Nonconforming Lots and Structures (Chapter 40A, Section 6)

A nonconforming lot, structure, or use is one that was lawful when it was created but doesn’t meet current zoning, usually because the bylaw changed afterward. Older neighborhoods are full of them: homes that sit closer to the street than today’s setback, or lots smaller than today’s minimum.

Section 6 of the Zoning Act (M.G.L. c. 40A) protects these “pre-existing nonconforming” situations and sets the rules for changing them.

Changing a nonconforming structure

Section 6 allows pre-existing nonconforming structures and uses to be changed, extended, or altered, with an important safeguard. In general, the change requires a finding by the board that it won’t be substantially more detrimental to the neighborhood than the existing nonconformity.

For single- and two-family homes, the process is often simpler. If a proposed change doesn’t increase the nonconforming nature of the structure, it may proceed without that finding. How “increase the nonconforming nature” is interpreted has been the subject of important court decisions, and local practice varies.

Protection for small lots

Section 6 also protects certain small lots for single- and two-family use when a community increases its minimum lot size or frontage. Lots that conformed when created, weren’t held in common ownership with adjoining land, and have at least 5,000 square feet of area and 50 feet of frontage can generally remain buildable. Separate protections apply to lots on recorded subdivision or ANR plans for a limited number of years.

The common-ownership condition is critical. Under the merger doctrine, adjoining substandard lots held by the same owner can be treated as one lot, and that can eliminate protection you might assume you have.

Why it matters

Section 6 is one of the most valuable and most misunderstood parts of Massachusetts zoning. An addition that looks impossible under today’s setbacks may be permitted. A lot that looks unbuildable may be protected. The opposite can also be true. The answer depends on the property’s history, its ownership, and the specific wording of the local bylaw.

General information, not legal advice. The history of a lot or structure often determines the answer.