Amherst, MA
Amherst, Massachusetts Accessory Dwelling Unit (ADU) Rules
Updated: 12/05/2025
What you need to know:
Amherst, like all of Massachusetts since the passage of the 2024 Affordable Homes Act, allows ADUs by right. Each town has slightly different rules surrounding ADUs, but they all must adhere to the framework outlined by the state.
There are two types of ADUs allowed in Amherst - Protected Use ADUs (PADU) and Local ADUs. PADUs are generally in line with Massachusetts state law regarding ADU zoning and requirements, while Local ADUs have their own rules.
Type of Permit Required:
Protected Use ADUs in Amherst are considered by-right, meaning they are allowed in any single-family residential zoning district with a simple building permit.
Local ADUs require administrative approval if the lot has no existing PADU. If the lot already has a PADU, owners can apply for a special permit to build a Local ADU.
ADU Rules in Amherst:
General ADU Rules in Amherst:
No more than one Local ADU and one Protected Use ADU are allowed on the same lot as the main house.
ADUs can be attached, detached, or built within the main house.
Whenever possible, detached ADUs cannot be built closer to the road than the main house.
ADUs need to submit a parking plan to the Building Commissioner and have it approved.
The driveway can be altered or added to, but a new driveway to the street is not typically allowed.
No more than two off-street parking spaces can be added for any ADU.
ADUs must have a separate entrance from the main house - attached ADUs can share an entry hall with the main house, but need a separate entry within the entry hall.
Storage of trash and recycling must be inside the interior of the ADU, in a garage or another accessory outbuilding.
All exterior lighting must be designed and installed to avoid disturbing neighboring properties.
If the owner wants to rent the ADU or their main house, it will have to be registered and permitted in accordance with the Residential Rental Property Bylaw (See here: https://www.amherstma.gov/DocumentCenter/View/24029/Residential-Rental-Property-Bylaw?bidId=).
ADUs shall not have a new driveway or curb cut unless approved by public works.
Protected Use ADU Rules in Amherst:
PADUs can be maximum 900 square feet, or half the Gross Floor Area of the main house; whichever is smaller.
There is no minimum lot size to build a PADU.
PADUs within ½ mile of a transit station do not require additional parking. Properties outside of that area could require additional off-street parking.
PADUs do not require owner-occupancy.
PADUs have less restrictive setback requirements than Local ADUs in Amherst.
Local ADU Rules in Amherst:
Local ADUs can be a maximum of 1200 square feet.
Local ADUs must have a similar architectural style as the main house.
Either the main house or the Local ADU must be occupied by the property owner(s).
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