. Short-term rental of the ADU or the main house is not allowed, and the ADU can't be rented for less than 90 days.

How allowedOne ADU by right per lot (building permit) [1]
Districts (use table)Yes in R-40, R-80, V-B, B-1, B-2 and B-4; No in B-3 and GD [17]
Max size1,500 sq ft or 1/2 of the main home's gross floor area, whichever is smaller [11]
Short-term rentalNot allowed for the ADU or the main house [5]
Minimum rental period90 days, no weekly or daily rentals (2026 text applies it to the ADU; posted text to both units) [13]
Owner occupancyIn posted bylaw; removed by May 4, 2026 Town Meeting vote (AG approval not confirmed) [8]
5,000 sq ft minimum lotIn posted bylaw; removed by May 4, 2026 Town Meeting vote (AG approval not confirmed) [7]
2-bedroom capIn posted bylaw; removed by May 4, 2026 Town Meeting vote (AG approval not confirmed) [8]
Parking (2026 amendment)At least 1 space; none if within 0.5 mile of a commuter rail, subway, ferry or bus station [10]
Town Meeting voteArticle 28 passed by voice vote, May 4, 2026 [14]

Which rules apply now

Bourne's posted zoning bylaw (amended through October 20, 2025) still shows the older ADU rules. On May 4, 2026, Town Meeting passed Article 28 by voice vote [14], which rewrites them. We could not confirm Attorney General approval, which a zoning change needs, and the posted bylaw hasn't been updated. The Planning Board says the changes are already being used in practice because state law supersedes the bylaw [15]. Ask the Building Department which text it will apply to your project.

Where ADUs are allowed

The use table lists an accessory dwelling as allowed ("Yes") in the R-40/R-80, V-B/B-1 and B-2/B-4 columns and "No" in B-3 and GD [17]. One ADU per lot is allowed by right, administered by the Building Commissioner [1]. Article 28 also allows ADUs in the Downtown Neighborhood District [9].

Old rules Article 28 removes

The posted text requires a 5,000 sq ft minimum lot [2], caps the unit at two bedrooms [3], and requires the owner to live in the main home or the ADU [4]. Article 28 removes the minimum lot [7] and the bedroom and owner-occupancy rules [8]. State law separately bars owner-occupancy and minimum-lot rules for a protected ADU of up to 900 sq ft.

Size

The limit is 1,500 sq ft or half the main home's gross floor area, whichever is smaller [11]. Bourne is keeping 1,500 sq ft, above the state's 900 sq ft protected size [12]. A unit of 901 to 1,500 sq ft is outside state protection, so only the local bylaw covers it; until Attorney General approval is confirmed, ask whether the posted owner-occupancy, lot and bedroom rules still apply to it. Under Article 28, a unit larger than 50% of the main home needs a supportive finding from the Zoning Board of Appeals [16]. Lot coverage limits still apply.

Rentals

The posted bylaw says neither the ADU nor the main house may be used for short-term rental, summer rental, boarding and lodging, or other commercial use (a home occupation is allowed) [5], and both must be rented for at least 90 days at a time [6]. Article 28 keeps the short-term rental ban for both units but strikes the words "summer rental", and its 90-day minimum [13] names only the ADU. The two units must stay in common ownership. State law lets towns restrict short-term rentals of ADUs, but state law may override the 90-day minimum for longer rentals.

Parking

Article 28 requires at least 1 space per ADU, or none within 0.5 mile of a commuter rail, subway, ferry or bus station [10]. Septic or sewer capacity must be adequate.

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

Next steps

  1. Ask the Building & Inspection Department (Town Hall Room 203, 508-759-0600 ext. 1512) which version of §4120 they will apply to your project, since the May 2026 amendment isn't in the posted bylaw yet.
  2. Check your zoning district (ADUs are listed as allowed in R-40, R-80, V-B, B-1, B-2 and B-4) and work out your size limit: 1,500 sq ft or half the main home's gross floor area, whichever is smaller.
  3. Have your septic capacity (or sewer connection) checked, prepare a certified plot plan showing the ADU, parking, setbacks and lot coverage, and apply for a building permit through the town's OpenGov portal.
  4. If the lot is near wetlands or the water, check with the Conservation Commission before you file.

Common questions

Can I build an ADU in Bourne, Massachusetts?
Yes. Bourne allows one accessory dwelling unit by right per lot with a building permit; the use table lists ADUs as allowed in R-40, R-80, V-B, B-1, B-2 and B-4, but not in B-3 or GD. Article 28, passed at the May 4, 2026 Town Meeting, also allows ADUs in the Downtown Neighborhood District.
Does Bourne, MA still require the owner to live on the property to have an ADU?
It depends on which text applies. The posted bylaw still requires owner-occupancy, a 5,000 sq ft minimum lot and a 2-bedroom cap. Town Meeting voted on May 4, 2026 to remove them, but Attorney General approval isn't confirmed. The Planning Board says the town already permits ADUs that way. State law bars owner-occupancy rules for protected ADUs up to 900 sq ft.
How big can an ADU be in Bourne, Massachusetts?
Up to 1,500 sq ft or half the main home's gross floor area, whichever is smaller. A unit of 901 to 1,500 sq ft is larger than the state's 900 sq ft protected size, so only the local bylaw covers it; ask the Building Department which version of §4120 applies to it.
Can I rent my ADU as an Airbnb in Bourne, Massachusetts?
No. Short-term rental of the ADU or the main house isn't allowed, and the ADU can't be rented for less than 90 days, with no weekly or daily rentals. The posted bylaw applies the 90-day minimum to both units; the 2026 amendment names only the ADU. State law may override the 90-day minimum for longer rentals.
How much parking does an ADU need in Bourne, MA?
Under the May 2026 amendment, at least 1 space per ADU, or none if the lot is within 0.5 mile of a commuter rail, subway, ferry or bus station. Attorney General approval of the amendment isn't confirmed, so ask the Building Department which rules it applies.

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

  1. §4120 Accessory Dwelling; §4121(a), Town of Bourne Zoning Bylaw ('2025 Zoning Bylaw', as most recently amended at the Special Town Meeting October 20, 2025), p. 155
    The Building Commissioner/Chief Zoning Enforcement Officer shall administer and enforce the provisions of this section. An accessory dwelling may be granted only if consistent with the following: 4121. Development Requirements. a) One accessory dwelling is permitted as a by right use to a lawful single- family use on the same lot.
  2. §4121(d) (pre-2026 text), Town of Bourne Zoning Bylaw ('2025 Zoning Bylaw', as most recently amended at the Special Town Meeting October 20, 2025), p. 155
    d) Minimum lot size is 5,000 square feet. Less than 5,000 square feet requires conformance with section 2450.
  3. §4121(e) (pre-2026 text), Town of Bourne Zoning Bylaw ('2025 Zoning Bylaw', as most recently amended at the Special Town Meeting October 20, 2025), p. 155
    e) The maximum size of an accessory dwelling is 1,500 square feet and contains no more than two bedrooms.
  4. §4122(a) (pre-2026 text), Town of Bourne Zoning Bylaw ('2025 Zoning Bylaw', as most recently amended at the Special Town Meeting October 20, 2025), p. 156
    a) Either the principal or the accessory unit must be owner-occupied. Fractional ownership is prohibited.
  5. §4122(b), Town of Bourne Zoning Bylaw ('2025 Zoning Bylaw', as most recently amended at the Special Town Meeting October 20, 2025), p. 156
    b) An accessory dwelling and primary dwelling authorized under these provisions shall not be used for short-term rental, summer rental, boarding and lodging, or other commercial use except for a home occupation according to Section 4110.
  6. §4122(c), Town of Bourne Zoning Bylaw ('2025 Zoning Bylaw', as most recently amended at the Special Town Meeting October 20, 2025), p. 156
    c) The ADU and primary dwelling may not be rented for periods shorter than 90 days at a time and are prohibited from any use as rental units on a weekly or daily basis.
  7. May 4, 2026 ATM Article 28, Explanation item 3, Annual Town Meeting May 4, 2026 - Voter Handbook (Article 28: Zoning Bylaw Amendment - Accessory Dwelling Units; Article 29 downtown front setbacks), p. 60
    3. Remove Lot Size requirements under section 4120(d), which currently requires a minimum lot size of 5,000 square feet.
  8. May 4, 2026 ATM Article 28, Explanation items 5-6, Annual Town Meeting May 4, 2026 - Voter Handbook (Article 28: Zoning Bylaw Amendment - Accessory Dwelling Units; Article 29 downtown front setbacks), p. 60
    5. Removing the requirement for number of bedrooms in an ADU. 6. Removing requirements for owner occupancy in section 4122(a).
  9. May 4, 2026 ATM Article 28, Explanation item 1, Annual Town Meeting May 4, 2026 - Voter Handbook (Article 28: Zoning Bylaw Amendment - Accessory Dwelling Units; Article 29 downtown front setbacks), p. 60
    1. Allowing Accessory Dwelling Units in the Downtown Neighborhood District of our Downtown District.
  10. Article 28, §3320 Table of Requirements (as amended), Annual Town Meeting May 4, 2026 - Voter Handbook (Article 28: Zoning Bylaw Amendment - Accessory Dwelling Units; Article 29 downtown front setbacks), p. 55
    Accessory Dwelling Units Minimum of 1 space per Accessory Dwelling Unit; no parking space required for Accessory Dwelling Units located not more than 0.5 miles from a commuter rail station, subway station, ferry terminal or bus station.
  11. Article 28, Section V Definitions - Accessory Dwelling Unit (as amended), Annual Town Meeting May 4, 2026 - Voter Handbook (Article 28: Zoning Bylaw Amendment - Accessory Dwelling Units; Article 29 downtown front setbacks), p. 59
    b) is not larger in Gross Floor Area than ½ the Gross Floor Area of the Principal Dwelling or 1500 square feet, whichever is smaller.
  12. May 4, 2026 ATM Article 28, Explanation, Annual Town Meeting May 4, 2026 - Voter Handbook (Article 28: Zoning Bylaw Amendment - Accessory Dwelling Units; Article 29 downtown front setbacks), p. 60
    The maximum size of ADUs built in the Town of Bourne is to remain at 1500 square feet with these zoning bylaw changes.
  13. Article 28, §4122(b) as amended (the words 'and primary dwelling' after 'The ADU' are struck through, so the 90-day rule names only the ADU), Annual Town Meeting May 4, 2026 - Voter Handbook (Article 28: Zoning Bylaw Amendment - Accessory Dwelling Units; Article 29 downtown front setbacks), p. 57
    may not be rented for periods shorter than 90 days at a time and are prohibited from any use as rental units on a weekly or daily basis.
  14. May 4, 2026 ATM transcript, Article 28 vote, Annual Town Meeting May 4, 2026 - Town Meeting Transcript (vote record for Article 28 ADU amendment), p. 168
    MODERATOR AMY KULLAR: I did hear a couple NOS, but I declare that the motion of the Planning Board has passed. (Article 28 passed.)
  15. May 4, 2026 ATM Article 28, Explanation, Annual Town Meeting May 4, 2026 - Voter Handbook (Article 28: Zoning Bylaw Amendment - Accessory Dwelling Units; Article 29 downtown front setbacks), p. 60
    These changes are already being used in practice while permitting Accessory Dwelling Units as Massachusetts General Law supersedes the Zoning Bylaw.
  16. Article 28, §4121(e) (as amended), Annual Town Meeting May 4, 2026 - Voter Handbook (Article 28: Zoning Bylaw Amendment - Accessory Dwelling Units; Article 29 downtown front setbacks), p. 56
    Any Accessory Dwelling Units proposed larger than 50% of the primary dwelling require a supportive finding from the Zoning Board of Appeals.
  17. §2220 Use Regulation Schedule, Accessory Uses (table header and row), Town of Bourne Zoning Bylaw ('2025 Zoning Bylaw', as most recently amended at the Special Town Meeting October 20, 2025), p. 32
    DISTRICT R-40 R-80 V-B B-1 B-2 B-4 B-3 GD ACCESSORY USES Accessory dwelling (See Section 4120) Yes Yes Yes No No
This page summarizes Bourne'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 & Inspection Department (also the Zoning Enforcement Office; Building Commissioner/Chief Zoning Enforcement Officer), Bourne Town Hall Room 203, 24 Perry Avenue, Buzzards Bay MA 02532; complaints via the OpenGov portal; Conservation office 508-759-0600 ext. 1344; Health Department via https://www.bourne-ma.gov/1928/Health-Department (508-759-0600 ext. 1512) before you build. Spot an error?