State Preemption of Local Zoning in Massachusetts

What Is State Preemption?

State preemption occurs when a state law overrides local government ordinances in a specific area. In land use, preemption means a city or county cannot adopt zoning rules that are more restrictive than the state standard. If a city tries to prohibit something the state law permits, the state law wins.

Massachusetts actively uses preemption in housing law. The state has enacted legislation that prohibits local governments from blocking certain types of housing development — most notably accessory dwelling units (ADUs) and lot splits.

ADU Preemption

What local governments cannot restrict:

• ✓MBTA Communities Act (2021): Requires 177 municipalities served by the MBTA to zone for multifamily housing by-right near transit stations — minimum 15 units per acre in designated districts
• ✓MBTA Communities Act: Municipalities must have compliant zoning plans — non-compliance risks loss of state discretionary grants
• ✓Affordable Homes Act (Chapter 152, 2024): Requires municipalities of 10,000+ population to allow ADUs by-right in single-family zones — no discretionary permit required
• ✓Affordable Homes Act: ADUs of up to 900 sqft (or 50% of primary dwelling, whichever is greater) must be allowed by-right
• ✓Affordable Homes Act: Local municipalities cannot require owner-occupancy for ADUs
• ✓Affordable Homes Act: Local municipalities cannot require additional parking for ADUs within one-half mile of a transit station

How Preemption Affects Massachusetts Cities

State preemption applies to every incorporated city and unincorporated area in Massachusetts. Select a city below to see how state preemption interacts with local zoning rules.