Accessory Dwelling Units (ADUs)

An accessory dwelling unit is a small living space located on the same lot as another home. The ADU law allows property owners to build an ADU by-right.

ADUs can be set up inside an existing home. You can convert a basement into an apartment. You can attach an ADU to a primary residence as an addition. An ADU can be fully separate, like a cottage or converted garage in a backyard. ADUs can offer low-cost housing choices for a family member to stay in their community. ADU residents cannot be required to be related to the owner. ADUs give more options for older adults or people with disabilities to have caregivers live close by. PCAs, home health care or other home care workers can come in to help with care. People can downsize while remaining in their community.

A Protected Use ADU in Massachusetts is a small, secondary living unit (up to 900 sq ft). It is permitted “by-right” in single-family residential zones.

Protected Use ADUs can be permitted in property that has more than one unit such as a duplex, triple decker, or other multi-family home. You will need to check with your town or city Zoning Board for details. Protected Use ADUs are allowed by right in all zoning districts in a city/town that permit single-family homes to be built by right or special permit. This is subject to reasonable regulations.

The ADU law and regulations do not allow a town or city to regulate who can live in a Protected Use ADU.

Zoning laws vary by town or city in Massachusetts.

Modular Dwelling Units may be purchased. They can be transported in one or more sections. ADUs must be set on a foundation that meets the building code and connected to external utilities at the site.

Make sure that you hire a reputable, licensed building contractor to construct or work on your ADU.

Massachusetts homeowners can finance Accessory Dwelling Units (ADUs) through specialized state-backed programs. MassHousing has a new Accessory Dwelling Unit Construction Loan Program that was launched in March 2026.

Accessory Dwelling Units Links

Accessible Dwelling Units

Info is provided by the Massachusetts Executive Office of Housing and Liveable Communities. Here you can find general info about ADUs in Massachusetts. You can also see specific info under each section of the webpage.

Accessory Dwelling Units Frequently Asked Questions

The Executive Office of Housing and Liveable Communities has a list of frequently asked questions and answers. Questions include:

Fact Sheet updated on 4/23/26

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