State ADU law
Maine ADU laws: one ADU wherever homes are allowed
Maine’s law (LD 2003 of 2022, amended in 2023 and 2025) applies to every municipality.
What to do next: use this research to check your own lot and bids, then tell us about your project. Matching is not live yet, so we reply with information, not a quote.
Get ADU optionsWritten by HyreADU Research Desk Primary-source statute research
The short answer
Maine ADU laws require every municipality to allow at least one accessory dwelling unit on a lot where the main building is a single-family home or a 2- or 3-unit building. Under 30-A M.R.S. § 4364-B, the ADU can be inside the home, attached, or a new structure.
It is exempt from density limits, and it cannot be made to add parking beyond what the house needs.
As amended in 2025, a town must allow an ADU even if the owner does not live on the lot. The ADU must be at least 190 square feet, and towns may set a maximum size.
The owner must show adequate water and wastewater before occupancy. The rules applied from January 1, 2024, or July 1, 2024 in towns needing voter approval (§ 4364(1-A)).
What Maine law requires of cities
Each row is from 30-A M.R.S. § 4364-B as published by the Maine Legislature, including amendments in PL 2025, c. 385 and c. 733.
| Question | What the Maine statute says | Citation |
|---|---|---|
| Must towns allow ADUs? | Yes. At least one ADU on any lot where the principal structure is a single-family home or a 2- or 3-unit building, in any area where homes are allowed. | § 4364-B(1), (3)(A) |
| What form? | Inside an existing unit, attached to or sharing a wall with the home, or a new structure built mainly as an ADU. | § 4364-B(2) |
| Density? | One ADU per lot is exempt from density limits. | § 4364-B(4)(A) |
| Parking? | No parking beyond what the single-family home requires. | § 4364-B(4)(C) |
| Owner-occupancy? | Towns must allow an ADU even if the owner does not live on the lot. | § 4364-B(4)(E), added by PL 2025, c. 385 |
| Setbacks? | An attached or internal ADU uses the same setbacks as the home. ADUs in existing garages or outbuildings use that structure’s setbacks. | § 4364-B(4)(B) |
| Size? | At least 190 square feet. A town may set a maximum. | § 4364-B(6) |
| Unpermitted ADUs? | An ADU built without approval must be allowed if it otherwise meets the rules. | § 4364-B(4)(D) |
Maine ADU rules set by state law, as read on the official statute page on October 27, 2026.
Who the law covers and when it took effect
The section applies to all Maine municipalities, with an exception for lots in certain unfiltered drinking-water watersheds serving Lewiston and Auburn (§ 4364-B(1-B)).
The “implementation date” is January 1, 2024 for towns whose officers can enact ordinances directly, and July 1, 2024 for all others (§ 4364(1-A)). Later amendments in 2025 extended the rule to 2- and 3-unit buildings and removed owner-occupancy requirements; the 2025 session laws set their own effective dates.
What is still up to your city or county
Towns may set a maximum ADU size, impose fines for code violations, and keep shoreland zoning in force, though they may not ban ADUs from the shoreland zone outright (§ 4364-B(5), (8)).
Before occupancy, the owner must give written proof of adequate water and wastewater: a sewer connection with capacity, or a septic system verified by the local plumbing inspector (§ 4364-B(7)). For septic questions, see our ADUs on septic systems research.
How to check your own city
Answer these in order, in writing, before you pay for drawings.
- 1 Check your town’s ADU maximum size
The state sets only the 190 square foot minimum.
- 2 Confirm wastewater capacity early
You will need written proof before occupancy. For septic, a licensed site evaluator prepares the plans.
- 3 Check shoreland zoning
If your lot is in the shoreland zone, those rules still apply.
- 4 Ask whether the town ordinance reflects the 2025 amendments
Older ordinances may still list an owner-occupancy rule.
What this page does not cover
This page covers the Maine statute only. It does not cover building codes, septic and well rules, HOA covenants, flood or wildfire overlays, or your city’s fee schedule. Those can still stop a project the statute allows.
We read the statute on October 27, 2026. Laws change, and courts read them.
If your project depends on one clause, have a land-use attorney or the planning department confirm it for your parcel.
For the national picture, see which states have ADU laws; for what to ask at the counter, see the ADU permit guide.
Questions
Can I build an ADU anywhere in Maine?
Do I have to live on the property for a Maine ADU?
Is there a minimum ADU size in Maine?
Does a Maine ADU need parking?
Written and audited by
HyreADU Research Desk
Primary-source research, data analysis and fact checking
We are a research desk, not a builder. We read the permit extract, the statute, the HCD return or the fee schedule ourselves, and publish each figure with its source and retrieval date.
Where a number cannot be traced to a primary source, we leave it out and say what we could not verify. Our store-based claims cover California only.
- CA
- the only state this desk will make store-based claims about
- 5
- jurisdictions with extracted ADU permit evidence
- 735
- CSLB-verified companies in the California store
- 0
- national claims from a one-state store
How this desk works
- Primary sources only. Permit counts come from the city or county that issued the permit. Production counts come from HCD’s Annual Progress Report. Rents come from HUD or the Census. We do not cite an article that cites a source; we download the source and compute the figure ourselves.
- This is a California site. The company store is 734 California firms and one New Mexico firm. Permit evidence exists for five named jurisdictions: Los Angeles, San Francisco, Sacramento, San José and unincorporated Marin. A number from that store is titled to those places, never to the United States.
- A permit is not a completion, and a license is not an ADU grade. California licenses no ADU classification. Being named on an ADU permit is evidence of engagement in that jurisdiction, not of quality, completion, or work anywhere else. Owner-builder permits are excluded from contractor counts.
- Calculation is labeled as calculation. Figures we derive are never presented as something HCD, HUD, the Census or a city published. Terner Center research is cited as Terner’s, never restated as ours.
- We do not design, permit or build ADUs, and we take no payment for placement, ranking or a favorable mention. Pages that look like rankings are not: they publish public-record counts and let the reader decide.
- Nothing here is legal, tax or financial advice. Zoning, underwriting and appraisal practice vary by jurisdiction, lender and appraiser. The useful next step on a specific lot is the planning counter and a licensed professional.
Data as of 30-A M.R.S. § 4364-B read on legislature.maine.gov, retrieved 2026-10-27.. Authorship on this site is organizational: the analysis belongs to the desk rather than to a named individual, and we do not publish credentials we do not hold. Our editorial policy sets out how we source, date and correct what we publish.
Sources & retrieval dates
- 30-A M.R.S. § 4364-B, Accessory dwelling units , Maine Legislature, Maine Revised Statutes Retrieved October 27, 2026.
- 30-A M.R.S. § 4364, subsection 1-A (implementation date) , Maine Legislature Retrieved October 27, 2026.
Planning an ADU in Maine?
Tell us about your lot and what you want to build. Matching is not live yet, so this is not a quote. We will send ADU options and the next questions to ask your city.
HyreADU is a publisher. It does not design, permit or build ADUs, and matching with builders is not live yet. This page describes state statutory text as published on the retrieval date.
It is not legal advice. Your city or county applies the rules to your lot, and its planning department is the authority for your parcel.