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Can you build an ADU (Accessory Dwelling Unit) on your property?

Since February 2025, Massachusetts law requires 350 cities and towns — every one except Boston, which writes its own zoning code — to allow one accessory dwelling unit by right in any district that allows single-family homes. A few questions and we'll tell you what the state guarantees you — including the square footage you're actually allowed, which is usually not the 900 you've read about.

One thing the state law did not do: erase your town's role. Local bylaws still apply — dimensional rules like setbacks, height, and lot coverage — and a building permit is still required. By right means no special permit and no discretionary hearing, not “no rules.”

Only used to word the answer. Nothing is looked up and nothing is stored.

Boston plays by a different rulebook

The 2025 state ADU law works through Chapter 40A, the state zoning act — and for historical reasons Chapter 40A has never applied to Boston. Boston writes its own zoning code and runs its own ADU program, with its own rules about who qualifies, what size is allowed and what approvals you need. Nothing this screener checks would tell you the truth about a Boston address.

If your property is in Boston, start with the City's own ADU information rather than the state rules. If it's in a town that borders Boston — Brookline, Newton, Milton, Quincy, Everett and the rest are all ordinary Chapter 40A municipalities — type that town instead and the screener works normally.

What kind of home is on the lot?

The state protection follows the zoning district, not the kind of building. Most homes in Massachusetts sit in a district that qualifies — this answer just changes what else we have to tell you.

An ADU has to be accessory to something

The state rule defines an accessory dwelling unit as a unit on the same lot as a principal dwelling — a main house that already exists. On vacant land there is nothing for it to be accessory to, so the ADU route doesn't open until the main house is built or approved. Build the house first, and the ADU question becomes a live one.

If you're planning both at once, that's a real question and the order matters: email us about your property and we'll tell you honestly whether it's worth pursuing.

How many separate homes are on the lot right now?

Count whole homes — the main house, a second house, each side of a two-family. Don't count a unit here if it's an in-law apartment; that's the next question.

Is there already an accessory apartment on the lot?

An in-law apartment or ADU: smaller than the main house, with its own kitchen, bathroom and entrance. This is a different question from the one above — a second full house, or the second unit of a two-family, is not an accessory apartment and doesn't use up your ADU.

A rough number is fine — your listing, tax bill, or assessor's card will have one. This is the number that sets your size limit, so leaving it blank means we can't give you one. Don't count the garage.

How many bedrooms does the house have now?

Bedrooms, not rooms. If you're on a septic tank this is the number that decides whether your apartment can have a bedroom at all — the two get counted together against what your system was designed for.

Where would the ADU go?
Would it have its own kitchen?

This is the line between an apartment and a bedroom suite, and the two follow completely different rules.

Town sewer, or a septic tank?

If you've never had a tank pumped, you're almost certainly on town sewer. This is the item that most often decides an ADU project — but a screen can't resolve it.

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Ask about a feasibility report

Your answers above come with it, so there's nothing to repeat. We'll come back to you with what the report would cover for your address and what it costs.

No payment now — this is a question, not an order.

We use this to answer you about this property, and nothing else. We never sell or share your information — no mailing list, no data brokers, no advertising trackers, no cookies on this page. Privacy & security. If your enquiry becomes an order, the Service Terms are the agreement between us — what you get, what you don't, and how refunds work.

What this is: a plain-English reading of Massachusetts state law — M.G.L. c. 40A §§ 1A and 3, in force 2 February 2025, and the regulation 760 CMR 71.00, effective 31 January 2025 — applied to what you told us. It is the same for every lot in your town, because the state floor is the same everywhere. What it is not: legal advice, a zoning determination, or a reading of your town's own bylaw. Your town may be more generous than the state floor; on the things the state fixed, it cannot be stricter. Nothing here is specific to your address.

Your privacy. This screener runs entirely inside your own browser — nothing you type above is sent anywhere unless you choose to contact us. This site sets no cookies and no tracking of any kind, and Bircch never sells or shares what you tell us. Read the full policy.

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