5 county-level rules, plus city-specific rules for 1 city in Plymouth County, Massachusetts.
Verified from official government sources
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.
MGL c.40A §3
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
A small shed skips the building permit everywhere in Plymouth County. The state code exempts a one-story detached storage shed of 200 square feet or less, so a backyard shed in Plymouth or Brockton needs no building permit.
780 CMR 51.00 R105.2
One-story detached accessory structures used as tool and storage sheds, playhouses, and similar uses provided that the floor area does not exceed 200 ft2
Turning a garage into living space is permitted work under 780 CMR in every Plymouth County town. It is a change of use, so the building department reviews egress, ceiling height, insulation, and smoke and carbon monoxide alarms before signing off.
A carport is a roofed structure, so it takes a building permit in every Plymouth County town under 780 CMR. The town, never the county, reviews it, and local zoning setbacks control how close it can sit to the lot line.
A tiny home's rules in Plymouth County turn on its foundation. Built on a permanent foundation at 900 square feet or less, it now qualifies as a by-right accessory dwelling unit; on wheels, it is an RV that zoning does not treat as a permanent home.
MGL c.40A §3
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
1 cities in Plymouth County have their own accessory structures rules. Each link goes to that city's dedicated page with code citations.
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