Most of the State’s zoning laws are found in Chapter 40a of the Massachusetts General Laws. This Chapter, first and foremost, gives cities and towns the authority to adopt zoning ordinances and by-laws. It also establishes, among other items: 

1. What local zoning cannot regulate (Section 3);
2. Procedures cities and towns must follow when adopting zoning ordinances and by-laws (Section 5); 
3. How those ordinances and by-laws are to be enforced (Section 7); and
4. Processes for granting variances and special permits (Sections 9-11b).

The recently passed MBTA-Communities Act is also included under this chapter in Section 3A, which is why you might have heard it referred to as “3A.” The full text of Chapter 40a can be found on the Massachusetts Legislature’s website. 

Yes, chapters 40b, 40r, and 40y all have sections that impact different aspects of state zoning law. Sections 20-23 of Chapter 40b are the result of the State’s landmark “Anti-Snob Zoning Act” and establish the process through which a developer can obtain a comprehensive permit to build income-restricted housing. Chapters 40r and 40y provide funds to cities and towns that adopt “smart growth” and “starter home” zoning districts, respectively.

The Affordable Homes Act signed into law by Governor Healey this past legislative session included a provision that “legalized” ADUs in Massachusetts. This was done by amending Section 3 – the section listing the items local zoning cannot regulate – of Chapter 40a to include Accessory Dwelling Units in single-family zoned districts. In practice, this means that any zoning local ordinance or by-law that does not allow for by-right permitting of ADUs as defined in the statute, is void and unenforceable.

Oddly enough, Boston has always been exempted from state zoning law under Chapter 40a. As a result, any law that amends Chapter 40a does not impact Boston’s zoning rules, which is why the new ADU law passed in the Affordable Homes Act does not apply to Boston.