Can I build an ADU in Massachusetts without a special permit?

Yes. Since February 2, 2025, the state's Affordable Homes Act requires municipalities to allow at least one accessory dwelling unit under 900 square feet by-right on any lot zoned for a single-family home. Local occupancy restrictions on who may live in the ADU are prohibited, and towns cannot impose parking requirements beyond what the state law allows.

What is the MBTA Communities Act and does it apply to my town?

It's Section 3A of Chapter 40A, which requires the 177 cities and towns served by MBTA transit to zone at least one district for multifamily housing as-of-right at a minimum of 15 units per acre. A municipality that hasn't adopted a compliant district risks losing eligibility for certain state infrastructure and housing grant programs.

Does Massachusetts have countywide zoning I need to check?

No. County government has been abolished or is largely vestigial across Massachusetts, so zoning authority sits entirely with the state's 351 individual cities and towns. You need to review each municipality's own Chapter 40A zoning ordinance or bylaw directly.

How can I override restrictive local zoning for an affordable housing project?

Chapter 40B's Comprehensive Permit process lets a developer of income-restricted housing file a single application with the local Zoning Board of Appeals that can supersede the municipality's own zoning bylaws, in any city or town where less than 10% of the year-round housing stock is subsidized affordable housing.

Massachusetts · state zoning reference · Waitlist open

Massachusetts zoning: how it works and what you can build

Massachusetts zoning is exercised entirely by its 351 cities and towns under home rule, but the state has increasingly forced local upzoning through the MBTA Communities Act and a decades-old affordable-housing override, making state-level pressure as important to track as any local ordinance.

How zoning works in Massachusetts

Massachusetts municipalities derive their zoning authority from the 1966 Home Rule Amendment (Article 89 of the Massachusetts Constitution), which ended strict Dillon's Rule for local government, and from Massachusetts General Laws Chapter 40A, known as "The Zoning Act," the general enabling statute for municipal zoning ordinances and bylaws. Critically, the Legislature has retained what courts describe as "supreme power in zoning matters," meaning Beacon Hill can and does override local zoning outcomes it finds insufficient. There is no county layer of zoning in Massachusetts — county government has been abolished or is vestigial across most of the state — so all zoning decisions run through one of the 351 individual city or town governments, each with its own zoning map, board of appeals, and planning board.

The most consequential recent state action is the MBTA Communities Act (Chapter 40A, Section 3A), enacted in 2021, which requires each of the 177 cities and towns served by MBTA transit to zone at least one district of "reasonable size" for multi-family housing as-of-right at a minimum gross density of 15 units per acre, with no age restrictions. Noncompliant communities risk losing eligibility for several state grant programs, and as of early 2026 the large majority of MBTA communities have adopted compliant districts. Layered on top of that is Chapter 40B, the state's long-standing Comprehensive Permit Act, which lets developers of income-restricted housing seek a single consolidated permit from the local Zoning Board of Appeals that can override local zoning bylaws in any municipality where less than 10% of the housing stock is subsidized affordable housing — a tool used heavily in the state's more restrictively-zoned suburbs.

Most recently, the 2024 Affordable Homes Act made accessory dwelling units legal by-right statewide effective February 2025: ADUs under 900 square feet must now be permitted as-of-right in any district that allows single-family homes, occupancy restrictions on who may live in them are prohibited, and municipalities' ability to impose parking minimums is capped. A handful of municipalities have gone further on their own — Cambridge eliminated single-family-only zoning citywide in February 2025, allowing four-story multifamily buildings as-of-right (up to six stories for projects with inclusionary affordable units on lots over 5,000 square feet) with no parking minimums. For developers, the practical takeaway is that Massachusetts zoning review has to happen twice: once against the local zoning ordinance or bylaw, and once against whichever state override (40B, 40A §3A, or the ADU law) might unlock density the local map doesn't show.

Who holds the zoning power

Land-use authority in Massachusetts is delegated by statute, not assumed — these are the acts a zoning ordinance in Massachusetts has to trace back to.

The Zoning Act Massachusetts General Laws Chapter 40A: General enabling statute for municipal zoning ordinances and bylaws
MBTA Communities Act Massachusetts General Laws Chapter 40A, Section 3A: Requires 177 transit-served municipalities to zone at least one multifamily district as-of-right at 15+ units/acre
Comprehensive Permit Act Massachusetts General Laws Chapter 40B: Lets affordable-housing developers seek a single override permit in municipalities below 10% subsidized housing

Major cities and their codes

The enabling act sets the ceiling; the municipal code is what a project is actually reviewed against. The 7 largest Massachusetts jurisdictions and the codes they administer:

Massachusetts — municipal zoning codes
City	Zoning code
Boston	Boston Zoning Code, with large projects subject to Article 80 development review Boston Planning Department runs a formal Article 80 design and impact review for larger projects on top of base zoning
Cambridge	Cambridge Zoning Ordinance Eliminated single-family-only zoning citywide in February 2025, allowing four- to six-story multifamily as-of-right
Worcester	City of Worcester Zoning Ordinance The state's second-largest city; still substantially single- and two-family zoned outside downtown
Springfield	City of Springfield Zoning Ordinance An MBTA community subject to the Section 3A multifamily-district mandate
Lowell	Lowell Zoning Ordinance Former mill city with adaptive-reuse overlay districts feeding an active redevelopment pipeline
Quincy	Quincy Zoning Ordinance Downtown Quincy transit-oriented overlay has driven high-rise residential redevelopment near the MBTA Red Line
New Bedford	New Bedford Zoning Ordinance Waterfront and historic-mill districts carry separate overlay standards from the base residential zones

Recent reforms

State-level changes override or preempt what a local ordinance says — these are the Massachusetts reforms that move the numbers on a real site.

2025 Cambridge eliminates single-family zoning citywide First Massachusetts city to allow multifamily housing as-of-right in every residential district
2024 Affordable Homes Act — statewide ADU law Made ADUs under 900 sq ft legal by-right statewide in single-family districts, effective February 2025
2021 MBTA Communities Act (Ch. 40A §3A) Requires 177 transit-served municipalities to zone a multifamily district as-of-right at 15+ units/acre

Parcel & GIS data

MassGIS (the state's Bureau of Geographic Information) publishes a statewide Standardized Assessors' Parcels dataset compiled from municipal assessor records, giving relatively consistent parcel coverage despite zoning itself being set locally.

Parcel-level feasibility in Massachusetts waits on that data being ingested and the ordinances encoded — the waitlist below is what sets the order.

Zoning by city

The statute sets who may zone; the city's own code sets what you can build. One guide per Massachusetts city below, explaining the district codes that appear on its zoning map — 86 district codes across Massachusetts so far.

Massachusetts zoning — common questions

Can I build an ADU in Massachusetts without a special permit?: Yes. Since February 2, 2025, the state's Affordable Homes Act requires municipalities to allow at least one accessory dwelling unit under 900 square feet by-right on any lot zoned for a single-family home. Local occupancy restrictions on who may live in the ADU are prohibited, and towns cannot impose parking requirements beyond what the state law allows.
What is the MBTA Communities Act and does it apply to my town?: It's Section 3A of Chapter 40A, which requires the 177 cities and towns served by MBTA transit to zone at least one district for multifamily housing as-of-right at a minimum of 15 units per acre. A municipality that hasn't adopted a compliant district risks losing eligibility for certain state infrastructure and housing grant programs.
Does Massachusetts have countywide zoning I need to check?: No. County government has been abolished or is largely vestigial across Massachusetts, so zoning authority sits entirely with the state's 351 individual cities and towns. You need to review each municipality's own Chapter 40A zoning ordinance or bylaw directly.
How can I override restrictive local zoning for an affordable housing project?: Chapter 40B's Comprehensive Permit process lets a developer of income-restricted housing file a single application with the local Zoning Board of Appeals that can supersede the municipality's own zoning bylaws, in any city or town where less than 10% of the year-round housing stock is subsidized affordable housing.

Working in Massachusetts? Get on the list.

The parcel layer lands in the order demand does. Illinois went first because that's where the deals were; the next state is decided by who tells us what they're trying to underwrite. Tell us where you're building and what you wanted to run — you'll hear from us when Massachusetts opens, and sooner if we need a test parcel.

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Want to see the finished shape of this work? Illinois is live at parcel level — Illinois zoning and the 53-district Chicago reference.

Massachusetts zoning summaries on this page are provided for information, not legal advice. Confirm every project against the current adopted code for the jurisdiction and the statute as amended.