Can I build an ADU in Salem, Massachusetts?
Yes. Salem allows one accessory dwelling unit (attached or detached) by right on a lot in the RC, R1, R2 and R3 residential districts with just a building permit from the Building Inspector. The ADU can be no larger than 900 sq ft or half the main home's floor area, whichever is smaller, needs no parking, and neither the ADU nor the main house may be used as a short-term rental.
| Approval needed | Building permit from the Building Inspector; no special permit [1] |
| Allowed districts | RC, R1, R2, R3, B1, B5 and NRCC (not B2, B4, I or BPD) [2] |
| Max size | 900 sq ft or half the main home's gross floor area, whichever is smaller [3] |
| Parking | No minimum parking requirement [4] |
| Detached ADU setbacks | 5 ft from side and rear lot lines; 10 ft from other buildings; not in the required front yard [5] |
| Short-term rentals | Prohibited in both the ADU and the main house [6] |
| Number per lot | One by right; lots with 2-5 units may add one per unit by special permit [7] |
| Rent cap | Optional: owners may cap rent at 70% of HUD Fair Market Rent to qualify for a tax exemption [8] |
Where ADUs are allowed
Salem's Table of Principal and Accessory Use Regulations lists "Accessory Dwelling Unit (subject to Section 3.2.8)" as allowed by right ("Y") in the RC, R1, R2 and R3 residential districts, as well as B1, B5 and NRCC [2]. Section 3.2.8 is administered by the Building Inspector through the building permit, and no special permit is needed for one ADU [1]. The application must be signed by all record owners of the lot (all unit owners for a condominium) and include scaled floor plans and elevations of both units.
Size and design
The ADU can be attached or detached, but may not exceed half the gross floor area of the main home or 900 sq ft, whichever is smaller [3]. The ADU and the main house must stay in common ownership, and a detached ADU that is not owner-occupied needs separate utility service.
Setbacks for detached units
A detached ADU can't sit in the required front yard or the 5-foot side yard of a corner lot. It must be at least 5 feet from the side and rear lot lines and 10 feet from any other building [5]. Otherwise the Section 4.1 dimensional rules apply. On a nonconforming lot or house, the Zoning Board of Appeals may need to find the ADU is not substantially more detrimental, but no special permit is required.
Parking, rentals and rent
There is no minimum parking requirement [4]. Short-term rentals are prohibited in both the ADU and the main dwelling [6]. Earlier versions of the ordinance required ADUs to rent at no more than 70% of HUD Fair Market Rent; the May 2025 amendment makes that cap optional, as a way to qualify for a property tax exemption [8]. The city's ADU FAQ page still calls the cap mandatory; rely on the ordinance. One ADU is allowed by right per lot; lots with 2 to 5 homes may add one ADU per unit by special permit, with detached units capped at 18 feet [7].
State law
Salem's rules largely track the state ADU law in effect since February 2, 2025 (no owner-occupancy, no special permit, no parking for one ADU), and Section 3.2.8 says the state definitions in 760 CMR 71.02 control if there is a conflict. State law bars "unreasonable" restrictions on a protected ADU, so it may override some of Salem's extra conditions, such as requiring every record owner to sign the application, common ownership of both units, separate utilities for a detached ADU that isn't owner-occupied, and the short-term-rental ban on the main house (state law expressly lets cities restrict short-term rentals of the ADU itself). Confirm current details with Inspectional Services.
See how Salem compares with 8+ other Massachusetts towns on accessory dwelling units (adus) →
Next steps
- Check your zoning district on Salem's zoning map (ADUs are by right in RC, R1, R2 and R3).
- Have plans drawn to scale showing floor plans and elevations of the main house and the ADU, and confirm the ADU is no more than 900 sq ft or half the main home's floor area.
- Get every record owner of the lot (or every condo unit owner) to sign the building permit application, then file it with Inspectional Services (98 Washington St, 978-619-5641).
- Don't move anyone in until the Building Inspector issues a certificate of occupancy; obtain a certificate of fitness if renting.
- If you want the property tax exemption, ask the Assessor's Office about the optional 70%-of-Fair-Market-Rent restriction.
Common questions
- Can I build an ADU in Salem, Massachusetts?
- Yes. Salem allows one accessory dwelling unit, attached or detached, by right in the RC, R1, R2 and R3 residential districts (and B1, B5 and NRCC) with just a building permit from the Building Inspector. No special permit is needed for one ADU.
- How big can an ADU be in Salem, MA?
- A Salem ADU can be no larger than 900 sq ft or half the main home's gross floor area, whichever is smaller. A detached ADU must be at least 5 feet from side and rear lot lines, 10 feet from other buildings, and can't sit in the required front yard.
- Does a Salem, MA ADU need parking?
- No. Salem's ADU rules have no minimum parking requirement.
- Can I Airbnb my ADU in Salem, Massachusetts?
- No. Salem's zoning prohibits short-term rentals in both the ADU and the main house. State law lets cities restrict short-term rentals of ADUs, though whether the ban can also reach the main house is less clear.
- Is there a rent cap on ADUs in Salem, MA?
- It depends. The May 2025 amendment made the cap optional: owners may cap rent at 70% of HUD Fair Market Rent to qualify for a property tax exemption. The city's ADU FAQ page still calls the cap mandatory, but the ordinance controls.
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. 3.2.8(4)(k) Accessory Dwelling Units, Zoning Ordinance Sec. 3.0 Use Regulations (3.1 Table of Principal Uses, 3.2 Accessory Uses incl. 3.2.2 Home Occupations, 3.2.4 accessory buildings, 3.2.5 Swimming Pools, 3.2.7 Urban Agriculture, 3.2.8 Accessory Dwelling Units), p. 1
Where the lot or principal dwelling is nonconforming, prior to issuance of a building permit or Certificate of Occupancy, Section 3.3 and G.L. c. 40A, §6 shall apply and a finding by the Zoning Board of Appeals, acting on a majority vote, that the accessory dwelling unit will not be substantially more detrimental than the existing nonconforming structure to the neighborhood may be required. No special permit shall be required.
- Sec. 3.1, Table of Principal and Accessory Use Regulations, E. Accessory Uses, Zoning Ordinance Sec. 3.0 Use Regulations (3.1 Table of Principal Uses, 3.2 Accessory Uses incl. 3.2.2 Home Occupations, 3.2.4 accessory buildings, 3.2.5 Swimming Pools, 3.2.7 Urban Agriculture, 3.2.8 Accessory Dwelling Units), p. 1
Accessory Dwelling Unit (subject to Section 3.2.8)
- Sec. 3.2.8(4)(b), Zoning Ordinance Sec. 3.0 Use Regulations (3.1 Table of Principal Uses, 3.2 Accessory Uses incl. 3.2.2 Home Occupations, 3.2.4 accessory buildings, 3.2.5 Swimming Pools, 3.2.7 Urban Agriculture, 3.2.8 Accessory Dwelling Units), p. 1
The accessory dwelling unit shall be no larger in Gross Floor Area than half the Gross Floor Area of the Principal Dwelling or nine hundred (900) square feet, whichever is smaller.
- Sec. 3.2.8(4)(a), Zoning Ordinance Sec. 3.0 Use Regulations (3.1 Table of Principal Uses, 3.2 Accessory Uses incl. 3.2.2 Home Occupations, 3.2.4 accessory buildings, 3.2.5 Swimming Pools, 3.2.7 Urban Agriculture, 3.2.8 Accessory Dwelling Units), p. 1
There shall be no minimum parking requirement for an accessory dwelling unit.
- Sec. 3.2.8(4)(n), Zoning Ordinance Sec. 3.0 Use Regulations (3.1 Table of Principal Uses, 3.2 Accessory Uses incl. 3.2.2 Home Occupations, 3.2.4 accessory buildings, 3.2.5 Swimming Pools, 3.2.7 Urban Agriculture, 3.2.8 Accessory Dwelling Units), p. 1
No detached accessory dwelling unit shall be located nearer than five (5) feet to any side lot line (side lots in this instance refer to a projected line starting from the front lot line, terminating at the rear lot line parallel five (5) feet from the side) or five (5) feet from the rear lot line, and shall not be located closer than ten (10) feet to any other building on the same lot or any abutting lot.
- Sec. 3.2.8(4)(i), Zoning Ordinance Sec. 3.0 Use Regulations (3.1 Table of Principal Uses, 3.2 Accessory Uses incl. 3.2.2 Home Occupations, 3.2.4 accessory buildings, 3.2.5 Swimming Pools, 3.2.7 Urban Agriculture, 3.2.8 Accessory Dwelling Units), p. 1
Short term rentals, as defined in G.L. c. 64G, are prohibited in both the accessory and principal dwelling units.
- Sec. 3.2.8(4)(q), Zoning Ordinance Sec. 3.0 Use Regulations (3.1 Table of Principal Uses, 3.2 Accessory Uses incl. 3.2.2 Home Occupations, 3.2.4 accessory buildings, 3.2.5 Swimming Pools, 3.2.7 Urban Agriculture, 3.2.8 Accessory Dwelling Units), p. 1
There shall only be one (1) accessory dwelling unit by right on a lot. A lot with two (2) to five (5) principal dwelling units may have one (1) accessory dwelling unit per principal dwelling unit by special permit per Section
- Sec. 3.2.8(4)(p), Zoning Ordinance Sec. 3.0 Use Regulations (3.1 Table of Principal Uses, 3.2 Accessory Uses incl. 3.2.2 Home Occupations, 3.2.4 accessory buildings, 3.2.5 Swimming Pools, 3.2.7 Urban Agriculture, 3.2.8 Accessory Dwelling Units), p. 1
A property owner may choose to restrict the rent, including the utilities, of the accessory dwelling unit to seventy (70) percent of the established Fair Market Rent limit for the City of Salem as determined annually by the United States Department of Housing and Urban Development, to be eligible for a tax exemption pursuant to Section 8 of Chapter 150 of the Acts of 2024.