ADU Rules in Plymouth, Massachusetts

Plymouth is the Plymouth County seat and the largest town by land area in Massachusetts, with a population of about 62,000 on Plymouth Bay. Known as "America's Hometown" — the landing site of the Pilgrims in 1620 — Plymouth has significant historic and tourist assets including Plymouth Rock, Plimoth Patuxent (formerly Plimoth Plantation), and Pilgrim Hall Museum. Plymouth is a town (not a city) and uses a Zoning Bylaw. Massachusetts enacted a statewide ADU law (Chapter 150, Acts of 2024) requiring ADUs by right in single-family zones.

Massachusetts Statewide ADU Law (2024)

Massachusetts Chapter 150, Acts of 2024 requires municipalities to allow ADUs by right in single-family residential zoning districts. Verify how Plymouth has implemented this law.

Plymouth Zoning Bylaw

The Town of Plymouth Zoning Bylaw governs all land use in Plymouth.

Permitted ADU Types

Per Massachusetts ADU law and Plymouth zoning (verify current standards):

• Basement and interior conversions
• Attached ADUs: With separate entrance
• Detached ADUs: Common given Plymouth's suburban and rural lot sizes

Size Limits

Per Massachusetts ADU law:

• ADU cannot exceed smaller of: primary dwelling or 900 square feet

Setbacks

Per Plymouth residential zone:

• Rear: Minimum setback
• Side: Minimum setback

Massachusetts Chapter 91 — Coastal Waterways

Plymouth has extensive coastline on Plymouth Bay, Plymouth Harbor, Priscilla Beach, and other coastal areas. Massachusetts Chapter 91 (Waterways Act) applies to tidelands. Properties near tidal waters require Chapter 91 review.

Coastal Flood Zones

Plymouth's extensive coastal areas have significant FEMA coastal flood zone exposure. Verify flood map status for all coastal properties. Coastal construction standards apply.

Massachusetts Wetlands Protection Act

Properties within 100 feet of wetlands, tidal areas, or coastal banks — and within 200 feet of rivers and streams — require Plymouth Conservation Commission review.

Historic Districts

Plymouth has historic downtown areas and nationally significant sites. Properties near the historic waterfront area may require review.

Permit Process

1. Verify zoning and state ADU law: Plymouth Planning Department
2. Chapter 91 review: If near Plymouth Bay or tidal areas
3. Conservation Commission review: If near coastal areas or wetlands
4. Check flood zone: For coastal properties
5. Historic review: If in a historic district
6. Submit plans: Plymouth Building Division
7. Building permit and inspections
8. CO: Required before occupancy

Contact

Town of Plymouth Planning Department 26 Court Street, Plymouth, MA 02360 Phone: (508) 747-1620 Website: plymouth-ma.gov/planning

Disclaimer: Massachusetts statewide ADU law (2024) applies. Coastal flood zones and Chapter 91 waterway restrictions apply to Plymouth's extensive coastline. Verify current standards before starting any project.