Can I build an ADU in Hingham, Massachusetts?
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.
| Where allowed | Permitted (P) in Residence A, B, C and E; prohibited where single-family homes aren't allowed [1] |
| Max size | 1/2 of the main home's gross floor area or 900 sq ft, whichever is smaller [2] |
| Number per lot | 1 [4] |
| Extra parking | 1 space (none within 0.5 mile of a transit station) [4] |
| Minimum rental/occupancy term | 30 days; no short-term rentals [6] |
| Owner-occupancy | No owner-occupancy requirement in Section V-K [2] |
Where ADUs are allowed
The Schedule of Uses lists "Accessory Dwelling Units in connection with a Principal Dwelling, subject to Section V-K" as a permitted use (no special permit) in Residence A, B, C and E [1]. It's prohibited in Residence D and the business, office, industrial and waterfront districts, which mostly don't allow single-family homes either.
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 house. It needs a separate entrance (directly outside, or through a shared hall that meets Building Code egress rules), and it can't be larger than half the main home's gross floor area or 900 sq ft, whichever is smaller [2]. It can be inside the house, attached, or in a detached accessory building such as a garage.
Design and dimensional rules
To get a building or occupancy permit, the ADU must meet the district's front, side and rear setbacks and height limits, though it may go inside a lawfully existing nonconforming structure [3]. Stairs to an upper-floor ADU must be enclosed within the building's walls, except that the Building Commissioner may allow an open rear stair on an existing building, and any new entrance must be on the side or rear [3]. You need one parking space beyond what the main house requires, or none within 0.5 mile of a transit station, and only one ADU is allowed per lot [4].
Conditions on every permit
The main house and ADU can't be sold or transferred separately [5]. Both have a minimum occupancy or rental term of 30 days and can't be used as a short-term rental [6].
State law
The by-law has no owner-occupancy requirement and allows ADUs by right, which matches the state ADU law that took effect in February 2025. State law also lets towns restrict short-term rental of ADUs.
See how Hingham compares with 8+ other Massachusetts towns on accessory dwelling units (adus) →
Next steps
- Check your zoning district on the town zoning map; ADUs are permitted in Residence A, B, C and E.
- Confirm the unit meets the size cap (half the main home's gross floor area or 900 sq ft, whichever is smaller) and the district's setbacks and height limits.
- Plan one off-street parking space for the ADU (unless you're within 0.5 mile of a transit station).
- Apply for a building permit with the Building Department (781-741-1420); if you're on septic or near a wetland, check with the Board of Health and Conservation Commission first.
Common questions
- Can I build an ADU in Hingham, Massachusetts?
- 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.
- How big can an ADU be in Hingham, Massachusetts?
- No bigger than half the main home's floor area or 900 sq ft, whichever is smaller.
- Does an ADU need parking in Hingham, Massachusetts?
- Yes, one extra space, though none is needed within 0.5 mile of a transit station.
- Can I rent an ADU short term in Hingham, Massachusetts?
- No. ADUs can't be used as short-term rentals, and the minimum rental term is 30 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
- Section III-A, Schedule of Uses, 1.9, Zoning By-Law (revised through April 28, 2026), p. 28
1.9 Accessory Dwelling Units in connection with a Principal Dwelling, subject to Section V-K
- Section V-K, 2. Definitions (Accessory Dwelling Unit), Zoning By-Law (revised through April 28, 2026), p. 138
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; and
- Section V-K, 3.b (Dimensional and Design Requirements), Zoning By-Law (revised through April 28, 2026), p. 139
The Accessory Dwelling Unit shall comply with building dimensions, including the front, side or rear yard setback and height limitations for the applicable Zoning District. Notwithstanding the foregoing, an Accessory Dwelling Unit may be located within a lawfully existing nonconforming structure.
- Section V-K, 3.d-e (Dimensional and Design Requirements), Zoning By-Law (revised through April 28, 2026), p. 139
In addition to the minimum required parking spaces for a Principal Dwelling, the parking requirement for an Accessory Dwelling Unit is one space, provided however, that no parking space is required for an Accessory Dwelling Unit located within 0.5 miles of a Transit Station as defined in 760 CMR 71. e. Only one Accessory Dwelling Unit shall be permitted per Lot.
- Section V-K, 4.a (General Conditions), Zoning By-Law (revised through April 28, 2026), p. 139
Neither the Principal Dwelling nor the Accessory Dwelling Unit may be sold or otherwise conveyed or transferred separately from the other.
- Section V-K, 4.b (General Conditions), Zoning By-Law (revised through April 28, 2026), p. 139
The Principal Dwelling and Accessory Dwelling Unit shall have a minimum occupancy or rental term of 30 days and shall not be used as a Short-term Rental.