ADU Size Limit: A Massachusetts Homeowner Guide
A protected-use ADU in Massachusetts may be up to 900 square feet or 50% of the principal dwelling's gross floor area, whichever is smaller, under the statewide rule effective January 31, 2025. A 1,400-square-foot main house, for example, may limit the ADU to 700 square feet, even though the statutory ceiling is 900 square feet. […]
Massachusetts ADU Laws: Complete Guide for Homeowners
In Arlington, Massachusetts, one ADU has been allowed by right statewide in single-family zoning districts since February 2, 2025. For most Greater Boston projects, the unit is capped at the smaller of 900 square feet or half the gross floor area of the principal dwelling, so the new law opens the door without removing the […]