Accelerating Production of ADUs through Research Backed Program Design

The lack of affordable housing is a significant concern for many Boston residents. ADUs provide an opportunity to add housing without changing the character of the residential fabric. 

In addition, ADUs help homeowners remain in their homes by generating steady rental income, supporting multigenerational family arrangements, and providing opportunities for aging in place. 

Our goal is for ADUs to:

• Increase affordable housing options in Boston neighborhoods.
• Create opportunity for wealth generation through steady rental income. 
• Support multigenerational family arrangements. 

• Provide opportunities for aging in place.

The Housing Innovation Lab and Mayor’s Office of Housing launched a few pilot and demonstration projects that have expanded public discourse about ADUs in Boston, helped uncover barriers for residents who want to create an ADU, and created opportunities for streamlining the process.

ADU 1.0 (Nov 2017- May 2018)

The ADU 1.0 Pilot allowed owner-occupants of 1-, 2-, and 3-family homes in East Boston, Mattapan, and Jamaica Plain to carve out space within their home to build an ADU. 

In under 12 months, the pilot program worked with over 50 eligible applicants as they moved from ADU design to construction. ADU pilot applicants ranged in age, income, race, and ethnicity. 

Within the first year of the pilot, 12 applicants received building permits, and two residents completed construction. The success of this Pilot led to the expansion of the Zoning Amendment to the remaining Boston neighborhoods.

Read more about the ADU 1.0 Pilot

Plugin House (May 2018)

The Plugin House, an easily assembled compact unit, was placed on City Hall Plaza in May 2018. The exhibit welcomed over 2,000 visitors in a one week period. Comments collected from visitors overwhelmingly supported allowing this type of housing in Boston. 

Read more about the Plugin House

ADU 2.0 (2021-2022)

The ADU 2.0 Pilot provided support to homeowners interested in turning existing exterior structures—like carriage houses and underutilized garages—into livable space. 

In 2021 and 2022, we hosted two cohorts with eight residents each. We worked with these homeowners to understand the barriers, gaps, and opportunities to create ADUs in existing exterior structures. 

Over the course of four months, participants were offered technical assistance through three workshops to help them prepare and submit a long-form building permit with Inspectional Services and request variances (if needed) from the Zoning Board of Appeals. Learnings from these cohorts helped to push regulatory change to allow backyard ADUs by right in Boston, for example clear fire and building code guidelines for attached and detached ADUs.

ADU 3.0 (2023-present)

In 2023, though homeowner interest in ADUs was significant, with over 1,000 people attending design workshops since the start of the program, less than 200 had been built. Also, while the promise of enabling ADUs includes wealth generation for low-to-moderate income (LMI) households, data from other regions showed projects primarily benefited high-income households. This led the City to question what more could be done to accelerate ADU production in a way that benefits a diverse range of citizens.

MONUM collaborated with the Harvard Graduate School of Design Laboratory for Values in the Built Environment to understand what barriers and opportunities exist to support homeowners with ADU development. The City and Research team surveyed homeowners interested in ADUs, completed expert interviews, facilitated in-person user research, and facilitated working sessions with local banks. This multi-pronged research led to the design and implementation of new tools to remove friction and unblock ADU development for homeowners, including improved user experience for the ADU toolkit webpage and new ADU financial assistance program.

• Making big changes can help to start small and gather supporters along the way. The ADU 1.0 pilot in only three neighborhoods helped demonstrate that homeowners were interested in this type of housing and generated a group of people interested in speaking at public meetings and hearings required to scale the initiative citywide.
• Even when something seems like a failure, the information about why it didn’t work provides essential learnings. Unfortunately, none of the 16 ADU 2.0 pilot homeowners were able to get a permit within a year of participating in the pilot. However, we learned that the most significant barrier was complex fire code regulations and were able to work with the fire department to develop clear guidance that now makes these types of ADU possible. 
• Make new ideas concrete and show what they could look like. The Plugin House demonstration helped the public visualize what a backyard ADU could look like and helped them imagine in their neighborhood.
• Talking to residents illuminates barriers and opportunities. User research conducted as part of ADU 3.0 helped identify webpage improvements and informed the development of financial products as opportunities to reduce friction for homeowners.

We frequently hear from residents who want to build ADUs external to the main building, either as attached (additions) or detached structures (backyard cottages). 

The current zoning relief only applies to internal ADUs (mostly basements and attic renovations). We are working to expand ADUs zoning relief, financing tools, and development support to help more homeowners access this opportunity.

Sign up to stay up to date



To learn how to move forward with the process of adding an interior ADU to your property and how to apply for a 0% loan to build your approved design, visit the ADU Program webpage.