Accessory Dwelling Units (ADUs) in the Commonwealth

Written by

Accessory Dwelling Units (ADUs)

Now Allowed By Right in Massachusetts

Small guest house in light blue with a white trimmed window, a wooden front door with mini windows, a wood awning, and a blue floored front porch with a white chair with a flowered pillow siting on the front porch.

Photo Credit: AdobeStock_145314013

Accessory Dwelling Units (ADUs) in the Commonwealth
CHANGE FONT SIZE

MAPC >> Resources >> Housing >> Accessory Dwelling Units (ADUs) in the Commonwealth

Upcoming Webinar - Register to Join Us!

Please join MAPC staff and local municipalities for this virtual opportunity to learn tips for implementing the new Accessory Dwelling Units (ADU) State Law.

Tips for Implementing Accessory Dwelling Units Legislation in Your Community
Monday, December 9, 2024 | 12:00 p.m.

Register to Join Us

ADUs are an important tool in addressing local housing needs – they provide smaller, more affordable housing choices.

In August 2024, Massachusetts passed the Affordable Homes Act, which, among other things, legalized Accessory Dwelling Units (ADUs) by right in the entire state.

This legislation will go into effect on February 2, 2025. 

ADUs can support intergenerational living, residents with caregiver needs, young people, aging residents, and so many more. 

What Does the New State Law Say?
Resources for Municipalities

Questions? Please contact:
Gwendolyn Hellen-Sands
Regional Housing Planner II
[email protected]

Alexis Smith
Principal Regional Housing and Land Use Planner
[email protected]

Go to Section:

What Does the New State Law Say?

What are ADUs?

Why Does Greater Boston Need More ADUs?

Increasing Affordable Housing Through ADUs

Resources for Municipalities

Research, Trends, and Opportunities

ADUs in the News

Homeowner and Property Owner Resources

Frequently Asked Questions (FAQs) - coming soon!

What Does the New State Law Say?

The law establishes limits on how ADUs can be regulated, including requiring by-right approval for the first ADU on a property; prohibiting occupancy requirements; and limiting parking requirements. The law does allow communities to regulate whether ADUs are used as short-term rentals (vacation homes).  

The ADU law goes into effect after February 2, 2025, and zoning provisions that are inconsistent with MGL c. 40A Section 3 may be unenforceable after this date. An application for an ADU in a single-family zoning district that is consistent with MGL 40A definition and requirements should be accepted and acted on consistent with state statute.  Municipalities are encouraged to review their zoning and identify provisions that are not consistent with the law. (Source: EOHLC ADU FAQs: Accessory Dwelling Units (ADUs) - FAQs | Mass.gov)

Read the Full Legislation

What Does This Mean for Cities and Towns?

The newly passed state legislation requires that all cities and towns allow ADUs by-right in single-family residential zoning districts.

What are ADUs?

Accessory Dwelling Units (ADUs) are small homes inside or attached to a single-family home or in a detached structure, such as a garage or carriage house. Sometimes known as granny flats, in-law apartments, or secondary dwelling units, they include a kitchen, bath, usually at least one bedroom and a separate entrance.  

A lower level ADU. A peach stucco house with white window trim and doors. Bottom level of the home has vanilla colored garage doors that open from the front. There are three green patio chairs on the driveway, and plants and greenery surrounding the house.

Lower Level ADU

Photo Credit: Melissa Stanton, take from AARP's website

A lower level ADU. A peach stucco house with white window trim and doors. Bottom level of the home has vanilla colored garage doors that open from the front. There are three green patio chairs on the driveway, and plants and greenery surrounding the house.
Internal ADU. An orange one level home. Stairs on the side of the home lead into the studio apartment. Stairs in the center of the home lead to the main entrance of the main home. There are rocks, plants, and grass surrounding the house.

Internal ADU

Photo Credit: Photo courtesy of Billy Ulmer, take from AARP's website

Internal ADU. An orange one level home. Stairs on the side of the home lead into the studio apartment. Stairs in the center of the home lead to the main entrance of the main home. There are rocks, plants, and grass surrounding the house.
ADU House. A green one-level house with a sidewalk coming from the main entrance, and a sidewalk going to a side entrance of an ADU. There are plants in front of the house.

Attached ADU

Photo Credit: Michael Daniel, taken from AARP's website

ADU House. A green one-level house with a sidewalk coming from the main entrance, and a sidewalk going to a side entrance of an ADU. There are plants in front of the house.
Two photos side by side. The photo on the left is of a multi-colored house under construction. There are lifts under the home to bring it up a level. The photo on the right is of the completed constructed house with the lower level that was added completely done. There are trees, some plants, and grey sidewalks and direct surrounding the house.

Basement ADU

Photo Credit: Communitecture and Chris Nascimento, taken from AARP's website

Two photos side by side. The photo on the left is of a multi-colored house under construction. There are lifts under the home to bring it up a level. The photo on the right is of the completed constructed house with the lower level that was added completely done. There are trees, some plants, and grey sidewalks and direct surrounding the house.
ADU of a separate house dwelling with a separate outside entrance over two garages. The house is white, two-story, with blue trim.

Garage Apartment ADU

Photo Credit: Mara Owen, taken from AARP's website

ADU of a separate house dwelling with a separate outside entrance over two garages. The house is white, two-story, with blue trim.
A small, blue, detached ADU. It has an orange front door, numerous windows, small planters in the front. It has trees and a wood fence in the background.

Detached ADU

Photo Credit: AccessoryDwellings.org, taken from AARP's website

A small, blue, detached ADU. It has an orange front door, numerous windows, small planters in the front. It has trees and a wood fence in the background.

Why Does Greater Boston Need More ADUs?

Housing is unaffordable and in short supply across Greater Boston, and we are particularly lacking in smaller housing choices.

ADUs are a low-impact way to diversify housing options in all communities, provide more affordable homes for young families or older adults, and help current homeowners with additional income through rent. Accessory homes are so unobtrusive that they usually can’t be seen from the street. ADUs can:

Icon of two blue homes - a larger and smaller one. Over the top of each house in a dark green colored bubble are light green money symbols.

Provide Less Expensive Housing Choices

  • Cost less than a new single-family home on a separate lot, thus provide options for low- and moderate-income residents 
  • Help seniors stay in their community and “age in place” by renting out their ADU or downsizing and living in it themselves
  • Provide a smaller housing option to meet the growing needs of empty nesters, smaller families, and young adults 

Note: ADUs offer lower-cost rental options, often serving as naturally occurring affordable housing (NOAH). ADUs are not subsidized affordable housing, which is restricted for the exclusive use of lower income households. It is possible to apply deed restrictions to ADUs to create more affordable housing.

Icon of four blue different sized and structured homes. In front of each home are tiny dark green figures representing people.

Provide Homeowners with More Options to:

  • Downsize while staying on their property and live in the ADU 
  • House a caretaker on their property 
  • House their children or parents 
  • Generate supplemental income (from renting the ADU) to help homeowners afford to stay in their primary home
Icon of six different transparent boxes outlined in blue. In each box are different sized and shaped blue boxes and rectangles. In four of the six, there are also green different shaped boxes, circles, and rectangles. Some of the green figures are close to or covering part of the blue boxes. One is far away from the blue box.

Have a Low Impact on the Environment and Neighborhood

  • More compact, infill development promotes more walkable, compact neighborhoods and reduces development pressures on open space
  • Minimal construction impacts due to scale of ADUs
  • Leverages existing infrastructure, saving municipal funds potentially
  • Gentle density designed and maintained by homeowners 

Increasing Affordable Housing through ADUs

Greater Boston needs more housing generally, but deed-restricted Affordable Housing is even more critical as the number of cost-burdened renters is staggeringly high (over 50% of renters pay more than 30% of their income on housing). Cities, towns, and nonprofits are all finding ways to leverage ADUs to increase the share of Affordable Housing in communities. 

Aerial photo of Salem, Massachusetts. Numerous roads with cars on them, a church, other buildings, and trees.
Photo Credit: AdobeStock_880938010

Salem, MA | Photo Credit: AdobeStock_880938010

Best Practice: Salem
The City of Salem allows affordable accessory dwelling units by right.  The City achieves this through ensuring that ADUs are allowed by right, but they are required to be rented at or below 70% of the fair market rent limit.

Homeowners in Salem who have an ADU on their property and are renting it at or below the 70% rate are eligible for a tax incentive that exempts the value of the ADU from their property taxes. This incentive encourages the creation and rental of affordable ADUs throughout the city. Note that aspects of the City’s ADU policy may need to be amended to be consistent with the state law. 

Learn more about Salem's ADU policies:
Facts about Accessory Dwelling Units (ADUs) | salemma 

Small guest house in light blue with a white trimmed window, a wooden front door with mini windows, a wood awning, and a blue floored front porch with a white chair with a flowered pillow siting on the front porch.
Cozy country style guest house

Photo Credit: AdobeStock_145314013

Research: Opportunities for Nonprofits
A study published in September of 2024 by Haewon Wa with support from the Joint Center for Housing Studies at Harvard University and Neighborworks America explored the role that non-profits can play in the creation of affordable accessory dwelling units. 

The study focuses on four case study programs that supported ADU creation in various states and for diverse resident populations. Non-profits were found to be helpful in two main areas of ADU creation: supporting homeowners to construct new or renovate existing ADUs on their property and advocating for policies that allow informal ADUs to be formalized.  

Access the Study: Nonprofit Accessory Dwelling Unit (ADU) Programs as Affordable Housing Strategies 

 

Resources for Municipalities

Several cities and towns in the MAPC region have existing ADU ordinances or bylaws that may need to be amended to be consistent with the new state law. Others may not have any existing ADU regulations but will want to create them to better administer the new law. MAPC is working on updated guidance to help communities amend or create new bylaws/ordinances. Existing ADU resources and examples from other MA communities that may be helpful are linked below.

More comprehensive guidance is forthcoming! 

Icon of an outline of a house in light green, over a dark blue background in the shape of a circle.

How Nonprofits Are Using Accessory Dwelling Units as an Affordable Housing Strategy
(Harvard Joint Center for Housing Studies, 2024) 

ADUs: Lessons for Massachusetts from Around the Country
(Harvard Joint Center for Housing Studies, 2023) 

Overcoming Barriers to Bringing ADU Development to Scale
(Enterprise, 2020) 

State of Zoning for Accessory Dwelling Units
(Pioneer Institute, 2018)  

ADUs in the News

Icon of A light green outlined piece paper with horizontal lines on it and the word "News" at the top. Coming out the left side of the paper is a box with an outline of earth in it. The background of the icon is dark blue and in the shape of a circle.

Governor Maura Healey Signs Most Ambitious Legislation to Address Housing Costs in State History
August 6, 2024 | Source: Mass.gov

ADUs ‘by Right’ Are Now the Law in Massachusetts; Gov. Healey Signs AARP Backed Housing Bill
August 6, 2024 | Source: AARP 

Massachusetts now has a 'historic' $5.2 billion housing law on the books. But how far will it go?
August 6, 2024 | Source: The Boston Globe

New ADU Tools May Unlock Affordable Housing in Your Backyard
September 26, 2024 | Source: American Planning Association Planning Magazine 

Homeowner and Property Owner Resources

Icon of a light green outline of a house with a person reading a book inside of the house. It's on a dark blue background in the shape of a circle.

Building an ADU
(Building an ADU) 

All About Accessory Dwelling Units
(AARP) 

Frequently Asked Questions (FAQs)

Icon of two light green outlined speech bubbles. A question mark is in one. Three horizontal lines is in the other. They are over a dark blue background in the shape of a circle.

Coming soon!