ADU Laws in Massachusetts (2026)
Massachusetts state ADU law details, key provisions, preemption status, and recent legislative changes for accessory dwelling units.
Law Name
Massachusetts Affordable Homes Act (Chapter 152, Acts of 2024) and MBTA Communities Act (Chapter 40A, Section 3A, 2021)
Effective Date
2021-01-14
Preempts Local Ordinances
Yes — state law overrides local restrictions
Has State Law
Yes
Key Provisions
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
Affordable Homes Act: Clarifies that ADUs can be rented (including to non-family members)
Legislative History
2021 — MBTA Communities Act (Chapter 40A, Section 3A)
Requires 177 MBTA communities to zone for multifamily housing by-right within one-half mile of transit stations. Creates minimum density requirements for transit-oriented districts. Non-compliant communities risk loss of state grant eligibility.
2024 — Affordable Homes Act (Chapter 152 of the Acts of 2024)
Comprehensive housing reform — requires municipalities of 10,000+ population to allow ADUs by-right in single-family zones. ADUs up to 900 sqft allowed without special permits. Eliminates owner-occupancy requirements for ADUs. Reduces parking requirements near transit. Effective January 1, 2025 for ADU provisions.
Official Sources
What Does Preemption Mean for Local Cities?
Because Massachusetts law preempts local ordinances, individual cities cannot impose restrictions stricter than the state standard. A city may still have additional administrative requirements, but cannot deny ADU applications that comply with state minimums.
Learn about Massachusettszoning preemption →Source: Massachusetts Affordable Homes Act (Chapter 152, Acts of 2024) and MBTA Communities Act (Chapter 40A, Section 3A, 2021). Last verified April 5, 2026. View source