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Last updated: 4/13/18

Additional Dwelling Unit toolkit

Boston’s ADU program offers more housing options while creating rental income for homeowners. 

The Additional Dwelling Unit (ADU) pilot program is for homeowners in East Boston, Mattapan, and Jamaica Plain. Residents should be able to age in place without worrying about being displaced.  Through the ADU program, they can carve out a space in their home to create smaller, independent units.  

If you're interested in learning more about the status of the pilot program, check out the information below: 

ADU Overview - Citywide Presentation

Have questions? Contact us:

BOSTON, MA 02108-2501
Have questions or comments?

How to apply

There are a few simple steps to apply for this program. Details on the pilot and homeowner eligibility can be found in this section. We also linked to a how-to guide below.  

How-To Guide

Eligibility Checklist

If you answer yes to ALL of the questions below, you are eligible.

  • Do you live in East Boston, Jamaica Plain, or Mattapan?
  • Are you the owner of a one-, two-, or three-family home?
  • Do you live in the property where you want to build the unit?
  • Do you plan to build the unit inside the footprint of your home?
  • If your home is in the FEMA Flood Zone, is the basement or first floor elevation ("Top of Bottom Floor" on an elevation certificate) above the Base Flood Elevation (BFE)?
  • Mayor Walsh and the Boston Zoning Commission approved this 18-month pilot program on November 8, 2017. The program was formally launched in early 2018.
  • In the three pilot neighborhoods, an additional dwelling unit will be allowed by right, provided that it is the addition of no more than one dwelling unit to the existing structure.
  • An additional dwelling unit used as a rental must be registered in accordance with Ch. 9-1.3 of the City of Boston Rental Registry Ordinance at the time of conversion.

Loans for the program

Loans for the program

The Boston Home Center will offer a loan that provides gap funding for qualified program participants.


The loan is zero-percent interest (0%), deferred payment loan of up to $30,000 for home renovations. The loan has no monthly payments. It also does not come due for repayment until the owner sells or transfers ownership, or undertakes a cash-out refinance of the home.


To qualify for the loan, you need to be approved for an Additional Dwelling Unit permit. Your household income also needs to be at or below 135 percent of the Area Median Income. If your income is between 120 percent and 135 percent of the Area Median Income, you will have to provide a dollar-for-dollar match of the loan amount.

For more information, and to apply, visit the how-to webpage below:

Apply for Pilot Program Loan

The Home Modification Loan Program is a Massachusetts Rehabilitation Commission program. The program helps homeowners and small landlords fund updates to keep disabled or elderly family members in their own homes and communities.

How the loan works

The loan can be used to create additional living space and accessory dwelling units for persons with disabilities. Homeowners who are income-eligible may borrow up to $50,000 — inclusive of all costs — in a no-interest, deferred payment loan.

For more information, and to apply, visit the Home Modification Loan Program website:

Home Modification Loan Program


ADU pre-existing unit and carve out unit

ADU basement and attic locations

There are many ways to design and build your additional dwelling unit. We want to highlight some of the most important design tips and strategies in this toolkit. You can always choose to hire a planner, architect, or contractor to help you at any stage of the process. Our goal is to make this design process accessible to all homeowners through some general advice and guidance.

Building Code Requirements Basics

Since an additional dwelling unit is classified as an independent unit, it must be inspected as such. A unit should comply with all building and sanitary codes. Learn more about Boston’s Housing Code.

Below are some important code and other design considerations for additional dwelling units. There must be:

  • a full unit, which includes a bathroom and kitchen
  • two means of egress, which are ways for people to exit the building
  • water and electricity shutoff valves accessible to all units
  • compliant ceiling height, especially for basement and attic units, and
  • a sprinkler added in the new unit if you have 2- or 3-family home.

The unit cannot involve any bump out, extension, or construction to the existing envelope of the structure that results in the addition of gross floor area. Exterior work is allowed as long as the interior building square footage stays the same.

We will discuss all code and design considerations at your preliminary review.

Common questions

What are additional dwelling units?

They are a new type of residential unit that allow owner-occupants to carve out space in their homes for a smaller, independent unit.

Why is the City starting this pilot program?

Additional dwelling units will increase affordable housing options in the City. We want to create safer living arrangements and support multigenerational family arrangements. Our goal is to provide more chances for homeowners to age in place and stay in their homes. These units offer an opportunity to use existing infrastructure to achieve the City’s housing goals.

How do I apply for the pilot program?

There are four steps to apply for the Additional Dwelling Unit pilot program:

  1. Plan for your unit
  2. Complete a preliminary application
  3. Go to a preliminary review
  4. Complete an Inspectional Services permit

Our how-to guide on additional dwelling unit permits has more information.

How do I know if I’m eligible for the pilot?

You must be a homeowner of a one-, two-, or three-family home in East Boston, Jamaica Plain, or Mattapan. You also need to be an owner-occupant, meaning that you live on the property.

If I create a unit, what happens when the pilot ends?

Additional dwelling units permitted before the end of the pilot will be able to stay. If the pilot ends after the 18-month period, the City won’t permit any new additional dwelling units.

What if I sell my home?

If the new owner would like to use the additional dwelling unit as a rental unit, they will need to live on the property. They also must continue to register the unit with the rental registry.

What if there is already an unpermitted additional unit in my home?

We want to help homeowners bring existing units up to code. If you are eligible for the pilot program, and your current unit can meet all of our criteria, you can apply to have it permitted as a rental unit.

What do I do if my property is in the FEMA Flood Zone?

You must be able to show that the lowest elevation of the building (the "Top of Bottom Floor" on your elevation certificate) is above the Base Flood Elevation (BFE) to be eligible for the ADU program. An Elevation Certificate will show the BFE. You may want to check your mortgage documents for this information.  If you need to obtain an Elevation Certificate for your property, Elevation Certificates are prepared and certified by a Licensed Land Surveyor, Registered Professional Engineer or Registered Architect who is authorized by state or local law to certify elevation information. There is a useful FEMA website that explains (1) what an Elevation Certificate is and (2) how to get one for your property. Once you obtain an Elevation Certificate for your property, please include it with your application or send a copy to We will review and decide if your property is eligible for an ADU. 

Who can I talk to if I have additional questions?

Contact the Housing Innovation Lab at or 617-635-0259.