Boston uses a local ADU program and zoning screen. The City’s Research your ADU Options page says baseline eligibility requires an owner-occupant of a one-, two-, or three-family home within Boston. The page says condominiums and LLCs are not eligible for this program. Confirm the property’s legal form and owner status with the City.
Check the project form
Boston zoning currently allows one internal ADU in an owner-occupied one-, two-, or three-family home throughout the city, using the existing building footprint without adding floor area. An attached addition or a detached ADU may require a variance from the Zoning Board of Appeal; the City’s guidance does not promise that a variance will be granted.
Check whether the Mattapan exception applies
The City identifies a geographic exception for parcels inside both the Greater Mattapan Neighborhood Zoning District and the PLAN: Mattapan study area. In that area, the City says all listed ADU types may be built without special approval. An eligible owner-occupant may add up to one non-detached and one detached ADU, subject to the maximum units allowed in the parcel’s subdistrict. The City’s guidance directs Mattapan homeowners to verify the Greater Mattapan district and R1 or R2 subdistrict in the zoning viewer.
Check the parcel in the City’s zoning viewer and compare the result with the current zoning text. Flood-zone siting, dimensional limits, and building permits remain separate checks. The citywide internal-unit rule and Mattapan exception are screening routes, not a property-specific eligibility determination.