Can I build an ADU in Manchester-by-the-Sea, Massachusetts?
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.
| Standard ADU max size | 900 sq ft or half the main home's gross floor area, whichever is smaller [1] |
| Standard ADU approval | Allowed by right (Y) in Districts A, B, C, D1, D2, E and G [2] |
| Large ADU max size | 1,200 sq ft or half the main home's gross floor area, whichever is smaller [3] |
| Large ADU approval | Special permit from the Zoning Board of Appeals (Districts A, B, C, D1, D2, E) [2] |
| Parking (Standard ADU) | 1 off-street space, unless within 1/2 mile of the commuter rail station [4] |
| Number per lot | One Standard ADU; a Large ADU isn't allowed where another ADU already exists [5] |
| Short-term rentals | Not permitted in any ADU [6] |
| Large ADU minimum lease | 6 months [7] |
Two kinds of ADU
The bylaw defines a Standard ADU as a self-contained unit with its own sleeping, cooking and bathroom facilities, a separate entrance, and no more than half the main home's gross floor area or 900 sq ft, whichever is smaller [1]. A Large ADU is bigger than that but no more than half the main home's floor area or 1,200 sq ft [3].
Where they're allowed
In the use table, a Standard ADU is marked "Y" (by right) and a Large ADU "ZBA" (special permit from the Zoning Board of Appeals) [2]. Standard ADUs are allowed in Districts A, B, C, D1, D2, E and G; Large ADUs in A, B, C, D1, D2 and E, but not G. A Large ADU is allowed only on a lot with a single-family home and can be inside the house, attached, or in a detached accessory building [8].
Requirements for both types
- Floor plans are required for new units, plus elevations and an engineered site plan for additions or new structures.
- Lot coverage and dimensional rules of Section 5.4 apply. A Large ADU in an accessory building built after April 28, 2025 must meet main-building setbacks.
- One water and sewer service per lot, use of the existing driveway, a permanent foundation (no RVs or trailers), and Historic District Commission approval of exterior changes in the Historic District.
- One off-street parking space for a Standard ADU unless you're within half a mile of the Manchester commuter rail station [4]. Large ADUs follow the general parking rules in Section 6.1.
- Only one Standard ADU per lot [5], a Large ADU isn't allowed on a lot that already has an ADU, and neither can be sold separately from the main home.
Rental limits
Short-term rentals (under G.L. c. 64G) aren't allowed in either kind of ADU [6], and a Large ADU can't be leased for less than six months [7]. The bylaw has no owner-occupancy requirement. State law lets towns restrict short-term rental of ADUs.
State law
The Standard ADU tracks the state's protected ADU (by right, 900 sq ft cap, one parking space at most). State law caps a protected ADU at 900 sq ft, so the special permit for a Large ADU is consistent with it. State law also bars parking requirements within half a mile of a bus or ferry station, not just commuter rail, so it may override the parking rule for some lots.
Next steps
- Measure your home's gross floor area: a Standard ADU (by right) can be up to half of it or 900 sq ft, whichever is smaller.
- Prepare architectural floor plans, plus exterior elevations and an engineered site plan if you're adding on or building a new structure.
- Apply for a building permit with the Building Department (978-526-2010); for a Large ADU, first get a special permit from the Zoning Board of Appeals.
- If you're in the Historic District, get Historic District Commission approval for exterior changes; if near wetlands, check with the Conservation Commission.
Common questions
- Can I build an ADU in Manchester-by-the-Sea, Massachusetts?
- Yes. The 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.
- Can I build a larger ADU in Manchester-by-the-Sea, Massachusetts?
- A Large ADU, up to 1,200 sq ft, needs a special permit from the Zoning Board of Appeals.
- Does an ADU need parking in Manchester-by-the-Sea, Massachusetts?
- A Standard ADU needs 1 off-street space, unless within 1/2 mile of the commuter rail station.
- Can I rent my ADU on Airbnb in Manchester-by-the-Sea, Massachusetts?
- No. Short-term rentals are not permitted in any ADU.
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
- Section 2 Definitions, Standard Accessory Dwelling Unit, Zoning By-law (compilation dated April 27, 2026), p. 15
Standard Accessory Dwelling Unit: A self-contained housing unit, inclusive of sleeping, cooking and sanitary facilities on the same Lot as a Principal Dwelling, subject to otherwise applicable dimensional and parking requirements, that: (a) maintains a separate entrance, either directly from the outside or through an entry hall or corridor shared with the Principal Dwelling sufficient to meet the requirements of the Building Code for safe egress; (b) is not larger in Gross Floor Area than ½ the Gross Floor Area of the Principal Dwelling or 900 square feet, whichever is smaller.
- Section 4 Table of Use Regulations, E. Accessory Uses 6-7, Zoning By-law (compilation dated April 27, 2026), p. 25
6. Standard Accessory Y Y Y Y Y Y Y N N N Dwelling Unit (12) 7. Large Accessory ZBA ZBA ZBA ZBA ZBA ZBA N N N N Dwelling Unit (13)
- Section 2 Definitions, Large Accessory Dwelling Unit, Zoning By-law (compilation dated April 27, 2026), p. 13
unit larger than a Standard Accessory Dwelling Unit but is not larger in Gross Floor Area than ½ the Gross Floor Area of the Principal Dwelling or 1200 square feet, whichever is smaller.
- Sec. 9.1.2.2(2), Zoning By-law (compilation dated April 27, 2026), p. 67
2. One off-street parking space is required for Standard Accessory Dwelling Units, beyond one half mile from the Manchester Commuter Rail Station.
- Sec. 9.1.2.2(3), Zoning By-law (compilation dated April 27, 2026), p. 67
3. Only one Standard Accessory Dwelling unit shall be permitted on a lot.
- Sec. 9.1.2.2(1), Zoning By-law (compilation dated April 27, 2026), p. 66
1. Short-term rentals as defined in G.L. c. 64G, §1 shall not be permitted in any Standard Accessory Dwelling Unit.
- Sec. 9.1.3.2(6), Zoning By-law (compilation dated April 27, 2026), p. 68
6. Large Accessory Dwelling Units shall not be leased for a period of less than six months.
- Sec. 9.1.3.2(4), Zoning By-law (compilation dated April 27, 2026), p. 68
4. The unit may be within an existing residential structure, attached to, or in a detached accessory structure.