Massachusetts embraces backyard homes as housing and climate solution

When Marsha Gleason and her husband decided it was time to downsize from the 2,000-square-foot bungalow where they’d lived for the past 40 years, they didn’t head to Florida or research local retirement communities. Instead, they looked to their own backyard.

The pair sold their house in Northborough, Massachusetts, to their son in 2024 and moved into a compact, super-energy-efficient modular home they’d put up across the driveway from their former abode. Today, Gleason says her new home, though less than half the size of her previous one, has everything she needs: stunning natural light, proximity to family, and really low utility bills.

“I am aging in place in my old neighborhood,” she said. ​“I am just amazed at how economical it is to live here.”

Gleason is among a growing number of Massachusetts homeowners who are embracing accessory dwelling units, or ADUs, as a way to create right-sized housing options in a tight and expensive market. The definition of ADUs is broad. It includes traditional in-law units, apartments built over garages, and small freestanding homes located in a backyard. They can be rented out for additional income, provide homes for caretakers, or, as in Gleason’s case, become an option for aging residents ready for a smaller space.

While ADUs are often discussed as a possible part of the solution for ongoing housing shortages in Massachusetts and beyond, they can also slash energy bills and chip away at the huge chunk of planet-warming pollution created by the building sector.

Those benefits largely derive from ADUs’ small footprint: They simply consume less energy and require less building material, cutting down on the greenhouse gases associated with extracting, producing, and transporting goods like steel and wood.

But other factors play a role, too. Many ADUs are built all-electric, eliminating the combustion of fossil fuels for heating and cooking. These small homes are also typically highly energy-efficient, especially those that are largely prefabricated in factories and assembled on-site. Massachusetts-based Reframe Systems, for example, uses robots in its factories to join pieces with high levels of precision, yielding exceptionally airtight units that hold their temperature well.

“This is allowing us to democratize what a high-performance home would look like and make it more available,” Reframe CEO Vikas Enti said. 

Many ADU factories also use techniques that minimize building-material waste, and some vendors get creative with lower-carbon options. Rare Forms, a home manufacturer in Easthampton, Massachusetts, insulates its prefabricated panels with locally grown straw, locking in much of the carbon the plant captured while growing.

“These ADUs really hit the sweet spot around promotion of housing production in a very sustainable and climate-friendly way,” said Lauren Baumann, director of sustainability and climate initiatives at the nonprofit Massachusetts Housing Partnership.

The push to boost ADUs

Massachusetts is attempting to harness the power of ADUs. In 2024, Gov. Maura Healey (D) signed a housing law that makes the structures legal in 350 of the state’s 351 cities and towns (it does not apply in Boston), and limits the restrictions individual municipalities can impose on such construction. In 2025, more than 1,200 ADUs got permits statewide. That number is generally agreed to be a significant uptick from previous years, though not on pace to reach the state’s goal of 1,600 to 2,000 ADUs built each year through 2030.

Several efforts are underway to speed up that rate. In March, the state introduced a low-cost financing program for the units. And the Massachusetts Housing Partnership and Massachusetts Clean Energy Center each recently launched incentive programs to make it easier for homeowners to add an ADU to their property.

The Housing Partnership’s program gives homeowners access to low-cost feasibility studies. The organization created a network of participating providers who will charge no more than $500 to complete an analysis of a property’s conditions and constraints, local zoning or permitting restrictions, utility needs, design considerations, and a rough cost estimate. The cost to build an ADU typically ranges from $120,000 to $450,000, depending on size and whether the project involves converting an existing space or building a new structure.

“We’ve heard from property owners that there is a lot of interest in ADUs, but ​‘Where do I start?’” said Meredith Boericke, the organization’s ADU director. ​“This helps them to go from concept to actually getting it constructed.”

The Clean Energy Center has its own pair of offerings. The ADU Resource Center is an online repository of information about siting, designing, and building the units. Its ADU Wizard tool lets users look up any property in the state, get an initial assessment of whether an ADU can be built there, and even try out different building footprints on a diagram of the lot.

A second program focuses on the Pioneer Valley, a 69-town region in western Massachusetts. This more involved option gives homeowners one-on-one support as they analyze whether an ADU would work for them, and provides a curated list of manufactured home suppliers. The program, which launched in June, has already completed about 15 consultations, and has five homeowners who are likely to move forward with an ADU.

Patchy rules still hinder growth

Even as new programs pave the way for ADUs, Massachusetts needs to make more changes to truly build momentum, say housing and climate boosters.

The most oft-cited barrier is the state’s approach to permitting and zoning: Each city and town makes its own rules and decisions, creating a complicated regulatory patchwork for builders. Though the 2024 law requires municipalities to allow ADUs up to 900 square feet in single-family zoning districts, it also preserves communities’ ability to impose other rules, such as minimum property-line setbacks, septic requirements, and height limits.

“You still have to learn 351 sets of rules if you want to operate statewide,” said Andrew Mikula, senior housing fellow at the Pioneer Institute, a Boston-based housing and economic development think tank.

The state could speed up ADU construction by following the lead of California, which Mikula said leads the pack in encouraging the housing type. Overriding individual municipalities’ guidelines and standardizing more regulations statewide would make it easier for homeowners and builders to navigate the process.

As advocates continue to push for additional regulatory reform, progress is still being made. Gleason said she has heard of at least three more units in the works in Northborough since hers was built.

“I was paving the way,” she said. ​“It’s such a great concept, and it’s been such a wonderful thing for my family in so many ways.”