Maine

Maine passed statewide ADU legislation in 2023 that requires municipalities to allow at least one accessory dwelling unit on any lot where a single-family home is permitted. The law is part of the state's effort to address a severe housing shortage. ADU Pass helps Maine homeowners navigate the permitting process under this new framework.

535 ZIP codes
16 Counties
420 Cities

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State ADU details

State ADU law

Maine enacted statewide ADU preemption with LD 2003 (Public Law 2021, Chapter 672), signed by Governor Janet Mills on 2022-04-27 and effective 2022-07-27 (most provisions effective 2023-07-01; municipal compliance deadline 2024-01-01 for council-style and 2024-07-01 for town-meeting-style). LD 2003 is codified principally at 30-A MRSA §4364-B. The law requires every Maine municipality to allow at least one ADU on every lot with a single-family home, attached or detached. LD 1706 (2023) clarified the framework. A 2025 amendment removed owner-occupancy requirements, making Maine's ADU regime among the most permissive in New England. Maine also eliminated single-family-only zoning statewide (allowing 2-4 units in qualifying districts) and reduced regulatory barriers to multi-family housing as part of the same package. Some municipalities have challenged the law; the Maine Department of Economic and Community Development (DECD) issues compliance guidance.

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State financing programs

Maine has an active state-level ADU financing framework. The Maine State Housing Authority (MaineHousing) administers low-interest mortgages, down-payment assistance, and a specific Housing Opportunity Program that funds municipal-level ADU programs. The Department of Economic and Community Development (DECD) administers the Housing Opportunity Program, which can grant up to $500,000 per municipality to fund local ADU incentive programs. Eligible homeowners are typically those with incomes at or below 120% of Area Median Income. The City of Auburn's grant program (one of the largest implementations) provides up to 15% of construction costs or $30,000 per ADU.

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State insurance regimes

Maine does not currently operate an active FAIR Plan or wind pool. Maine has the statutory means to create a FAIR Plan if a particular type of insurance becomes unavailable, but no such plan is currently active. Property insurance in Maine is regulated by the Maine Bureau of Insurance under Title 24-A MRSA. Coastal Maine properties (Hancock, Knox, Lincoln, Sagadahoc, Cumberland, York counties along the Atlantic coast) face hurricane and wind exposure; many policies in coastal areas carry hurricane or wind/hail deductibles of 1-10% of dwelling value, often triggered for properties within 1,000 feet to 2 miles of the coast. ADUs are typically covered as accessory structures under standard homeowner policies (often at ~10% of dwelling coverage) or require a dwelling-fire or landlord endorsement when rented. Climate change is increasing premium pressure statewide, particularly in coastal and flood-zone properties.

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State housing programs

Maine's primary state-level ADU program framework is the LD 2003 / 30-A MRSA §4364-B preemption regime plus the DECD Housing Opportunity Program (HOP), which funds municipal ADU initiatives. Maine does not operate a statewide pre-approved ADU plan catalog or a statewide impact-fee waiver, but the LD 2003 floor functionally limits what fees municipalities may impose. The MaineHousing GrowSmart and 'Maine ADU Guide' (https://maineaduguide.org) provide educational resources and design templates statewide.

  • LD 2003 / 30-A MRSA §4364-B Statewide ADU Floor — Every municipality must allow at least one ADU per single-family lot. No owner-occupancy requirement (per 2025 amendment). Municipalities cannot prohibit ADUs.
  • Housing Opportunity Program (HOP) ADU Grants — DECD-funded grants of up to $500,000 to municipalities to support ADU production, often passed through to homeowners (≤120% AMI) for direct construction support.
  • Maine ADU Guide — Educational resource portal funded by MaineHousing and DECD providing design guidance, financing information, and municipal-compliance support for Maine ADUs.
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Known state issues (2)

  • policy-review (since 2023-07-01) — Where local code conflicts with the state floor, the state floor controls. Practitioners should confirm both state-floor and local-implementation status before relying on local code language alone. (source)
  • other (since 2023-01-01) — Coastal-county ADU pro forma should assume elevated premium and hurricane-deductible cost; confirm carrier appetite before construction. (source)
Federal (United States) — ADU-relevant rules and programs

Federal ADU law

The United States has no federal statute that directly regulates accessory dwelling unit entitlement or design. Land-use authority over ADUs resides with states and local governments under the traditional police power. Federal engagement is limited to financing (Fannie/Freddie/FHA/VA/USDA), flood insurance (FEMA/NFIP), and discretionary housing programs (HUD), which are recorded in sibling sections of this file.

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Federal financing programs

Federal housing-finance agencies and GSEs set nationwide underwriting rules that govern whether an ADU can be financed, appraised, and counted toward mortgage qualifying income. The relevant actors are Fannie Mae, Freddie Mac, FHA (HUD), VA, and USDA Rural Development.

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Federal tax credits

There is no ADU-specific federal tax credit. ADUs may incidentally qualify for existing federal energy-efficiency and clean-energy tax credits when the ADU construction includes qualifying measures.

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Federal housing programs

HUD administers several discretionary programs that can fund ADU-related activity at the grantee's election, but none is an ADU-specific program.

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