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Accessory Dwelling Units (ADUs) in Massachusetts: rules in 22 towns compared
Can I build an ADU (in-law apartment, guest house, garage apartment)? Here's how each town answers it. Click a town for the details and the exact bylaw text.
Last reviewed
This page is for Massachusetts homeowners thinking about an in-law apartment, a garage apartment or a backyard cottage. Since February 2, 2025, the Affordable Homes Act (M.G.L. c. 40A, §3) has protected one accessory dwelling unit (ADU) per lot in any zoning district that allows single-family homes. Your town can't ban it, require a special permit for it, require you to live on the property, or require more than one extra parking space (none near transit). A protected ADU can be attached or detached and can be no larger than 900 sq ft or half the main home's floor area, whichever is smaller. Towns can still apply reasonable site plan review, setbacks and Title 5 septic rules, and they can restrict or ban short-term rentals of ADUs.
All 22 towns we cover for this topic allow an ADU. Most, including Belmont, Concord, Hamilton, Hingham, Swampscott, Wayland and Weston, approve one with a building permit, while Carlisle, Dover, Falmouth and Scituate send it through Planning Board site plan review. Most of these towns don't allow the ADU to be used as a short-term rental. Cohasset, Hamilton, Manchester-by-the-Sea and Scituate offer a larger ADU by special permit. Some bylaws still carry older rules that state law may override, such as owner-occupancy requirements in Lexington and Needham and a special permit for detached ADUs in Chatham. Pick your town below for the details and the bylaw text.
Town-by-town comparison
| Town | Verdict | Short answer |
|---|---|---|
| Wellesley | Allowed with a permit | Yes. Wellesley's Zoning Bylaw allows one accessory dwelling unit (attached or detached) with any single-family home in a Single Residence District, with a building permit and Planning Department compliance certification. The ADU must be 250 to 900 sq ft and no more than half the main home's floor area, and it can't be rented for less than 30 days. |
| Weston | Allowed with a permit | Yes. One accessory dwelling unit (ADU) is allowed by right in Weston's Single Family Residence Districts with a building permit from the Building Inspector. It can be no larger than half the main home's floor area or 900 sq ft, whichever is smaller. A detached ADU must sit in the rear yard, and it can't be used as a short-term rental. If you can't meet the by-right conditions, you need Planning Board site plan approval. |
| Lexington | Allowed | Yes. In Lexington's single-family districts (RO and RS) a basic accessory apartment inside your house is allowed by right if it's no more than 1,000 sq ft with up to two bedrooms; a larger apartment in the house or one in a detached accessory structure needs a special permit from the Board of Appeals. The bylaw we reviewed also requires the owner to live on the property, a rule state law may now override. |
| Concord | Allowed with a permit | Yes. Concord allows one accessory dwelling unit per lot, attached or in a detached accessory building, with a building permit from the Building Commissioner. It can be up to 1,000 sq ft, needs one parking space (none near transit), and must meet the main house's setbacks; there's no owner-occupancy rule. |
| Needham | Allowed with a permit | Under Needham's Zoning By-Law (version amended to May 2025; rules may have changed since), one accessory dwelling unit is allowed inside a single-family detached house with a building permit from the Building Commissioner. It's capped at 900 sq ft of living space and one bedroom, and the bylaw still requires one of the two units to be owner-occupied and bars ADUs in accessory buildings, rules that Massachusetts' ADU law (in effect since Feb 2, 2025) may override. |
| Dover | Allowed with board review | Yes. Dover allows one attached or detached ADU with a home in its R, R-1, R-2, B, M, M-P and R-M districts after Partial Site Plan Review by the Planning Board, under § 185-43 as amended at the May 4, 2026 Town Meeting. The ADU can be no larger than 50% of the main home's gross floor area (basements count) or 900 square feet, whichever is less, and it can't be used as a short-term rental. |
| Sudbury | Allowed with a permit | Yes. Sudbury's 2025 Section 5500 (adopted at the May 5, 2025 Town Meeting and partly approved by the Attorney General) allows one ADU per lot as of right in Single Residence Districts A and C with a building permit. It can be attached or detached, must be no larger than 900 sq ft or 50% of the main house's floor area (whichever is smaller), needs one off-street parking space (none near transit), and can't be used as a short-term rental. |
| Wayland | Allowed with a permit | Yes. Under the zoning amendment adopted in April 2025, one accessory dwelling unit per lot is allowed by right in the Single Residence District with a building permit. It can be no larger than half the main house's gross floor area or 900 sq ft, whichever is less, and it needs Board of Health septic approval and one off-street parking space. |
| Lincoln | Allowed with a permit | Yes. Lincoln's zoning bylaw grants a building permit for one attached or detached ADU per lot in any single-family district, up to 900 sq ft or half the main house's floor area, whichever is smaller. A detached ADU also needs Planning Board site plan review. A larger "accessory apartment" of up to 1,200 sq ft is also possible, but it comes with an owner-occupancy rule and a 40,000 sq ft minimum lot. |
| Belmont | Allowed | Yes. Belmont's Zoning By-Law allows one accessory dwelling unit by right as an accessory use in the Single Residence and General Residence districts, attached or detached. It can be no larger than half the main home's gross floor area or 900 sq ft, whichever is smaller, and needs one extra parking space unless your lot is within 0.5 miles of a transit station. |
| Winchester | Allowed with board review | Yes. Winchester's November 2024 ADU amendment (partly approved by the Attorney General in June 2025) allows one ADU by right on a lot with a home, attached or in a detached accessory building, up to 900 sq ft or half the main home's floor area, whichever is less. ADUs go through site plan review, need one off-street parking space unless within a half mile of a commuter rail or bus station, and can't be used as short-term rentals. |
| Hingham | Allowed with a permit | Yes. Hingham's Zoning By-Law allows one accessory dwelling unit per lot by right in Residence A, B, C and E, with a building permit. It can be no bigger than half the main home's floor area or 900 sq ft, whichever is smaller, needs one extra parking space, and can't be used as a short-term rental. |
| Cohasset | Allowed with a permit | Under the December 2024 zoning amendment, Cohasset allows one ADU per lot by right. It can be no bigger than 900 sq ft or half the main home's floor area, whichever is smaller, needs one extra off-street parking space (none near transit), and can't be used as a short-term rental. A larger ADU of up to 1,250 sq ft needs a special permit from the Zoning Board of Appeals, and the owner must live on the property. |
| Duxbury | 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. |
| Manchester-by-the-Sea | Allowed | Yes. Manchester-by-the-Sea's Zoning By-law allows one Standard ADU per lot by right in the residence districts, up to 900 sq ft or half the main home's floor area, whichever is smaller. A bigger 'Large' ADU (up to 1,200 sq ft) needs a special permit from the Zoning Board of Appeals. |
| Chatham | Allowed with a permit | Yes. Chatham's zoning bylaw allows one ADU per lot (up to 900 sq ft and 2 bedrooms), by right with a building permit if it's inside or attached to the house. The bylaw requires a ZBA special permit for a detached ADU, caps permits at 10 a year and requires a 12-month lease; state law likely overrides the special permit and the caps. |
| Falmouth | Allowed with board review | Yes. Since November 2024, Falmouth's zoning bylaw allows one accessory dwelling unit per lot as of right, up to 900 sq ft or half the main home's floor area, whichever is less. You need Planning Board Site Plan Review before a building permit, one on-site parking space, and the ADU can't be used for weekly or monthly summer rentals. |
| Barnstable | Allowed with a permit | Under the 2021 version of Barnstable's zoning ordinance we reviewed, one ADU per lot is allowed with a building permit from the Building Commissioner, either inside the house or in a detached accessory building. It can be no larger than 900 sq ft or half the main home's habitable floor area, whichever is smaller, with up to 2 bedrooms. The ordinance also requires that the ADU be used as a year-round rental (12-month minimum), but state law may override that. |
| Scituate | Allowed with board review | Yes. Scituate allows one accessory dwelling unit per lot through Planning Board Site Plan Review if it is no larger than half the main home's floor area or 900 sq ft, whichever is smaller. It can be inside the house, attached, or detached; it needs one off-street parking space (none within 0.5 miles of a commuter rail station, ferry terminal or bus station) and can't be rented for stays of 31 days or less. |
| Swampscott | Allowed with a permit | Yes. Swampscott's zoning bylaw allows one accessory dwelling unit (ADU) per lot by right in all four residence districts (A-1 to A-4), with just a building permit from the Building Commissioner. The ADU can be no larger than half the main home's floor area or 900 sq ft, whichever is smaller, and it can't be rented for less than 30 consecutive days. |
| Hamilton | Allowed with a permit | Yes. Hamilton allows one attached or detached ADU by right in all single-family residential districts with a building permit from the Building Commissioner. It can be no larger than 50% of the main home's gross floor area or 900 square feet, whichever is smaller, needs one off-street parking space, and can't be used as a short-term rental. |
| Carlisle | Allowed with board review | Yes. Carlisle allows one ADU per single-family lot, attached or detached, up to 900 sq ft or half the main home's floor area, whichever is smaller. You need Site Plan Review by the Planning Board (with a public hearing) before you can apply for a building permit, and neither unit has to be owner-occupied. |
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.
Common questions about adu rules in Massachusetts
- What is the new ADU law in Massachusetts?
- Since February 2, 2025, the Affordable Homes Act (M.G.L. c. 40A, §3) has protected one ADU per lot in any district that allows single-family homes. Towns can't ban it, require a special permit, or unreasonably restrict building or renting it. State regulations at 760 CMR 71.00 explain which local rules count as unreasonable.
- Can I build an ADU on my property in Massachusetts?
- Usually yes, if your lot is in a district that allows single-family homes. One ADU of up to 900 sq ft or half the main home's floor area, whichever is smaller, is protected. Your town can still apply reasonable setback, height, site plan review and Title 5 septic rules, so the approval path varies by town.
- Is an ADU allowed by right in Massachusetts?
- Yes, for one protected ADU per lot: towns can't require a special permit or other discretionary approval for it. A second ADU on the same lot needs a special permit. Some towns also offer a larger ADU by special permit, and some still route ADUs through site plan review.
- Do I have to live on the property to have an ADU in Massachusetts?
- No. State law bars towns from requiring the owner to live in the main home or the ADU. A few bylaws we reviewed still contain owner-occupancy rules, and state law may override them for a protected ADU. Some towns keep an owner-occupancy rule only for a larger ADU approved by special permit.
- Do I need extra parking for an ADU in Massachusetts?
- It depends on where you live. A town can require no more than 1 extra parking space, and none at all if the lot is within 0.5 miles of a subway, commuter rail, ferry or bus station.
- Can I rent my ADU on Airbnb in Massachusetts?
- It depends on your town. State law lets towns restrict or ban short-term rentals of ADUs, and most towns we cover don't allow an ADU to be used as a short-term rental. Long-term renting can't be unreasonably restricted.
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