Big News for Housing in Maine: LD 1829 Signed into Law!
Backyard ADU’s 525SF S-Line ADU design path
We’re celebrating a huge win for housing in Maine—LD 1829 was officially signed into law by Governor Janet Mills! This legislation is a powerful follow-up to the landmark 2022 law, LD 2003, which legalized accessory dwelling units (ADUs) statewide and began the long-overdue process of zoning reform across Maine.
LD 1829 builds on that progress with clearer, stronger rules that make it easier to build ADUs and multifamily housing, while reducing red tape for homeowners, builders, and municipalities alike.
Here’s what’s in the new law—and why it matters:
No More Sprinkler Requirement for Most ADUs
Municipalities can no longer require fire sprinklers for ADUs unless the structure contains three or more total units (including the ADU). This is a game-changer, especially in cities like Portland, where sprinkler mandates were making ADUs financially unfeasible. It’s a win for affordability, flexibility, and common sense.
More Homes Allowed on Every Residential Lot
Municipalities must now allow:
At least three dwelling units on any lot where residential use is permitted
Up to four units in designated growth areas or on lots served by both water and sewer
This change opens the door for small-scale infill development, which can add gentle density while preserving neighborhood character.
Smaller Lot Sizes in Urbanized Areas
Minimum lot sizes in areas with water and sewer are now capped at 5,000 square feet, removing an outdated barrier to building more homes in walkable, connected places.
ADUs Are No Longer Limited to Single-Family Lots
LD 1829 clarifies that ADUs can also be added to lots with existing multifamily housing, not just single-family homes. This broadens the scope of where ADUs can be built and maximizes their potential as a tool for housing access.
Non-Conforming Lots Get a Fair Shot
Municipalities must allow ADUs on non-conforming lots, as long as the addition of the ADU doesn’t increase the existing nonconformity. This opens up many more lots for housing without impacting neighborhood standards.
Owner Occupancy No Longer Required
One of the most significant updates: ADUs must be allowed even if the owner doesn’t live on the property. This change invites more investment, supports rental opportunities, and gives property owners more flexibility in how they use and finance their land.
More Room for Affordable Housing
The bill also revises subdivision laws, increasing the threshold from three to five units before triggering subdivision review. This allows small-scale affordable housing developments to move forward with less delay and lower cost.
When Does the Law Go Into Effect?
LD 1829 becomes law 90 days after the close of the legislative session, which means late September 2025. Municipalities will need to update their ordinances.
At Backyard ADUs, we’re thrilled by this legislative victory. It’s a critical step forward for flexible, attainable, and sustainable housing across Maine. If you're a homeowner, builder, or policy advocate looking to understand how these changes affect your community—or your property—get in touch. We're here to help.
Liz Trice – Partnerships Director, Backyard ADUs
Liz Trice brings a strong background in community development, policy advocacy, and coalition-building to her role at Backyard ADUs. With a passion for housing innovation and local empowerment, she works to bridge the gap between municipalities, nonprofits, and private partners to advance sustainable ADU development across New England. Liz is committed to creating collaborative solutions that expand housing options while preserving community character. At Backyard ADUs, she leads strategic initiatives that help towns unlock funding, navigate zoning reform, and build programs that serve real people in real neighborhoods.