Weld

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.

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.

• Housing Opportunity Program (HOP)
• MaineHousing First Home Loan Program
• MaineHousing Home Energy Loan Program

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.