Can I build an ADU in Winchester, Massachusetts?
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.
| Where allowed | By right in all districts on a lot where a single-family dwelling exists or is allowed (state law also protects ADUs on duplex lots) [1] |
| Number per lot | One ADU (an additional ADU only by special permit) [2] |
| Max size | 900 sq ft or half the principal dwelling's gross floor area, whichever is less [3] |
| Attached or detached | Either: within the home or in a detached accessory structure [7] |
| Parking | One off-street space; none within 1/2 mile of a commuter rail or bus station [4] |
| New garage for an ADU | Requires a special permit (may conflict with state law) [4] |
| Short-term rental | Not allowed (short-term rentals as defined in G.L. c. 64G) [5] |
| Review | Site plan review under Section 9.5 [6] |
Rules below come from the November 7, 2024 Town Meeting vote (Article 8) and the Attorney General's June 4, 2025 decision; we could not read the current codified bylaw on eCode360, so confirm Section 3.2.2 with the Building Department.
What the bylaw allows
Article 8 rewrote Section 3.2.2 so ADUs may be built as of right on a lot where a single-family dwelling exists or is allowed [1]. Only one ADU is allowed per lot unless a special permit allows another [2]. The definition covers a unit inside the house or in a detached accessory structure, with its own sleeping, cooking and sanitary facilities [7]. The voted redline strikes the old owner-occupancy requirement, the age-62/disability purpose language and the old two-bedroom limit.
Size, design and parking
An ADU can be no larger than half the main home's gross floor area or 900 sq ft, whichever is less [3]. It must be compatible with the primary residence, and the Zoning Enforcement Officer may consult the Design Review Committee; any new entrance should appear secondary to the main entrance. One off-street space is required, except within a half mile of a commuter rail or bus station; a new garage built for an ADU needs a special permit [4].
Review and rentals
All ADUs are subject to site plan review under Section 9.5 [6]. ADUs may not be used as short-term rentals or rented for less than 31 days [5]. The Attorney General approved the short-term-rental ban only as it tracks the state definition in G.L. c. 64G, and said site plan review must be clear and objective.
Attorney General decision
The Attorney General approved Article 8 only in part on June 4, 2025 [8], striking the special-permit requirement for ADUs on duplex lots and the special-permit language for ADUs added to nonconforming homes. The decision also says the Town cannot apply its minimum lot area requirement to ADUs [9].
State law
Massachusetts law since Feb 2, 2025 protects one ADU per lot by right and bars owner-occupancy, minimum lot size and similar limits. The special permit for a new ADU garage may also be open to challenge under the state ADU rules, so state law may override it.
See how Winchester compares with 8+ other Massachusetts towns on accessory dwelling units (adus) →
Next steps
- Ask the Building Department for the current codified Section 3.2.2 and the ADU application/site plan review checklist.
- Prepare a plan showing the ADU's gross floor area (max 900 sq ft or half the main home), entrance, setbacks and the off-street parking space.
- Submit for site plan review under Section 9.5 and apply for a building permit.
Common questions
- Can I build an ADU in Winchester, Massachusetts?
- Yes. One ADU is allowed by right on a lot with a home, attached or in a detached accessory building, through site plan review under Section 9.5. An additional ADU needs a special permit.
- How big can an ADU be in Winchester, Massachusetts?
- Up to 900 sq ft or half the main home's floor area, whichever is less.
- Does an ADU need parking in Winchester, Massachusetts?
- One off-street space is needed, but none within 1/2 mile of a commuter rail or bus station.
- Can I rent my ADU on Airbnb in Winchester, Massachusetts?
- No. ADUs can't be used as short-term rentals as defined in G.L. c. 64G.
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.
What the bylaw says
- Sec. 3.2.2 (Purpose) as amended by 2024 FTM Art. 8, quoted in AG Decision Sec. I, Attorney General decision (June 4, 2025) on Nov 2024 FTM Articles 7 and 8 (partial approval of ADU bylaw), p. 2
In all districts, ADUs may be constructed or established as a matter of right on a lot where a single family dwelling exists or is allowed
- Sec. 3.2.2(1), Fall Town Meeting Nov 7, 2024 Article 8 - ADU amendment (Sec. 3.2.2 and Sec. 10 definitions), p. 1
There shall be no more than one accessory unit ADU per single family or duplex lot, unless an additional ADU is allowed by a special permit.
- Sec. 3.2.2(3), Fall Town Meeting Nov 7, 2024 Article 8 - ADU amendment (Sec. 3.2.2 and Sec. 10 definitions), p. 2
An ADU may be no larger in gross floor area than one half of the gross floor area of the principal Dwelling Unit on the property or 900 square feet, whichever is less.
- Sec. 3.2.2(7), Fall Town Meeting Nov 7, 2024 Article 8 - ADU amendment (Sec. 3.2.2 and Sec. 10 definitions), p. 2
off-street parking space must be supplied for all ADUs except for ADUs within one-half mile of a commuter rail station or bus station. Parking may be in a driveway or a garage. Construction of a new garage for an ADU shall require a special permit.
- Sec. 3.2.2(9), Fall Town Meeting Nov 7, 2024 Article 8 - ADU amendment (Sec. 3.2.2 and Sec. 10 definitions), p. 2
ADUs may not be used as Short-Term Rentals, as such term is defined in G.L. c. 64G, §1 or otherwise rented for a period shorter than thirty-one (31) days.
- Sec. 3.2.2(10), Fall Town Meeting Nov 7, 2024 Article 8 - ADU amendment (Sec. 3.2.2 and Sec. 10 definitions), p. 3
All ADUs are subject to Site Plan Review as defined by Section 9.5 of these bylaws.
- Sec. 10 Definitions, Accessory Dwelling Unit, Fall Town Meeting Nov 7, 2024 Article 8 - ADU amendment (Sec. 3.2.2 and Sec. 10 definitions), p. 3
A self-contained housing unit, inclusive of sleeping, cooking and sanitary facilities, incorporated within the same structure as a single-family or duplex dwelling or in a detached accessory structure
- AG Decision, Case # 11645, Article 8, Attorney General decision (June 4, 2025) on Nov 2024 FTM Articles 7 and 8 (partial approval of ADU bylaw), p. 1
We partially approve Article 8 because the approved text does not conflict with state law.
- AG Decision, Sec. V.B, Attorney General decision (June 4, 2025) on Nov 2024 FTM Articles 7 and 8 (partial approval of ADU bylaw), p. 9
Therefore, the Town cannot impose the Table’s minimum lot area requirement on an ADU.