ADU FAQs

No.

The law establishes new housing density requirements under Title 30-A, which governs municipalities. Land use in the LUPC service area is governed under Title 12, and as a result, the provisions of LD 1829 do not extend to the towns, plantations, and townships overseen by the Commission.

Residents considering adding an ADU on a property in Maine’s Unorganized and Deorganized Territories should contact their regional permitting representative to discuss applicable current and potential future standards and permitting requirements.

Future consideration of ADUs in the LUPC service area:
Accessory Dwelling Units will be considered as part of the LUPC’s upcoming update to its Comprehensive Land Use Plan (CLUP), the Commission’s guiding policy document. The CLUP update is a multi-year, stakeholder-driven process that is currently in the planning stage. Any future rule changes related to ADUs would originate through that process or through additional action by the Legislature.

Members of the public and media are encouraged to subscribe to LUPC email notifications to stay informed about the CLUP update and other important land-use matters.

Every town may apply its own ADU rental policies, so it’s essential to check with your local Planning Department or Code Enforcement Office to determine whether short-term rentals are allowed, if there’s a required minimum rental period, or if owner-occupancy is mandated.

Renting an ADU comes with many responsibilities, including understanding local and state housing laws, executing a lease, finding and managing a tenant, and maintaining a rental property. It’s important to understand the laws as they may affect things like future rent increases, changing use over time, evicting tenants, and moving family into the unit. See our blog post about renting your unit for more details.

If moving friends or family into the unit, it’s still highly important to have a written agreement. Consult a lawyer or find an agreement template by searching online for phrases like “family rental agreement.”

Municipalities require both final inspections and a Certificate of Occupancy. Once the inspection is complete and the certificate issued, your ADU is ready for move-in—just be sure utilities are connected, an address is assigned, and all final preparations are in place.

See our blog post about renting your unit for more details about renting out the unit to long-term tenants. If moving friends or family into the unit, it’s still highly important to have a written agreement. Consult a lawyer or find an agreement template by searching online for phrases like “family rental agreement.”

Traditional construction will take 6-12 months, though this will vary depending on the specifics of the project. Stages of construction include:

• Prepping site & foundation: 1–2 months
• Framing & exterior: 1–2 months
• Systems & insulation: 1–2 months
• Finishes & final inspection: 1–2 months

Modular construction can take 4-6 months for materials to be ordered and completed in a factory, and another 4-8 weeks for finishing. State law requires licensing for manufactured housing.

Construction costs (also called “hard costs”) for your ADU will vary significantly depending on personal preferences, site conditions, location, and many other factors. Hard costs typically total around 85% of your total project budget.

See the budgeting page for more details.

If you are not using a design/build firm, you will need to find a contractor to take over for the construction phase of your ADU.

First, you’ll solicit bids from potential contractors. You will want to get at least three bids for comparison and judge them based on completeness, experience, references, and cost. Before you hire someone, make sure to check their license and insurance and when they present you with a contract, review everything carefully.

Maine does not have a licensing program for builders, but before hiring anyone, be sure to verify their insurance and review their contract carefully.

When building an ADU, utilities such as water, sewer, and electricity are an important part of the permitting and construction process. Municipalities may require separate or shared connections to water and sewer, but they cannot make ADU utility requirements more burdensome than what is typically required for a new home or other accessory structure. Water districts in Maine commonly require separate meters and connections.

If public sewer/water is not available, proof of capacity for on-site septic and well systems may be required by the local plumbing inspector or code officer. Fees must be proportionate and not excessive compared to other similar structures.

While local ordinances vary, ADUs can usually share an electric meter with the primary residence or apply for a separate service/meter through the utility provider. It depends on usage needs and rental plans.

Some municipalities (e.g., Portland) may require a drainage or stormwater review, especially for detached ADUs that increase impervious surface.

ADUs can be charged a variety of fees from your local government, the State, and other agencies. Some fees are based on details of the project while others are fixed. The total amount depends highly on your property and plans.

Typically, ADUs in Maine can expect to incur the following fees:

• Planning review: $100–$300
• Building permit: $10–$15 per $1,000 of project cost
• Impact fees: Vary by town; often waived for ADUs under 750 sq ft
• Utility hook-up or connection fees

Submitting an application is different in each community. Some have online portals while others ask for multiple sets of paper copies on various sizes of paper. Some locations require one application package, while otherwise require separate processes from the Planning and Building departments. Check with local Planning staff to confirm the application process and requirements and for details about permit materials.

Design costs cover the work of your architect or designer and may or may not include engineering, surveying, and other professional services necessary to prepare for permitting. Together, these services may total around 10% of your total project budget – the exact amount depends on the details of your property and project. See the budgeting page for more details.

Once you have a design established with your architect/designer, it’s a great idea to discuss it with Planning staff so they can point out any issues before you prepare your application.

Most homeowners choose to work with some type of design professional to plan their ADU and help throughout the process. Bringing on a professional early in the process is often key to getting your ADU approved quickly, managed efficiently, and built cost-effectively. Relevant experience and fit will be critical.

There are a variety of types of designer, and they may be an architect, builder, “designer,” design/build, or a modular/prefab company. If you’re hiring a local individual or team, they’ll likely start the process by visiting your home and talking to you about your ideas and goals. If it seems like a good match, they will prepare a proposal detailing their services and fee. Professionals typically charge for an initial consultation or proposal.

Check our professionals directory to see if there’s a good fit for your project.

Rental income is a major benefit of having an ADU on your property – for many people, it provides flexibility in their budget or an opportunity to grow their savings. Sometimes funding products will take into account the potential rental income and/or value increase of your property to help you pay for your project.

Make sure you understand the short-term rental rules for your community.

No, not by default—but there are exceptions with specific legal steps.

LD 2003 Does Not Require Separate Sale Rights

Maine’s state law (LD 2003) does not mandate or guarantee the ability to sell an ADU separately from the primary home. In fact, in most cases, you cannot sell it as a standalone unit because:

• The ADU and primary home share the same lot.
• There’s typically only one legal property title (deed) for the parcel.
• ADUs are generally considered accessory structures, not separate dwellings for sale.

When Can an ADU Be Sold Separately?

To sell an ADU separately from the main home, you would generally need to:

• Divide the property through:
  • A subdivision or condominium conversion, and
  • Get approval from the local planning board or code office.
• Create separate utilities, legal access, and possibly a new lot (or condo unit).
• Record separate deeds or ownership structures.

This is a complex process and not commonly pursued in Maine unless part of a condo or multifamily development.

In Practice (Maine Municipalities): Most towns do not allow ADUs to be sold separately without a full subdivision or condominium process. Some municipalities may explicitly prohibit separate conveyance in their ADU ordinances.

Your taxes will increase only based on the value of the new ADU. Contact your local Assessor’s Office for a site-specific estimate.

If you have equity in your home, a cash-out refinance or home equity loan/line of credit (HELOC) might work for you. Financing is typically unavailable for homeowners with lower income and insufficient home equity.

Many homeowners use a mix of options to finance their ADU, including savings, funds from family, and/or loans. It is strongly recommended that your financing is in place before construction starts. Be sure to factor in potential rental income since that will help you repay loans.

With more Mainers interested in building ADUs and towns loosening zoning rules, new loan options are now available that are tailored to ADU projects.

Unlike refinancing an existing mortgage—which can lock homeowners into higher interest rates—ADU loans are typically offered as a second mortgage with repayment terms of up to 30 years. They are also based on the “as-complete” value of the home after the ADU is built, giving borrowers access to more funds for design, permits, and construction.

These loans usually feature fixed interest rates and allow interest-only payments during construction, making monthly costs more predictable and easier to manage.

Check our professionals directory for a selection of banks and financial institutions that might work for you.

You’re not required to tell your neighbors about your ADU, but it’s always a good idea to communicate with them early in the process. Your project will run more smoothly if they are kept informed, and they may have great ideas for your project!

If you live in a Neighborhood or Homeowners Association, talk with your representative or board early in the process. HOAs or subdivision deeds can explicitly restrict ADUs, rentals, multi-dwelling units, and similar uses.

An unpermitted ADU can make it difficult to sell or refinance your property. If the ADU is being built, the City or County can stop construction and increase permitting and inspection fees. Existing unpermitted ADUs can go through the permitting process, and local staff will work with you to determine what would be involved to bring your ADU up to code.

If you already have an ADU on your property that was built without permits, you may be wondering how Maine’s new housing law (LD 2003) affects your situation. Here’s what you need to know:

Under LD 2003, the Unpermitted Units aren’t “Grandfather”, therefore LD 2003 does not automatically legalize unpermitted ADUs. Homeowners with existing, unpermitted units must still go through the local permitting process to bring their ADU into compliance. You may be able to retroactively permit the unit if it meets current zoning, building, life safety, and utility requirements.

What You Can Do If You Have an Unpermitted ADU:

• Contact your local Code Enforcement Officer or Planning Department
  • Ask what the process is to legalize an existing ADU.
  • They may require inspections, as-built drawings, or upgrades to meet current code.
• Prepare for inspections and possible upgrades
  • You may need to upgrade electrical, plumbing, egress, or fire safety components.
  • In some cases, structural work may be needed if the unit doesn’t meet building code.
• Check zoning compliance
  • LD 2003 may make it easier to legalize your unit if it now meets the new standards (e.g., no lot size minimums, reduced parking, etc.).
  • However, if the unit violates setback, size, or health/safety rules, it may not be permitted even under LD 2003

Be Aware of Possible Penalties

• Some municipalities may charge double permit fees or issue notices of violation if an unpermitted unit is discovered.
• However, many towns are willing to work with property owners to bring units into compliance—especially in support of affordable housing goals.

There are two types of construction to consider and both have pros and cons, so think about the level of customization you want and how the ADU will work on your property.

Site-built ADUs

Traditionally constructed and built from scratch on your property (AKA “stick-built”), which often slows for a lot of customization and smaller changes throughout construction.

Typical benefits:

• More options for customization
• Can be easier to get financing and permits
• Can be easier to place on unique properties (steep slopes, rocky terrain, small spaces)
• Can typically be paid for phase-by-phase

Prefab, modular, and panelized ADUs

Built in a factory, then shipped to your site and assembled or placed on a foundation. Some companies provide  “turnkey” service with support through the entire process (permitting, construction, etc.). If not, you’ll need to hire other professionals to help.

Prefab ADUs are categorized based on how they are built and inspected.

• Partially-fabricated (panelized, framing kits) Parts of the ADU are built off site at a factory, and construction follows a traditional site-built pattern. Local inspectors check work at different stages and a local general contractor and their crew are responsible for putting all the pieces together and passing inspections.
• Prefabricated (modular, manufactured, factory-built) The ADU is built and inspected for building code off site at a factory, then delivered and put in place on your property by a crane or tow. Local inspectors only check work like foundation and utility hook-ups. These types are all built similarly but are called different things based on what building code they meet (state, federal, etc.).

It’s important to note that prefab ADUs may cost the same as site-built ADUs – transportation, crane, foundation, and sales tax can end up being 20-40% of the total cost. When you get in touch with prefab companies, be sure to ask what is included in the price. Some companies do offer a lower price point.

Typical benefits:

• Lower design and engineering costs
• More clarity on what you’ll get in the end
• Faster construction with less on-site disruption
• Quality inspections from the start
• Fewer permits and inspections

 

General ADU cost estimates in Maine:

• Interior Conversion ADU: $30,000 – $100,000
• Garage Conversion ADU: $60,000 – $150,000
• Attached New ADU: $100,000 – $300,000
• Detached New ADU: $200,000 – $500,000

This cost varies widely based on your design and the requirements of your site and local municipality. See Budgeting for more detailed information on costs and financing for your ADU.

Building an ADU is an investment of time as well as money. Most projects take 12-24 months to complete, with interior conversions being the fastest.

• Planning (learning the rules, setting goals, budgeting): 1-3 months
• Design: 1-6 months
• Permitting: 1-6 months
• Construction: 6-12 months

 

This site walks you through each part of the ADU process, from learning the rules and gathering initial inspiration through construction.

We recommend starting with two things:

• Use our ADU Wizard by putting in your address and seeing what’s possible.
• Read our ADU Rules page and then walk through the pages of this site one-by-one for a detailed guide on what to do next.