Can I build an ADU in Swampscott, Massachusetts?
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.
| Where allowed | By right (Y) in A-1, A-2, A-3, A-4, B-1 and B-2; not allowed (N) in B-3, B-4 or I [1] |
| Max size | 1/2 of the main dwelling's gross floor area or 900 sq ft, whichever is smaller [2] |
| Number per lot | 1 [3] |
| Extra parking | 1 off-street space, none if within 1/2 mile of a transit station [4] |
| Minimum rental period | 30 consecutive days [5] |
| Approval | Building permit from the Building Commissioner (site plan, floor plans, elevations) [6] |
These rules come from the zoning bylaw version updated through the May 19, 2025 Town Meeting and may have changed since.
Where ADUs are allowed
The Table of Principal Uses lists "Accessory Dwelling Unit (See §5.11.0.0.)" as allowed by right (Y) in the A-1, A-2, A-3 and A-4 residence districts and in the B-1 and B-2 business districts; it is not allowed in B-3, B-4 or the I district [1].
What counts as an ADU
An ADU is a self-contained unit with its own sleeping, cooking and sanitary facilities on the same lot as the main home. It needs a separate entrance (from outside or through a shared hall) that meets the building code, and it can be no larger than half the main home's gross floor area or 900 square feet, whichever is smaller [2]. The bylaw doesn't limit you to attached or detached; normal setback, height and parking rules still apply. Where the bylaw's definition conflicts with the state ADU regulations (760 CMR 71.00), the state rules control [7].
Design and use rules
- Only one ADU per lot [3].
- If the house has more than one front entrance, one must look like the main entrance, and exterior stairs to an upper-floor ADU must be on the side or rear.
- The ADU may not have its own separate utilities (water, sewer, electricity) [8].
- One extra off-street parking space is required unless the lot is within ½ mile of a transit station [4].
- No renting the ADU for less than 30 consecutive days, so it can't be used as a short-term rental [5].
Nonconforming lots
If the lot, house or existing accessory building is nonconforming, the Zoning Board of Appeals may need to find (by majority vote) that the change is not substantially more detrimental to the neighborhood before a building permit issues; no special permit is required.
State law
The bylaw has no owner-occupancy requirement and allows ADUs by right, consistent with Massachusetts' ADU law. The ban on separate utilities may be tested against the state's "unreasonable restriction" standard. Proposed December 2026 zoning changes to ADU application rules had not been adopted when this copy was posted.
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Next steps
- Confirm your zoning district on the Swampscott zoning map and check whether the lot or house is nonconforming.
- Prepare a site plan, interior floor plans and building elevations showing the ADU's size (no more than half the house's floor area or 900 sq ft).
- Apply for a building permit with the Building Department (Building Commissioner, Town Hall, 22 Monument Ave., 781-596-8857).
- If you're in a local historic district, get a Certificate of Appropriateness or Non-Applicability from the Historic District Commission first.
Common questions
- Can I build an ADU in Swampscott, Massachusetts?
- Yes. The zoning bylaw allows one accessory dwelling unit per lot by right in the A-1 to A-4 residence districts, with a building permit from the Building Commissioner.
- How big can an ADU be in Swampscott, Massachusetts?
- No larger than half the main home's floor area or 900 sq ft, whichever is smaller.
- Does an ADU need parking in Swampscott, Massachusetts?
- It needs 1 off-street space, with none required if within 1/2 mile of a transit station.
- Can I rent my ADU short term in Swampscott, Massachusetts?
- No. An ADU can't be rented for less than 30 consecutive days.
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. 2.2.3.0 Table of Principal Uses, A.5, Zoning By-Law (Version 5-21-25; updated through Annual Town Meeting May 19, 2025), p. 8
5. Accessory Dwelling Unit (See §5.11.0.0.) Y Y Y Y Y Y N N N A
- Sec. 5.11.1.1, Zoning By-Law (Version 5-21-25; updated through Annual Town Meeting May 19, 2025), p. 133
5.11.1.1. Accessory Dwelling Unit or ADU: a self-contained housing unit, inclusive of sleeping, cooking and sanitary facilities located on the same lot as a principal dwelling, subject to otherwise applicable dimensional and parking requirements, that: (i) maintains separate entrances, either directly from the outside or through an entry hall or corridor shared with the principal dwelling, sufficient to meet the requirements of the state building code for safe egress and (ii) 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.
- Sec. 5.11.3.1, Zoning By-Law (Version 5-21-25; updated through Annual Town Meeting May 19, 2025), p. 134
5.11.3.1. Only one (1) ADU may be located on a Lot.
- Sec. 5.11.3.5, Zoning By-Law (Version 5-21-25; updated through Annual Town Meeting May 19, 2025), p. 134
In addition to the minimum parking requirement for the principal dwelling, one (1) dedicated off- street parking space is required for an ADU located on a lot that is not located within ½ mile of a transit station.
- Sec. 5.11.3.6, Zoning By-Law (Version 5-21-25; updated through Annual Town Meeting May 19, 2025), p. 134
5.11.3.6. No ADU shall be offered for rent for a period of less than thirty (30) consecutive days.
- Sec. 5.11.4.0, Zoning By-Law (Version 5-21-25; updated through Annual Town Meeting May 19, 2025), p. 134
5.11.4.0. Application Requirements Prior to a building permit being issued for an ADU, the applicant shall provide the following to the Building Commissioner:
- Sec. 5.11.2.0, Zoning By-Law (Version 5-21-25; updated through Annual Town Meeting May 19, 2025), p. 134
conflict between the definition contained in Article VI of this Bylaw and 760 CMR 71.00, the latter shall control.
- Sec. 5.11.3.3, Zoning By-Law (Version 5-21-25; updated through Annual Town Meeting May 19, 2025), p. 134
5.11.3.3. The ADU shall not have separate or independent utilities, such as water, sewer and electricity, from the dwelling unit.