Additional Dwelling Unit Program
The Additional Dwelling Unit Program allows owner occupants in the City of Boston to carve out a new space within their homes. They can create smaller, independent units, known as Additional Dwelling Units (ADUs) once the design has been approved. For those who qualify, we offer loans to build approved ADU designs.
To learn more about the ADU Pilot Program, including goals and lessons learned, visit the ADU Pilot Program page.
To stay up to date on the next steps of the ADU program — including ADU 2.0 for homeowners interested in turning existing exterior structures like carriage houses and underutilized garages into livable space — sign up for the email list.
You must meet these requirements to qualify for the Additional Dwelling Unit Program.
- Own a 1-, 2- or 3-family home within the city of Boston
- Live in that same home
- Plan to build your ADU in that same home
- Plan to build your ADU within the envelope of your home
- Plan to build your ADU above the Base Flood Elevation (BFE) if your home is in the FEMA Flood Zone, and you want to build a basement or first floor unit
Designing Your ADU
There are many ways to design and build your ADU. This section includes some important design tips and strategies. Our goal is to make this design process accessible to all homeowners through some general advice and guidance.
Building Code Requirements Basics
Below are some important code and other design considerations for ADUs. 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.
Find more Building Code requirements in the How to Apply for an ADU Permit section.
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.
To help with your planning, view the checklist.