Is it law?
Yes. It is enacted law, not a proposal. LD 1829 was signed June 20, 2025 as Public Law 2025, chapter 385. LD 2173 was signed April 16, 2026 as Public Law 2025, chapter 733, and took effect July 29, 2026. LD 2173 rewrote the rule and set one date for every town to apply it: July 1, 2027. LD 1829 as first passed would have applied a year earlier in some towns. LD 2173 removed that.
What the statute says
The rule is in 30-A M.R.S. §4364-A(1). The current text says that in any area where housing is allowed, the following are permitted uses:
- At least three dwelling units per lot, attached or detached, counting any ADUs.
- At least four dwelling units per lot if the lot is in a designated growth area or is served by both public water and public sewer.
"Three units" means three in total on the lot, with the existing house counted. It is not three units on top of the house.
In the statute's words
- Three units, 30-A M.R.S. §4364-A(1)(A): "At least 3 dwelling units, attached or detached, inclusive of accessory dwelling units, per lot."
- ADU density, §4364-B(4)(A): "A municipality shall exempt one accessory dwelling unit on a lot from any density requirements or calculations related to the area in which the accessory dwelling unit is constructed."
- ADU parking, §4364-B(4)(C): "An accessory dwelling unit may not be subject to any additional parking requirements beyond the parking requirements of the single-family dwelling unit on the lot where the accessory dwelling unit is located."
- Owner occupancy, §4364-B(4)(E), from July 1, 2027: "A municipality shall allow the construction or occupancy of an accessory dwelling unit on a lot even if the owner of the lot where the accessory dwelling unit is located does not reside in a dwelling unit on that lot."
- Size, §4364-B(6): "An accessory dwelling unit must meet a minimum size of 190 square feet."
Limits that still apply
- Septic lot size. The state minimum lot size for subsurface wastewater (Title 12, chapter 423-A) still controls on septic.
- Shoreland. Shoreland zoning still applies.
- Town carve-outs. A town may exempt coastal barrier, special flood hazard and coastal sand dune areas by ordinance.
- Dimensions. Each unit still meets the lot's setbacks and other dimensional rules for a single-family home.
- Lot size caps. LD 2173 added limits on how large a town's minimum lot size can be in some areas, for example no more than 5,000 sq ft in a growth area with public water and sewer (§4364-A(2-A)).
Related changes on the same date
- ADUs with two- and three-unit buildings. From July 1, 2027, a town must allow an ADU on a lot with a two- or three-unit building, not only a single-family home (§4364-B).
- No owner-occupancy rule. A town may not require that the owner live on the lot (§4364-B(4)(E)).
- No planning board review for small projects. A town may not require planning board approval for an ADU, or solely because a project creates four or fewer units in one building.
- Subdivision threshold. LD 1829 raised the subdivision trigger from three dwelling units to five (30-A M.R.S. §4401(4)).
- Parking in growth areas. LD 427 (Public Law 2025, chapter 374) bars a town from requiring more than one off-street space per unit for housing in a designated growth area, also from July 1, 2027 (30-A M.R.S. §4364-F).
What we found in local ordinances
Several York County ordinances we read in November 2026 still limit a lot to two units or still require the owner to live on site. Kennebunk, for example, still bars a third unit on a lot that has a house and an ADU. Until July 1, 2027 the town text governs those points. After that date, the statute does.
Is anything newer pending?
We found no bill pre-filed for the 2027 session that would change the three-unit rule, but the list of pre-filed bills was not complete when we checked. We will update this post if that changes.
Bring the lot to a land review and we will check it against both the town ordinance and the statute.
The 2-minute calculator is on instant pricing. Published packages are on the ADU models.