LD 2003 Explained (2026 Update): What Maine Homeowners Can Build
LD 2003 (Public Law 2021 ch. 672) requires every Maine town to allow at least one ADU on a lot with a single-family home, with no extra parking and without counting it against local growth caps. Later laws built on it: LD 1829 (2025) bars towns from requiring the owner to live on the property, rules out planning board approval for ADUs, and raises the minimum to three homes per residential lot (four in growth areas or where public water and sewer are available); LD 2173 (2026) clarified LD 1829, extended ADU rights to lots with 2- or 3-unit buildings, and gave towns until July 1, 2027 to update ordinances. None of this removes the building permit, building code, or septic and water requirements.
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Last updated: 2026-10-10 | Author: Place Buildings Editorial Team | Reviewer: Place Buildings Project Review Team
Maine ADU law today vs. what your town can still require
| Topic | What state law says now | What your town can still require |
|---|---|---|
| Where ADUs are allowed | At least one ADU on any lot with a single-family home, or a 2- or 3-unit building, wherever residential use is allowed (LD 2003; expanded by LD 2173) | Building permit, code-compliant plan set, and MUBEC compliance |
| Owner living on site | Towns cannot require the owner to live in the house or the ADU (LD 1829) | Short-term rental rules, which can include limits on renting ADUs short-term |
| Board approval | No planning board or zoning board approval required for an ADU (LD 1829, clarified by LD 2173) | Site plan review, historic preservation review, and code office staff review |
| Homes per lot | At least 3 homes on any residential lot, 4 in a growth area or where public water and sewer are available; an ADU can be one of them (LD 1829, clarified by LD 2173) | The same dimensional standards as a single-family home, plus proof of water and wastewater capacity |
| Parking | No parking for the ADU beyond what the house already requires (LD 2003) | The parking requirement for the house itself |
| Size | Minimum 160 sqft, set by the state building codes board in March 2025 | A maximum ADU size |
| Growth caps | ADU permits do not count toward a town rate-of-growth limit (LD 2003) | Growth caps on other new housing |
| Shoreland | Towns cannot ban ADUs outright in the shoreland zone (LD 1706) | State and local shoreland zoning standards |
| Sprinklers | Not required unless the ADU is in or attached to a building with more than two units, counting the ADU (LD 1829) | Fire and life-safety requirements under building code |
| Septic and water | Once the local plumbing inspector verifies adequate wastewater, the town cannot add more wastewater review (LD 1829) | Septic design by a licensed site evaluator and proof of potable water or utility connection |
How Maine ADU law has changed since 2021
| Law | Signed | What it changed for homeowners |
|---|---|---|
| LD 2003 (P.L. 2021, ch. 672) | 2022 | ADUs allowed by right next to single-family homes; no extra ADU parking; ADUs exempt from growth caps; more than one home per residential lot; affordable housing density bonus |
| LD 1706 (P.L. 2023, ch. 192) | 2023 | Moved town deadlines to January 1, 2024 (council towns) and July 1, 2024 (town meeting towns); no categorical ADU bans in the shoreland zone; existing unpermitted ADUs allowed if they meet the rules |
| LD 1829 (P.L. 2025, ch. 385) | 2025 | No owner-occupancy requirements; no planning board approval for ADUs; at least 3 homes per residential lot (4 in growth or water-and-sewer areas); sprinkler limits; no extra wastewater review after plumbing inspector sign-off |
| LD 2173 (P.L. 2025, ch. 733) | April 16, 2026 | Clarified LD 1829; ADUs allowed with 2- and 3-unit buildings; towns may exempt coastal barrier, flood hazard, and dune areas; July 1, 2027 deadline for all towns to update ordinances |
What LD 2003 Started
LD 2003 is Public Law 2021 chapter 672, passed by the 130th Legislature. Its single most useful provision for Maine homeowners: on a lot with a single-family home, at least one accessory dwelling unit is allowed by right. It also barred extra parking requirements for ADUs, kept ADU permits out of local rate-of-growth caps, required towns to allow more than one home on residential lots, and created a density bonus for affordable housing developments.
Towns originally had until July 1, 2023 to update their ordinances. LD 1706 (2023) moved that to January 1, 2024 for towns with a council and July 1, 2024 for towns run by town meeting, so the core LD 2003 ADU rules now apply in every Maine municipality.
What Changed in 2025 and 2026
LD 1829 (Public Law 2025 chapter 385) is the biggest update since LD 2003. It explicitly bars towns from requiring the owner to live on a lot with an ADU, rules out planning board approval for ADUs, raises the minimum number of homes towns must allow on a residential lot to three (four in designated growth areas or where public water and sewer are available), limits when towns can require fire sprinklers in an ADU, and stops towns from adding their own wastewater review once the local plumbing inspector has signed off.
LD 2173 (Public Law 2025 chapter 733), signed April 16, 2026, cleaned up LD 1829. It confirmed that an ADU is allowed on a lot with a 2- or 3-unit building, not only a single-family home, let towns exempt coastal barrier, flood hazard, and coastal dune areas, and set July 1, 2027 as the deadline for every town to bring its ordinances in line.
Practically, that means some town ordinances will lag the state law until mid-2027. The core LD 2003 rules already apply everywhere; for the newer LD 1829 and LD 2173 provisions, ask your code office how they are applying them today.
What Your Town Can Still Require
None of these laws removed permitting. Your town and the state still review the things that affect safety, neighbors, and infrastructure - they just cannot categorically refuse an ADU or send it to a planning board hearing.
- A building permit with a complete plan set: site plan, floor plans, elevations, structural details, and energy compliance documentation.
- MUBEC code compliance (Maine Uniform Building and Energy Code), covering structural, fire, energy, mechanical, and plumbing scope. See our MUBEC compliance checklist for the pre-submission review.
- Dimensional standards: an ADU inside or attached to the house follows the same setbacks and limits as the house, and for a detached ADU your town's ordinance sets the standards. Towns may choose more permissive standards for ADUs.
- Written proof of adequate water and wastewater before occupancy: a sewer connection or a septic system verified by the local plumbing inspector, and a utility connection or potable well.
- Site plan or historic preservation review where the local ordinance requires it.
- A maximum ADU size, and rules on short-term rentals.
- Electrical and plumbing permits, often issued separately from the building permit.
What This Means for a Backyard ADU
For a detached backyard ADU like our ADU 240 and ADU 400, the path is now a staff-level permit rather than a public hearing: building permit, code review, and septic or sewer verification. You do not need to live on the property, and the ADU does not need its own parking beyond what the house requires.
To count as a legal dwelling unit, an ADU must meet the state minimum size - currently 160 sqft - and full building code for a dwelling. A backyard studio used as an office or creative space is permitted as an accessory structure instead, which is a different and usually simpler path. Our ADU vs. backyard studio guide covers the difference.
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How to Use These Laws During Planning
Treat the state law as your eligibility floor - confirmation that the project is allowed in principle - and the permit process as the path to actually building.
- Save the statute citation (30-A M.R.S. section 4364-B) and bring it to your first conversation with the code enforcement officer.
- Ask whether your town has updated its ordinance for LD 1829 and LD 2173 yet; towns have until July 1, 2027.
- Verify your zone's dimensional standards - setbacks, lot coverage, height - early. These still apply.
- Document septic capacity early. A septic upgrade is still the most common late-stage surprise.
- If you plan to rent the ADU short-term, check local short-term rental rules before you design around that income.
Common Misconceptions
A few misunderstandings come up repeatedly. Naming them up front saves time and disappointment.
- "These laws mean I can skip permits." They do not. The building permit, MUBEC review, and septic or utility verification all still apply.
- "My town can refuse because the area is residential-only." That categorical denial is exactly what LD 2003 prohibits. Bring the statute citation.
- "I will need a planning board hearing." Not for an ADU. Since LD 1829, towns cannot require planning board or zoning board approval, though staff and site plan review may still apply.
- "I can place the ADU anywhere on my lot." No - setbacks, lot coverage, height, and shoreland standards still apply.
- "State law guarantees I can Airbnb my ADU." It does not. Towns can regulate short-term rentals, including in ADUs. See our rental vs. Airbnb ROI guide.
Validate For Your Property
State law makes the legal pathway clearer, but it does not tell you whether your specific lot can support an ADU. Setback geometry, septic capacity, utility distance, and access driveways all still drive feasibility. Try layouts on your lot in the Configure 3D tool, then Request a Free Property Feasibility Assessment when you want a town-specific review of zoning, permit path, and utility scope.
Frequently Asked Questions
Did LD 2003 take all permitting power away from Maine towns?
No. Towns still issue building permits, enforce MUBEC, apply dimensional standards, and can require site plan review. What state law prohibits is making ADUs categorically impossible, requiring extra parking for them, counting them against growth caps, and - since LD 1829 - sending them to a planning board.
Can my town require me to live on the property to have an ADU?
No. LD 1829 (2025) added an explicit rule that towns must allow an ADU even if the owner does not live on the lot. If your local ordinance still lists an owner-occupancy requirement, ask your code office how they are applying the state law.
Do I need a planning board hearing for an ADU in Maine?
No. Under LD 1829, as clarified by LD 2173, towns cannot require planning board or zoning board approval for an ADU. Code office staff review, site plan review, and historic preservation review can still apply.
How many units can I add to my lot?
At least one ADU on a lot with a single-family home or a 2- or 3-unit building. Separately, towns must allow at least three homes on any residential lot, and four in designated growth areas or where public water and sewer are available; an ADU can count as one of them. Water and wastewater capacity still has to support every unit, and towns have until July 1, 2027 to update their ordinances.
What is the minimum size for an ADU in Maine?
The statute sets 190 sqft unless the state Technical Building Codes and Standards Board adopts a different minimum. The board set 160 sqft in March 2025. Towns may set a maximum size.
My septic system is older. Do these laws change the wastewater rules?
No. A septic-served ADU still needs a system verified as adequate by the local plumbing inspector, with plans prepared by a licensed site evaluator. What LD 1829 changed is that once the plumbing inspector verifies it, the town cannot add its own extra wastewater review. Older systems may still need upgrading - plan for it in your budget.
My town's zoning page still says ADUs are not allowed in my zone. What now?
The core LD 2003 ADU rules have applied in every Maine town since mid-2024, and towns have until July 1, 2027 to adopt the LD 1829 and LD 2173 updates. Bring the statute citation to your code enforcement officer; an out-of-date web page does not change what state law requires.
Sources
We refresh legal and compliance references regularly to keep guidance current.
- Maine Revised Statutes, Title 30-A §4364-B: Accessory Dwelling Units (current text)
- Maine Legislature: LD 2003 (Public Law 2021 ch. 672)
- Maine Legislature: LD 1829 (Public Law 2025 ch. 385)
- Maine Legislature: LD 2173 (Public Law 2025 ch. 733)
- Maine Housing Opportunity Program: Housing Legislation Guidance (March 2026)
- Maine Housing Opportunity Program: Support for LD 2173 requirements
- Maine Subsurface Wastewater Program
Related Maine Guides
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