Does Plymouth County, MA have its own adu rules ordinance?

No. Plymouth County, MA does not appear to have a local adu rules ordinance, Massachusetts state law applies instead. The rules summarized on this page come from Massachusetts General Laws.

Key Facts Ordinance Text Full Breakdown Violations FAQ Sources More in Plymouth County

Plymouth County, MA Accessory Structures: ADU Rules (2026)

Some Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified September 2026

ADU rules in Plymouth County, MA, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

Status: By-right in single-family zones
Max Size: 900 sq ft or half
Governing Law: MGL c.40A §3
Effective: February 2, 2025

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Massachusetts under recent ADU streamlining laws. The Plymouth County, MA rules below cover local size, height, and setback requirements.

Summary

Since February 2025 an accessory dwelling unit up to 900 square feet is allowed by right in every single-family zone across Plymouth County. State law, not town discretion, made it: no special permit can be required to build one.

City-specific rules exist: Brockton has its own adu rules rules that differ from Plymouth County's county-level regulations. If you live in Brockton, check the city-specific page instead.

No zoning ordinance or by-law shall prohibit, unreasonably restrict or require a special permit or other discretionary zoning approval for the use of land or structures for a single accessory dwelling unit, or the rental thereof, in a single-family residential zoning district

Source: Massachusetts General LawsView official code

Full Breakdown

The 2024 Affordable Homes Act amended MGL c.40A §3 so that no zoning bylaw may prohibit, unreasonably restrict, or require a special permit for a single accessory dwelling unit in a single-family residential district. Effective February 2, 2025, this binds Brockton, Plymouth, and every South Shore town. An ADU is a self-contained unit no larger than 900 square feet or half the principal dwelling's gross floor area, whichever is smaller, under §1A. The town still issues the building permit and applies setbacks and the state building code, but it cannot zone the unit out or demand owner-occupancy.

Violations & Fines

A town bylaw that bans an ADU, caps it below the state size, or forces a special permit is unenforceable against a conforming unit. Building without the town building permit still draws a stop-work order.

Frequently Asked Questions

Can my town make me get a special permit for an ADU?

No. MGL c.40A §3 bars any special permit or discretionary approval for one ADU in a single-family zone. A building permit still applies.

How big can an ADU be?

Up to 900 square feet, or half the main house's gross floor area, whichever is smaller, under MGL c.40A §1A.

Sources & Official References

[1]Massachusetts General Laws

Other rules in Plymouth County

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All Plymouth County rules

How Plymouth County compares: Easiest Cities to Build an ADU·Compare Plymouth County to another location·View the Massachusetts accessory structures overview

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ADU Rules in Cities Across Plymouth County

Brockton, MA