Affordable Homes Act Policy Spotlight: Accessory Dwelling Units

A Small Change That Can Achieve Big Results

May 22, 2024 - Almost every week, a news article is published that highlights the magnitude of the housing crisis in Massachusetts. Just last month, the New York Times highlighted one phenomenon that planners across Massachusetts hear every day in our communities. Aging residents want to downsize their homes, but they cannot find a new, smaller home that fits their price range and unique needs. Many would love to find a small home in their same community, with minimal maintenance required, and only one level to help with their aging mobility needs.

There are several bills pending before the Massachusetts State Legislature this session that would help the Commonwealth build the housing it needs. These bills include the Governor’s Affordable Homes Act (AHA), which offers meaningful opportunities to partner with cities and towns, policies, and funding to respond to this crisis.

Enter the accessory dwelling unit.

One Solution: Accessory Dwelling Units

Accessory dwelling units (ADUs) are apartments located inside 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, and usually at least one bedroom.

ADUs were prevalent before World War II throughout American cities and towns, often housing in-laws and extended family members. However, restrictive policies that prohibited multi-family development largely zoned ADUs out of existence in the post-war era. When we talk about the “character of communities,” it’s important to remember that ADUs have long been a part of the character of communities across Massachusetts.

This only changed as restrictive zoning laws were put in place to exclude low-income residents and residents of color from certain neighborhoods. As a result, it’s now harder for young people to find a modest place to live, harder to support aging relatives or relatives with a disability, and harder to foster the vibrant multi-generational neighborhoods that helped make the Commonwealth what it is today. While prohibitions against ADUs are not the only reason for these challenges, removing these prohibitions is an important part of addressing this history of exclusion and restoring the diversity of housing types necessary to meet residents’ needs.

Beginning in the 1970s, a handful of municipalities began to write ADUs back into their zoning, recognizing them as one important solution to high housing costs. Nationally, Oregon and California are at the forefront of creating flexible zoning to encourage ADUs. More locally, Maine and Vermont have allowed ADUs statewide. This year, Massachusetts has the chance to join these states in allowing ADUs by-right, making it easier for residents to find a modest and affordable home and be closer to loved ones who need support.

Across Massachusetts, 56% of all homes are single-family. [1] That’s over 1.7 million single-family homes that could potentially accommodate an accessory dwelling unit (ADU). Accessory apartments are so unobtrusive that they usually can’t be seen from the street. Over time, even if only 10% of these homeowners chose to build an ADU, that could eventually create 170,000 new homes in Massachusetts that could be affordable. The new homes would meet the needs of aging adults looking to downsize but stay in the same town or near family, younger singles who might be in school or starting their first job, and caregivers for people with disabilities, etc.

In many communities across Greater Boston, the share of single-family homes is even higher; Norfolk, Sharon, Wayland, Sudbury, Middleton, and Wenham are just a few municipal examples where single-family homes comprise more than 85% of the local housing stock. In these suburban communities, lot sizes are often larger, too. Ranging from 1-acre to 3-acres or larger, these lots could easily accommodate an accessory dwelling unit. MAPC explored what smaller housing options like ADUs could look like and where they could better meet residents’ needs in suburban communities through our Living Little project. ADUs were highlighted alongside other smaller housing types like cottage housing, tiny houses, townhouses, and single-family home conversions.

[1] American Community Survey, 2022.