Braintree · Norfolk County

Can you build an ADU in Braintree?

Braintree adopted Section 135-618 by council vote on 16 September 2025, and it is the most useful ordinance on this list for anyone buying an older property. It lets a nonconforming accessory structure, an old garage set too close to the line, become a rentable unit without a variance.

What the state guarantees you

Since 2 February 2025 this applies in every Massachusetts community. A town may be more generous than this. It may not be less.

Rule	What it means
Allowed by right	One ADU in single-family zoning districts, statewideNo special permit and no public hearing for a protected-use ADU
Maximum size	900 sq ft, or 50% of the principal dwelling, whichever is smallerA town may allow larger. It cannot allow smaller
Owner occupancy	A town cannot require itSo you may rent both units, or live in the ADU and rent out the house
Parking	One space at most, and none at all within half a mile of transitA town cannot ask for more than this
Short-term rental	The state leaves this to each townAll six towns documented here ban it, and two of them ban it for the main house too
In force since	2 February 2025Any conflicting local zoning became unenforceable that day

What Braintree adds on top

Rule	In Braintree
Adopted	Voted 16 September 2025, order TCO 25-003, as Section 135-618
Where allowed	By right in RA, RB, RC, C123 and GB
Where not allowed	HB, C, OSC and BWLD
Maximum size	Half the principal dwelling's gross floor area, or 900 sq ft, whichever is smaller
How many	One ADU per lot may qualify as a Protected Use ADU
Nonconforming lots	An ADU may be built within, or on a lot with, a pre-existing nonconforming structure, provided it meets the Building Code, 760 CMR 71.00 and state law
Converting an old outbuilding	An existing accessory structure that is nonconforming as to setbacks, stories or height may be converted, so long as the conversion does not extend, expand or alter the nonconformity
Accessory setback	No accessory building within five feet of any lot line
Short-term rental	Prohibited, per MGL Chapter 64G Section 1
Dimensional rules	Section 135-701 and its notes

Section 135-618(C) is the part worth reading twice. Plenty of Braintree lots carry a detached garage or outbuilding that predates modern setbacks and could not be built there today. Ordinarily that structure is frozen: you may maintain it, not improve it. This ordinance opens a path to convert it into a dwelling, provided you do not make the nonconformity any worse. On the right property that is a second unit for the cost of a fit-out rather than a ground-up build. Braintree also defines a single-family residential zoning district broadly, reaching any district where single-family homes are allowed at all, including by special permit, which is why the use table extends into C123 and GB.

Questions people ask

Can I convert an old garage into an ADU in Braintree?

Yes, and this is unusual. Section 135-618(C) allows an existing accessory structure that is nonconforming as to setbacks, stories or building height to be converted to a Protected Use ADU, provided the conversion complies with Section 135-701 and does not extend, expand or alter the nonconformity in any way.

Which Braintree zoning districts allow an ADU?

Protected Use ADUs are permitted by right in RA, RB, RC, C123 and GB. They are not permitted in HB, C, OSC or BWLD.

How big can a Braintree ADU be?

No larger than half the gross floor area of the principal dwelling, or 900 square feet, whichever is smaller. Only one ADU on a lot may qualify as a Protected Use ADU.

Can I short-term rent a Braintree ADU?

No. Section 135-618(B)(4) prohibits using a Protected Use ADU as a short-term rental as defined in MGL Chapter 64G, Section 1.