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Additional Dwelling Units

We want to streamline the process for homeowners looking to create an additional unit.

The program allows owner-occupants in the City of Boston to carve out space within their homes. They can create smaller, independent units, known as Additional Dwelling Units (ADUs).

The goal of the program is to develop more natural affordable housing options. We can can do this while creating rental income for homeowners. We want homeowners to take advantage of the existing space in their homes. Our program can help people age in place and prevent displacement.

Interested in learning more or applying to the program? Check out the information below: 


BOSTON, MA 02108-2501

Why we did this

Two top priorities for Mayor Walsh and the City of Boston include:

  • lowering the cost of living in Boston, and
  • preventing displacement.

We tried to address both priorities through our pilot (pilot ran Oct 2017 - May 2019). Owner-occupants could carve out space in their home to create a smaller rental unit. Those looking for an apartment would have more options. Homeowners stretched thin by the cost of living in Boston would gain income.

The experiment

We wanted to see if these units increase affordable housing options in Boston.

We hoped to create safe living environments and support family arrangements. We also hoped this would help aging homeowners remain in their homes. Based on the results of the pilot, we hoped to find out the impact these units have on affordability and displacement. We would also get a better idea of the impact of expanding the program. Our final presentation to the Zoning Commission has more information.


Pilot Details
Pilot Zoning and Eligibility

We crafted the zoning language for the program with the help of the Boston Planning & Development Agency. The agency's board approved the amendment, which you can read online. The Mayor signed off on the language in November 2017.

To qualify for a unit, your home must be:

  • three units or less
  • owner-occupied, and
  • in the City of Boston.
Additional Dwelling Unit Toolkit

As part of this program, we developed an Additional Dwelling Unit Toolkit. The toolkit is a guide for homeowners who would like to build their own unit. We walk homeowners through the:

  • permitting
  • design
  • financing, and
  • construction processes.

Additional Dwelling Unit toolkit

Additional Dwelling Unit Loan program

We also plan to offer limited financial support to homeowners looking to build an Additional Dwelling Unit. A zero-interest, deferred equity loan up to $30,000 will be available for eligible homeowners. The loan is through the Boston Home Center's Additional Dwelling Unit Loan Program.

Results and lessons learned

The Additional Dwelling Unit (ADU) program has helped many residents. That's especially true for older adults interested in aging in place and staying in their neighborhoods. We're providing new housing for family members and renters. These ADU program participants ranged in age, income, race, and ethnicity. In addition, many residents want the program to expand to other Boston neighborhoods. You can learn more about the ADU Program and what's next in the ADU Program Report.

ADU+ Carriage Houses Pilot

The Carriage Houses as ADU+ Pilot Program is currently underway. The program explores how empty carriage houses throughout the City can be converted into additional dwelling units (ADUs). The goal is to create affordable housing options for residents priced out of the City's housing market.

carriage house

The Housing Innovation Lab is conducting an inventory of Boston's carriage houses. We're doing this in collaboration with:

This inventory will inform planning for future projects around neighborhood development in Boston. If you would be interested in being a part of this next iteration of our ADU program, please complete the form below:

Carriage House Self Inventory Form

Also, if you are interested in having a more in-depth conversation about your carriage house, please send us an email to We would be happy to chat with you!

Final Outcome

On May 8, Boston Zoning Commission approved a citywide zoning text amendment. This amendment scaled the pilot program citywide and made it permanent. In addition, Mayor Walsh announced funding for the expansion of the ADU program as part of his Fiscal Year (FY20) budget recommendations.

This $650,000 investment will provide zero-interest loans for income-eligible homeowners. For more information see the overview presentation below.

ADU Overview - Citywide Presentation