Bridgewater · Plymouth County

Can you build an ADU in Bridgewater?

Bridgewater's zoning ordinance, revised 22 May 2025, handles ADUs at Section 4.5. Most of it tracks the state floor. Two clauses do not, and one of them hands a subjective design test to a single official on a use that is otherwise allowed by right.

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 Bridgewater adds on top

Rule	In Bridgewater
Where allowed	Single-family dwellings only, and one ADU per lot, under Section 4.5(3)
Forms permitted	Conversion, attached or detached
Maximum size	Half the principal dwelling's gross floor area or 900 sq ft, whichever is smaller, with a separate entrance meeting state egress requirements
Dimensional rules	Section 4.1 general regulations and the Table of Dimensional Requirements that applies to the principal building in that district
Short-term rental	Prohibited, per Section 4.5(4), citing M.G.L. Chapter 64G Section 1
Separate sale	Barred. The principal dwelling and the ADU cannot be sold, conveyed or transferred apart from each other, under Section 4.5(5)
Before the building permit	A floor plan showing existing and proposed changes to both the interior and the exterior
The exterior test	The exterior must, in the opinion of the Building Inspector, retain the characteristics of a single family residence
Also applies	The Wetlands Protection Act at G.L. c.131 s.40, the state building code at 780 CMR, and Title 5 at 310 CMR 15

Section 4.5(6) is the clause to read before you draw anything. On a use the state makes available by right, Bridgewater still requires the exterior to keep the characteristics of a single family residence in the Building Inspector's opinion, which is a judgement rather than a measurement. A detached unit at the back of a lot can meet every dimensional rule and still meet an objection on that ground. Ask the Building Department how they have been reading it before you pay an architect. The ordinance also points at Title 5 and the Wetlands Protection Act, which on Bridgewater's septic-served outlying parcels and near the Town River is more than a formality.

Questions people ask

Can I build an ADU on a two-family in Bridgewater?

No. Section 4.5(3) limits accessory dwelling units to single family dwellings, and to one ADU per lot.

How big can a Bridgewater ADU be?

No larger than half the gross floor area of the principal dwelling or 900 square feet, whichever is smaller. It must also have a separate entrance meeting the state building code requirements for safe egress.

Can I sell the ADU separately in Bridgewater?

No. Section 4.5(5) bars the principal dwelling and the accessory dwelling unit from being sold, conveyed or transferred separately from one another.

Does Bridgewater have design requirements for an ADU?

Yes, and they are discretionary. Section 4.5(6) requires a floor plan showing interior and exterior changes before a building permit issues, and states that the exterior must, in the opinion of the Building Inspector, retain the characteristics of a single family residence.