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Zoning Guide

ADU Rules in Portland, Maine

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ADU Rules in Portland, Maine

Portland is the Cumberland County seat and Maine's largest city with a population of about 68,000. Known for its vibrant arts scene, Old Port cobblestone district, award-winning restaurants, Casco Bay views, and status as one of the best places to live in America, Portland has a severe housing shortage. The city has been actively expanding ADU allowances as part of its housing strategy. Maine has no statewide ADU preemption law — Portland's local zoning governs.

Portland ADU Policy

Portland has been a leader in New England on ADU policy, allowing ADUs broadly in residential zones to address housing affordability. The city has worked to simplify ADU approval.

Permitted ADU Types

Per Portland Zoning Ordinance:

  • Detached ADUs: Standalone structure in rear yard
  • Attached ADUs: Addition with separate entrance
  • Interior conversions: Basement, attic, or other conversion
  • Garage conversions: Converting existing garage to ADU

Portland has been generally permissive on ADU types — verify current specific standards.

Size Limits

Per Portland Zoning Ordinance:

  • ADU size limits apply per zone — verify current standards
  • Portland has been working to allow larger ADUs

Setbacks

Per Portland residential zone:

  • Rear: Minimum setback
  • Side: Minimum setback

Maine Shoreland Zoning

Properties within 250 feet of a Great Pond, river, stream, or coastal shoreline are subject to Maine's Shoreland Zoning Act (Title 38). Portland's coastal location means many properties may be in shoreland zones. Verify if your property is in a shoreland protection zone.

Historic Districts

Portland has the Old Port and several historic districts. Properties in historic districts require review by the Historic Preservation Board for exterior modifications.

Coastal Flood Zones

Parts of Portland's waterfront and peninsulas are in FEMA flood zones. Verify flood map status for coastal properties.

Permit Process

  1. Verify ADU eligibility: Portland Planning Division (broadly allowed)
  2. Check shoreland zoning: If near water bodies
  3. Historic review: If in a historic district
  4. Check flood zone status: If on the waterfront
  5. Submit plans: Portland Building Division
  6. Building permit and inspections
  7. CO: Required before occupancy

Contact

City of Portland Planning Division 389 Congress Street, Portland, ME 04101 Phone: (207) 874-8720 Website: portlandmaine.gov

Disclaimer: Maine has no statewide ADU law. Portland's ADU policies have been evolving and generally permissive. Verify current standards with the City of Portland before starting any project.

More about Portland Zoning

Sources

  1. Portland Zoning Administration·portlandmaine.gov·Accessed 2026-05-24·Direct link
  2. ReCode Portland - Official project site·recodeportland.me·Accessed 2026-05-24·Direct link
  3. Maine LD 2003 Guidance - Maine Department of Economic and Community Development·maine.gov·Accessed 2026-05-24·Direct link
  4. Portland Code of Ordinances (Municode)·library.municode.com·Accessed 2026-05-24·Direct link

FAQ

Are ADUs allowed in Portland, Maine?
Yes. Under statewide Maine LD 2003 (PL 2021, Ch. 672), Portland must allow at least one Accessory Dwelling Unit on any lot with a single-family dwelling. Portland's ReCode zoning ordinance (adopted November 4, 2024, effective December 4, 2024) sets local size, height, setback, and design standards for ADUs.
Does Maine have a statewide ADU law?
Yes. Maine enacted LD 2003 (PL 2021, Ch. 672) in April 2022, codified at 30-A MRSA Sec. 4364-B. It requires every municipality to allow at least one ADU on lots with a single-family dwelling, sets a minimum permitted ADU size of 190 sq ft, and allows up to four units in many residential zones. Compliance deadlines were January 1, 2024 (council-adopted ordinances) and July 1, 2024 (town meeting communities).
What is ReCode Portland?
ReCode is Portland's first comprehensive rewrite of its land-use code in more than 50 years. The City Council unanimously approved it on November 4, 2024 and it took effect December 4, 2024. It updates zone structure, dimensional standards, and use permissions, with the goal of allowing more housing in residential zones and concentrating density downtown and along key transit corridors.