Massachusetts passed the Affordable Homes Act in 2025, which created a “protected use Accessory Dwelling Unit” allowing for the by-right construction of Accessory Dwelling Units (ADUs) on residential lots. The intention behind the passage of this act was to help address the affordable housing shortage statewide and assist municipalities with tools for housing production. According to this act, ADUs must comply with local zoning laws and other reasonable regulations, but give property owners the flexibility to expand in ways they may not have been able to previously.

ADUs must be 900 square feet of living space total (or half the size of the primary home, whichever is smaller). This square footage includes the basement if it is habitable (ie. the ceiling height needs to be over 6’6″). ADUs cannot be larger than this (unless Nantucket votes to make the size requirement more permissive in the future which could potentially happen). Protected Use ADUs must comply with all local regulations, like ground cover requirements, setbacks, septic requirements, and HDC regulations. It gives property owners who already have a house and a cottage on a lot the ability to add a third structure that would not otherwise be allowed.

Nantucket has been a leader in affordable housing. You may recall that Nantucket passed an article at the Annual Town Meeting (ATM) a few years ago, which allowed for tertiary dwellings to be built on certain properties. It seems that the state partly modeled its Protected-Use ADUs off Nantucket’s tertiary dwellings. There are no occupancy requirements for these structures which is different than Nantucket’s tertiary dwelling, which required year-round occupancy to help the island with its housing needs. Towns in the Commonwealth have the ability to regulate whether they are used for short-term rentals in the future, but at this point, that subject has yet to be broached on Nantucket.

Due to the island already allowing tertiary dwellings, at ATM in 2025, Nantucket voted to put a moratorium on the creation of additional tertiary dwellings. The main concern was that the creation of ADUs would open the door for the potential of four dwellings on a property if tertiary dwellings were still allowed in our zoning code. The moratorium on the creation of additional tertiary structures means that the zoning code now allows for three structures maximum on Nantucket (a primary and secondary dwelling and an accessory dwelling unit).

Protected-Use ADUs are permitted by right under the Dover Amendment, which means that the property can be built without a special permit if it satisfies state and local zoning rules. The Dover Amendment was passed in 1950 and covers discrimination in housing (think schools, churches, and daycare facilities). There are many subdivisions on Nantucket with HOA restrictions that prohibit a second dwelling. Homeowners Associations (HOAs) are not covered in the language allowing ADUs. A second dwelling is not technically an ADU, but if a property owner builds a 900 sq. ft. structure and calls it an ADU, will they be allowed in neighborhoods like this? For example, if a property owner in one of these neighborhoods applies for a building permit from the town to build an ADU, the town will issue a building permit, but there is the possibility that the HOA might take exception to it. This is a matter that will unfold in the coming years, and we will need to see how the HOAs respond to determine how ADUs impact development in these neighborhoods.

These are a relatively new concept (just under a year old), so it will be important to stay up to date on how the laws and regulations are evolving. This is a link to the state webpage, which explains the Affordable Homes Act in detail and has a FAQ section for Protected Use Accessory Dwelling Units, which may be helpful in answering any questions you have.

For more Nantucket stories visit our blog at Fisher Real Estate.