The Maine Agenda › Live in Maine

ADU Rules by Town in Greater Portland, Maine

Published August 8, 2026 · Updated August 9, 2026 · 17 min read

The most useful thing to know about building an accessory dwelling unit in Greater Portland is that four of the eleven towns here still have a rule in their ordinance that the state of Maine no longer permits them to enforce.

The rule is owner occupancy: the requirement that you live on the property in order to have an ADU on it. Maine removed it. Scarborough, Gorham, Westbrook and Windham have not removed it from their text. Scarborough's own public ADU page goes further and answers the question "Do I have to live on the property?" with the word yes.

We read all eleven ordinances this week to check. That finding is why this guide is organized the way it is: not as a list of what each town allows, but as a map of which rules are still yours to negotiate and which ones stopped being negotiable on July 1.

Everything below comes from the statute, from the Maine Office of Community Affairs guidance issued in March 2026, and from each town's own ordinance text read directly rather than through a summary. Where a figure comes from a document we could not confirm is current, we say so.

The floor: nine things your town can no longer do

Maine's ADU statute is 30-A M.R.S. section 4364-B. It started with LD 2003 in 2022, was amended in 2023, and was amended again by LD 1829, enacted as Public Law 2025, chapter 385. The 2025 amendments are the ones that matter now.

Your town may not prohibit at least one accessory dwelling unit on any lot where a single-family dwelling is the principal structure, anywhere residential uses are permitted, including where they are permitted as a conditional use. The 2025 amendment extended that to lots with multi-unit structures as well.

Your town may not count that one ADU against density requirements or calculations for the district.

Your town may not require additional parking for it. Not one space. This applies inside and outside designated growth areas, which is unusual: the parking rules for other kinds of housing in Maine are geographically limited, and this one is not.

Your town may not require planning board approval. The state guidance is explicit that "planning board" means any appointed or elected board or committee, and equally explicit that code enforcement review, staff review and site plan review are still allowed. The distinction is between a public board that can say no and staff who check whether you met the standards.

Your town may not require you to live on the property. This is the biggest single change, it is new in the 2025 amendments, and it is the rule most likely to still be stated the old way on a page you find, including on your town's own website. The state guidance addresses it twice, including a direct question about whether owner occupancy can be used to discourage short-term rentals. The answer given is no.

Your town may not prohibit an ADU on a lot that does not conform to current zoning, as long as the ADU does not make the nonconformity worse. It also may not refuse an ADU that was built without municipal approval, if that unit otherwise meets state and local ADU requirements.

Your town may not categorically ban ADUs in the shoreland zone. Shoreland standards still apply in full. A blanket prohibition does not.

Your town may not require fire suppression sprinklers unless the ADU sits within or attached to a structure containing more than two dwelling units, counting the ADU itself. A detached cottage behind a single-family house does not trigger a municipal sprinkler mandate.

Your town may not count an ADU permit against a rate of growth ordinance. Falmouth, for example, caps development permits at 58 a year town-wide for single-family, two-family and manufactured housing units combined. An ADU does not consume one of those. Scarborough writes the same exemption into its own ADU section at IX.J.5.

The four towns whose text has not caught up

All eleven Greater Portland municipalities enact zoning by council vote, which means all eleven were on the July 1, 2026 conformance deadline. That date has passed. Six towns have deleted owner occupancy from their ADU text. Four have not.

Scarborough still prints it at Section IX.J.1 of its zoning ordinance: "The owner(s) of the lot on which the principal structure is located must reside in the principal structure or the accessory dwelling unit, either of which residence may be seasonal." The section carries an amendment date of 05/20/2026, which means it was opened and edited after the state bar took effect and the clause survived the edit. Scarborough also caps ADU occupancy at two persons.

Gorham still prints it at Section 300-2.29.A: "The owner(s) of the lot must reside in the principal structure or in the accessory apartment." Subsection G adds that noncompliance means the apartment "shall be discontinued, and the lot shall revert to single-family use." Gorham's section is still titled "Accessory apartments" and was last amended in January 2023, before either the 2023 or 2025 rounds of state law.

Westbrook still prints it at Section 335-2.2.E(5): "The owner of the principal structure must reside in either the principal dwelling unit or the ADU. This restriction shall be included in the certificate of occupancy." Westbrook's ADU section was amended on December 4, 2023, after LD 2003, and the clause was kept.

Windham prints it at Section 501.B of its Land Use Ordinance and then builds a second enforcement mechanism on top of it. Section 501.F(1) provides that an ADU permit "shall be issued to the property owner and not run with the land," that a sale requires the new owner to obtain a fresh permit, and that a unit out of compliance at transfer must be fixed within thirty days or the code officer "shall cause the use of the accessory apartment to be discontinued." Every permit is recorded at the Cumberland County Registry of Deeds. It is the most aggressive ownership tie in the region.

What to do with this if you are the homeowner: get the conflict in writing rather than arguing it at a counter. Ask your code enforcement officer, by email, which authority the owner-occupancy requirement is being applied under given 30-A M.R.S. section 4364-B as amended by Public Law 2025 chapter 385. A printed ordinance clause and a state statute that overrides it are a question for the town attorney, not for a permit clerk, and you want the answer dated and attributable. We are describing what the documents say. We are not your lawyer.

Portland, South Portland, Falmouth, Cape Elizabeth, Freeport and Cumberland have all removed the clause. Portland's deletion arrived with the Land Use Code revision effective July 1, 2026, and it is worth knowing that the 2022 edition of Chapter 14 did print an owner-occupancy requirement, with a carve-out for legally nonconforming lots on Peaks Island. If you are reading a Portland PDF that mentions Peaks Island in the ADU section, you are reading the old one.

Yarmouth is the one town where we did not resolve this. Its ADU guide is dated May 2024 and therefore predates the 2025 amendments, and we did not read its current ordinance text on this specific question. Ask.

The number nearly every ADU page gets wrong

The statute says an ADU must be at least 190 square feet, and then says that if the Technical Building Codes and Standards Board adopts a different minimum, the Board's number governs.

The Board adopted a different number. According to the March 2026 state guidance, the minimum size has been 160 square feet since the Board set it in rule in March 2025.

So 190 is the number printed in the statute and 160 is the number that actually applies. Yarmouth saw this coming and drafted around it: rather than write a figure into its ordinance, Yarmouth's standard simply points at whatever the Board has adopted. That is the correct way to write a local rule on top of a state rule, and it is worth noticing because most towns did the opposite. Cape Elizabeth, Scarborough, Freeport, Westbrook and Windham all print 190 in their own text.

What your town still controls

Four things, plus money.

Maximum size. The state sets a floor and no ceiling. Towns set the ceiling, and this is where the real variation lives, from 600 square feet in Windham to no cap at all in Cumberland.

Short-term rentals. The state guidance is direct: a town cannot use owner occupancy to stop ADUs becoming short-term rentals, but it can regulate short-term rentals as such. Whether your ADU can go on Airbnb is a question for your town's short-term rental ordinance, not its ADU ordinance, and those diverge sharply across the region. Our short-term rental rules by town guide covers which six towns run a registration program and what each charges. Cape Elizabeth is the outlier that handles it inside the ADU section itself, at 19-7-5.B.7, which prohibits short-term rental use of an ADU outright.

Process and review. Site plan review, historic district review and code enforcement review all survive. So does the written verification that your water and wastewater can carry a second household, which is a real constraint and not a formality. In Gorham it means a Portland Water District ability-to-serve letter before the building permit issues. In Windham it means a septic system approved for two dwelling units and an HHE-200 form recorded at the registry of deeds, which on a rural lot is more likely to stop your project than any square-footage rule.

Design standards. Towns can still regulate entrances, exterior appearance and setbacks, as long as their setback rules for ADUs are no stricter than for the principal dwelling.

And fees. Nothing in state law caps what a town charges, which is why the cost of the same project varies by roughly ten times across a twenty-five minute drive.

All eleven towns

Sizes first, because that is the number that decides whether the project you have in mind is possible where you live.

Two notes on that table. Portland's rule is a ratio rather than a number, so on a large house it is the most generous in the region, and Portland is the only town that lets you build two. Cumberland's blank is real and not a gap in our reading: the 11-24-2025 amendment deleted the old 40 percent and two-bedroom limits, and the commercial ADU sites still quoting those figures for Cumberland are quoting a repealed rule.

Fees, and the town nobody expects to be the expensive one

Windham is the most expensive place in Greater Portland to permit an ADU, by a wide margin. The application fee is 100 dollars, the building permit runs 50 cents per finished square foot, and then two impact fees land: 400 dollars recreational and 225 to 411 dollars for open space depending on bedroom count. A 600 square foot one-bedroom unit therefore starts around 1,025 dollars before a single other charge. Figures are from the town's Master Fee Schedule approved 7/12/2022 by Order 22-125.

South Portland is second and front-loads it differently: a 500 dollar zoning permit, split into a free pre-application meeting, a 200 dollar application meeting and a 300 dollar submittal fee, all before the building permit. Budget three to four weeks for zoning review and four to six for the building permit, which can run simultaneously. Most applications involve no public hearing. Code Enforcement is at 207-767-7603.

Yarmouth charges 150 dollars for administrative review plus 5 dollars for each abutter notification letter within 500 feet, and expects six to eight weeks. Before you get a building permit you must record a declaration of restrictions at the registry stating the unit will not be sold separately. Yarmouth does not regulate rentals shorter than 30 days in any dwelling unit, so an ADU there can be a short-term rental.

Everyone else charges the ordinary building permit rate with no ADU-specific fee at all: Scarborough at 50 cents per finished square foot with a 50 dollar minimum, Cumberland at 40 cents finished with a 50 dollar minimum, Freeport at 40 cents with a 55 dollar minimum and no impact fee below 1,000 gross floor area, Gorham at 12 dollars per thousand of project value with a 50 dollar minimum, Cape Elizabeth at 1.2 percent of project value. Portland charges the building permit plus city impact fees.

Two fee items we could not confirm. Westbrook's ordinance defers entirely to a City Fee Schedule set by the council, and we could not locate that schedule. Cape Elizabeth's schedule prints a half-price ADU rate of 0.6 percent that expired on 5/1/2025 and does not say what replaced it, so the standard 1.2 percent is our reading rather than the document's statement. Call the code office before you budget either one.

Review process

This part is the good news and it is nearly uniform. All eleven towns run ADUs through the code enforcement officer at staff level. No planning board anywhere in Greater Portland can vote your ADU down. Cape Elizabeth has one carve-out worth knowing about, in the Town Center Core Subdistrict, where site plan review is not waived the way it is elsewhere in town.

Yarmouth's May 2024 guide states that the Planning Director may refer an application to the Planning Board for a public hearing, which sits uneasily beside the state guidance that planning board approval may not be required. If that comes up, it is another question worth asking in writing.

The clauses that will actually stop you

Size and fees are what people research. These are what kill projects, and each is buried mid-section in an ordinance nobody reads to the end.

Cumberland bars an ADU outright on a lot with a nonconforming use, and grants no variances on size, height, setbacks, lot coverage or frontage for ADUs.

Freeport does not count an ADU toward density outside the shoreland zone, but does count it inside, and caps total dwelling units per lot at three, or four in a designated growth area.

Windham applies its ADU standards only to units created after November 23, 2012, and requires the unit be attached to the principal dwelling or contained within an accessory building, which appears to leave no route to a freestanding purpose-built cottage.

Westbrook permits an ADU only as an accessory to a single-family dwelling, not to a duplex or multifamily building, and provides that if the city adopts a short-term rental ordinance, ADUs fall under it automatically.

Gorham requires connection to public sewer and the public water main where available, and limits occupancy to two people.

Portland caps detached ADUs at 18 feet in height, or 25 above a garage, and forbids siting one between the principal structure and the front lot line. Portland's own zoning FAQ still warns that an ADU "may require installation of a new sewer line and installation of a fire sprinkler system." The sewer half is real. The sprinkler half is now narrower than that sentence suggests. Zoning staff are at 207-874-8709.

The deadline question, answered

LD 1829 took effect on September 24, 2025, and municipalities were given time to conform. The implementation deadline is July 1, 2026 for municipalities whose council can enact ordinances on its own, and July 1, 2027 for town meeting municipalities.

Every municipality in this guide is in the first category. We checked each one against its own charter rather than assuming from its name, and the two that look like exceptions are not. Windham is called a town and has a council-manager charter under which the planning board only recommends. Gorham's charter gives its council all the powers of a town meeting subject to an Article IX proviso, and Article IX turns out to be initiative and referendum, meaning a citizen petition can force a vote on a council ordinance but zoning does not have to go to one by default. Cape Elizabeth has the same structure and its citizens actually used that overrule mechanism against an unrelated 2025 town center amendment.

So the deadline for all eleven passed on July 1, 2026. That is a change from what most pages on this subject will tell you, and it is the single fact that turns four of those printed owner-occupancy clauses from an open question into a conflict.

One more thing on the horizon: a bill numbered LD 2173 has been proposed to clarify parts of LD 1829, including replacing the phrase "multi-unit structure" with "two-unit or three-unit residential structure." It had not been enacted as of the March 2026 state guidance. Do not plan a project around it.

A warning about searching for this

Three traps, and the third one is new to us this week.

Search for Portland ADU rules and the top result is likely to be portland.gov, which is Portland, Oregon, whose ADU code is Chapter 33.205. Portland, Maine is portlandmaine.gov and its code is Chapter 14. The Oregon page will tell you the maximum is 75 percent of the living area or 800 square feet. Both numbers are wrong here. Search for Falmouth ADU rules and you will get falmouthma.gov and its Zoning Bylaw Section 240-9.1, which is Falmouth, Massachusetts. Our Falmouth is falmouthme.org. The same problem exists for Freeport, which is also in Florida, Texas, Illinois and New York; for Gorham and Windham, which are also in New Hampshire; for Westbrook, which is also in Connecticut and Minnesota; and for Scarborough, which is also in New York, Ontario and England.

The second trap is the commercial ADU pages that rank well for these queries. They are templated, and several of them describe Maine towns as still requiring owner occupancy for seven months of the year. The irony this week is that they are accidentally right about four towns and wrong about the reason.

The third trap is the towns' own websites. Cape Elizabeth's main navigation links a zoning ordinance PDF that is two amendment cycles out of date, in which the ADU content differs from the current version. Portland's search results surface the March 2022 edition of Chapter 14 ahead of the June 2026 one, and the difference between them is the owner-occupancy clause. Gorham's only linked permit fee schedule is a scan dated August 2021 that still cites a domain the town has retired. Check the effective date printed on the cover of any municipal PDF before you trust a number in it.

If you are weighing an ADU as an income property rather than a place for a parent, the arithmetic runs through property taxes by town and, if you plan to rent long term, through rent increase rules by town. Smaller yard projects follow the same pattern of the town line mattering more than the state line, which is why the region's fence rules range from no height limit at all to a permit for every fence.

FAQ

Do I have to live on the property to have an ADU in Maine?

No. Public Law 2025, chapter 385 requires municipalities to allow construction and occupancy of an ADU even when the lot owner does not live in any dwelling on the lot, and the state guidance confirms a town may not require owner residence in either unit, including as a way to discourage short-term rentals. Four Greater Portland towns still print the old requirement in their ordinances: Scarborough, Gorham, Westbrook and Windham. Scarborough's public ADU page still answers this question with yes.

Which Greater Portland town allows the largest ADU?

Cumberland, which deleted its maximum size entirely on November 24, 2025 and now sets no square-footage cap at all. Cape Elizabeth's 1,200 square feet is the largest fixed number, and its conversions of accessory structures that existed on January 1, 2023 are exempt from even that. Portland's two-thirds-of-the-principal-unit ratio can exceed both on a large house, and Portland is the only town in the region that permits two ADUs on one property.

How much does an ADU permit cost near Portland, Maine?

Windham is the most expensive: a 600 square foot one-bedroom unit runs about 1,025 dollars, being a 100 dollar application fee, roughly 300 dollars of building permit at 50 cents per finished square foot, a 400 dollar recreational impact fee and a 225 dollar open space impact fee. South Portland charges 500 dollars for the zoning permit alone before the building permit. Yarmouth charges 150 dollars plus 5 dollars per abutter letter. Most other towns charge only the ordinary building permit rate with no ADU-specific fee.

What is the minimum size for an ADU in Maine?

160 square feet. The statute names 190 square feet but defers to the Technical Building Codes and Standards Board, and according to the state's March 2026 guidance the Board set the minimum at 160 square feet in rule in March 2025. Several Greater Portland ordinances still print 190 in their own text, including Cape Elizabeth, Scarborough, Freeport, Westbrook and Windham.

Can a planning board stop my ADU in Greater Portland?

No. Maine law prohibits municipalities from requiring planning board approval for an ADU, and all eleven Greater Portland municipalities run ADUs through the code enforcement officer at staff level. Staff-level code enforcement review, site plan review and historic review are all still permitted. The one local carve-out we found is Cape Elizabeth's Town Center Core Subdistrict, where site plan review is not waived.

Has the deadline for towns to update their ADU rules passed?

Yes, for every municipality in Greater Portland. The state set July 1, 2026 for municipalities whose council can enact ordinances on its own and July 1, 2027 for town meeting municipalities, and all eleven towns covered here enact zoning by council vote, which we confirmed against each town's charter. Windham and Gorham both look like exceptions by name or charter language and are not.

Does my town have to give me extra parking relief for an ADU?

Your town cannot require any additional parking for an ADU, anywhere in Maine, inside or outside a growth area. This is stronger than Maine's general housing parking rules, which are limited to designated growth areas. Windham's ordinance text still cross-references its parking sections for accessory apartments, which is another clause the state bar now reaches.

Can I rent my ADU on Airbnb?

That depends on your town's short-term rental ordinance, which is a separate body of rules from its ADU ordinance. Yarmouth does not regulate rentals under 30 days at all. Cape Elizabeth bans short-term rental of an ADU inside the ADU section itself. Westbrook provides that ADUs fall automatically under any short-term rental ordinance the city later adopts. Portland, South Portland, Falmouth, Cape Elizabeth, Freeport and Scarborough all run registration programs, covered in our short-term rental guide.