Easier Than Ever to Build
Massachusetts has just made one of the most significant zoning changes in recent years, making it easier for homeowners to build Accessory Dwelling Units (ADUs)—commonly known as in-law apartments or granny flats.
As of February 2, 2025, a new state law allows ADUs by right in single-family residential zoning districts across Massachusetts (excluding Boston). This means that most homeowners no longer need to go through a special permit process, reducing delays and making ADU construction more accessible. The state estimates this change could add 8,000 to 10,000 new housing units, helping to address Massachusetts’ ongoing housing shortage.
Key ADU Provisions Under the New Law
If you’re considering building an ADU, here’s what you need to know:
Size Limits: The ADU cannot exceed 50% of the primary home’s square footage or 900 square feet, whichever is smaller.
Types of ADUs Allowed: Homeowners can build detached ADUs, convert an existing basement or attic, or add an extension to their home.
Zoning Restrictions: The new law only applies to single-family residential zoning districts.
Separate Entrance Required: Every ADU must have its own exterior entrance, separate from the main home.
Municipal Regulations Still Apply
While cities and towns cannot ban ADUs outright, they can impose certain restrictions, including:
✔ Site plan review (under a streamlined process)
✔ Setback requirements to maintain neighborhood character
✔ Height limitations
✔ Septic system requirements (for homes not on public sewer)
✔ Short-term rental restrictions to prevent ADUs from becoming Airbnb-style rentals
What Municipalities Cannot Do
🚫 Require a family relationship between the homeowner and ADU occupant
🚫 Mandate off-street parking for ADUs located within ½ mile of a transit station
🚫 Impose special permit requirements or discretionary zoning approvals
🚫 Create unreasonable restrictions that make it difficult to build an ADU
This policy shift provides homeowners with new opportunities—whether to create rental income, house aging parents, or provide affordable housing options.
Want to Learn More?
For additional details and municipal guidance, visit the official state website:
🔗 Massachusetts ADU Information: https://www.mass.gov/info-details/accessory-dwelling-units
If you’re considering adding an ADU to your property in Greater Boston, the South Shore, or MetroWest Reach Out to me
