ADU Regulations in Maine: The Complete Guide

Accessory Dwelling Units (ADUs) have become a popular way to add extra living space, create rental opportunities, or provide housing for family members. If you’re a Maine property owner wondering about the rules for ADUs, you’re in the right place. This guide breaks down everything you need to know about ADUs in Maine, from new laws to building options like tiny homes, prefab units, and log cabins.

Are ADUs Allowed in Maine?

Yes! Accessory Dwelling Units are allowed across the state of Maine. In fact, Maine passed legislation to make it easier for homeowners to add an ADU to their property. While local cities and towns still have the ability to shape specific details like design and size requirements, state law now guarantees that most single-family homeowners can build at least one ADU by right.

This means you won’t necessarily need a special permit or zoning change, but you will still need to meet local building codes and planning regulations.

What is the New Law in Maine for ADUs?

In 2022, Maine passed LD 2003, a law aimed at addressing the state’s housing shortage by promoting the construction of ADUs and other types of flexible housing. Under LD 2003:

• Single-family homes are allowed to add one ADU per lot.
• ADUs can be attached (like a basement apartment) or detached (like a backyard cottage).
• Cities and towns must permit ADUs by right in most residential areas.
• Some local zoning restrictions, like lot size minimums or parking requirements, have been relaxed to encourage more ADUs.

However, municipalities can still impose reasonable design standards and placement rules, so checking with your town before starting construction is essential.

Can I Build Another House on My Property in Maine?

If you’re thinking about adding a full-size second home to your property, that’s a little trickier. An ADU is meant to be a smaller, secondary living space, not a completely separate house. If you want to build another full house, you might need to meet different zoning requirements, subdivide your land, or apply for special approvals.

For most people, building an ADU is the faster, easier option if you’re looking for extra living space without a big hassle.

ADUs That Are Allowed in Maine

Most Maine areas require ADUs to fall somewhere between 200 and 1,000 square feet. Below are all our ADU models that fall within this range. Explore the options below or contact us; we’d happily help you find the perfect ADU for your property.

 

What Is Considered An ADU in Maine?

In Maine, an ADU is considered a smaller living space built on the same lot as your main house. It must be independent, meaning it should have its own kitchen, bathroom, and sleeping area. It should also be smaller than the primary home and have a separate entrance.

ADUs can come in all shapes and styles: a finished basement, a garage apartment, a tiny backyard cottage, or even a brand-new detached unit. If you’re curious about what your ADU could look like, contact Zook Cabins. We would be happy to walk you through the possibilities.

What is considered an ADU often varies from place to place within Maine. Please check with your local planning, zoning, or building department to make sure your ADU plans comply with local requirements.

Can Park Model Tiny Homes Be Used As ADUs?

Some towns in Maine may allow a park-model tiny home to be used as an ADU, especially if it’s permanently placed and meets residential safety standards. Others allow them more broadly, while some prohibit them entirely. Because park models are typically built to RV standards rather than residential codes, they can pose challenges when used as permanent dwellings. Before purchasing a tiny home, contact your local code enforcement office to confirm what’s allowed.

Below are some park models that fall within the square footage range permitted in most parts of Maine. Check out our comprehensive guide for clarification on whether park model tiny homes are allowed in the state.

Can Log Cabins Be Used As An ADU?

Definitely! In fact, a log cabin fits right in with Maine’s character and charm. Our log cabins make a perfect ADU if they meet local building codes and zoning rules.

Your log cabin ADU will need basics like a kitchen, bathroom, and bedroom, and it’ll need to be hooked up properly to utilities. A log cabin can qualify as an ADU if it meets the minimum size standard of 190 square feet, is placed on a property with a single-family home, and does not exceed the maximum size outlined by your locality. It must also meet any local design or setback requirements, just like any other structure.

Can Modern Cabins Be Used As ADUs?

Yes, our Modern Cabins can be used as ADUs if they meet your local sizing and placement requirements. 

In Maine, most ADUs can be no larger than 800-1,000 square feet. Below, we’ve compiled some of our models that fall within this range.

What is the Difference Between a Prefab ADU & a Modular ADU?

The main difference between a prefab & modular ADU is this:

• A prefab ADU is any unit that’s built completely off-site and then delivered to your location fully assembled. 
• A modular ADU is built in sections off-site but assembled on-site.

The chart below provides a closer look at the features that differentiate the two.

Feature	Prefab ADU	Modular ADU
Built to Full Residential Code	Not always	Yes
Permitting Ease	Depends on local codes	Usually easier
Built Off-Site	Yes	Yes
Assembled On-Site	Yes	Yes
Delivered Fully or in Parts	Yes (fully built or panels)	Large modules

Both options save a ton of time compared to traditional building. Modular homes, though, usually have to meet the same codes as stick-built houses, making permitting easier.

To better understand the differences between the two, check out our clear-cut guide on prefab and modular ADUs.

Size & Placement Requirements for ADUs in Florida

Every town in Maine can set its own size and placement rules for ADUs, but there are some common trends. Typically, an ADU must be smaller than the main house, often limited to around 800 to 1,000 square feet. Placement rules might require the unit to be behind the primary home, have its own entrance, and meet setback requirements (how far it sits from property lines).

Some towns also limit the height of detached ADUs or require that they “blend in” with the main house by using similar materials and colors.

What is the Minimum Size for an Accessory Dwelling Unit?

In Maine, the minimum size for an ADU is typically between 190 to 200 square feet. 

This ensures that the unit provides enough space for basic living needs like sleeping, cooking, and using the bathroom. Keep in mind, though, local rules can differ slightly, so you’ll want to double-check with your town’s building department.

If your ADU cannot be larger than 400 square feet, our ADUs will not be able to accommodate your needs. However, if park models are allowed in your area, they can be an excellent fit for your needs.

Can My ADU Be Bigger Than My House?

In most cases,  your ADU can’t be larger than your primary home. Maine’s ADU regulations usually require the unit to be a secondary, smaller living space. Some towns cap the ADU at 50% to 75% of the size of the main home. So if your house is 2,000 square feet, your ADU might be limited to somewhere between 1,000 and 1,500 square feet.

If you’re planning a smaller main home with a larger ADU, you might have to look into special permits or variances, but it’s not the typical setup.

How Close To My House Can I Build An ADU?

In many parts of Maine, you’ll need to leave a gap of at least 10 to 20 feet between structures. 

However, the exact distance between your main home and your ADU, often called a setback, varies depending on your local zoning regulations. Some towns might require even more space, especially if you’re installing a new septic system or connecting to utilities. Again, checking in with your local planning office is key to getting this detail right.

Do You Need A Permit For An ADU in Maine?

You’ll almost always need a permit before building an ADU in Maine. Even though state law (thanks to LD 2003) makes it easier to add an ADU, your project still has to meet building codes and local regulations. That means filing the proper paperwork, getting approval from your city or town, and making sure your structure is up to safety standards. Skipping the permit process could lead to fines or being forced to tear down your new space, not worth the risk!

Are There Any Incentives or Grants for ADUs in Maine?

Currently, Maine doesn’t have a statewide grant program specifically for ADUs. However, because ADUs help expand affordable housing options, some towns and cities are starting to offer local incentives. 

Sometimes, homeowners might get help with permitting fees, reduced impact fees, or access to financing programs designed to boost housing supply. It’s worth checking with your local housing authority or planning office to see if there are any programs you could tap into.

What Features Are Included in an ADU from Zook Cabins?

Exact features vary by model, but all of our ADUs feature an array of designs and floor plans, so it’s easy to find the best fit for your needs.

Since our ADUs are designed to be turnkey, meaning they come equipped with everything you need for comfortable living, all our models include:

• Full kitchens with cabinets and appliances
  
• Bathrooms with showers or tubs
  
• Living areas with plenty of natural light
  
• Heating and cooling options
  
• Insulation that handles Maine’s cold winters
  
• Options for front porches, loft spaces, and extra bedrooms
  

Certain features like cabinets, countertops, and tile work can be customized. Reach out to one of our sales representatives to explore your options.

Are Zook Cabin’s ADUs Built to Code?

Yes! Our models were specifically designed with local size and room requirements in mind. Since these are modular homes, you’ll need to install a permanent foundation to ensure full compliance with local codes.

Each of our models ranges between 500 and 900 square feet, comfortably within the 200 to 1,000 square foot range common in Maine. They’re available in layouts with a single bedroom and bathroom or multiple bedrooms and bathrooms. If you need help determining which foundation is best for your ADU, contact us and we’ll be happy to help.

Can an ADU Have Multiple Bedrooms and Bathrooms?

Yes, an ADU can include more than one bedroom and bathroom. However, the number allowed often depends on the unit’s size, zoning regulations, and local rules. While every ADU must have at least one bedroom and one bathroom, many designs, particularly on larger lots or for those looking to increase rental potential, feature two or even three bedrooms and multiple bathrooms.

Our Grove, Luna, and A-Frame models all feature one to two bedrooms and bathrooms. If your area only allows one bedroom and bathroom, the Sonoma ADU includes one. Browse our models to find the one that meets your locality’s requirements.

Are ADUs A Good Investment?

Yes! ADUs can serve as excellent rental properties and, in some cases, may even be sold separately from the primary residence. Additionally, some areas offer grants or reduced permitting fees, providing an extra financial incentive to add one to your property. Contact your local officials to learn more about the options available in your area.

What Are The Requirements For ADUs In Each County in Maine?

With few counties in the state, most regulations and requirements for Accessory Dwelling Units (ADUs) are the responsibility of city and town officials within each county. For those who reside in unincorporated parts of each of the 16 counties in Maine, we’ve compiled a list of the county officials to contact about whether or not you can have an ADU on your property.

If you live within the authority of a city or town official, we recommend that you skip this list to find out if your city or town allows ADUs.

County	Contact	Allows ADUs?	Min Sq. Ft.	Max Sq. Ft.
Androscoggin County	Planning	Yes	Unspecified	1,000
Aroostook County	Land Use Planning Commission	Yes	Unspecified	800–1,000
Cumberland County	Community Development	Yes	Unspecified	1,000
Franklin County	Land Use Planning Commission	Yes	Unspecified	1,000
Hancock County	Planning Commission	Yes	Unspecified	1,000

What are the Requirements for an ADU in Androscoggin County?

In Androscoggin County, ADU approval generally depends on the municipality you live in. Unincorporated areas may allow ADUs if they follow the basic size guidelines,  usually not exceeding 1,000 square feet. Structures like tiny homes, log cabins, or modular buildings can often be used if they meet residential code standards.

What are the Requirements for an ADU in Aroostook County?

For Aroostook County’s unincorporated areas, ADUs are generally permitted, but units must stay smaller than the primary home. Sizing is often capped around 800–1,000 square feet. Prefab cabins, tiny homes on foundations, and traditional site-built ADUs are acceptable if they meet local standards.

What are the Requirements for an ADU in Cumberland County?

In Cumberland County, where many towns set their own rules, ADUs are allowed in most areas. If you’re outside of city limits, ADUs must follow general guidelines, usually less than 1,000 square feet. Modular homes, tiny houses on foundations, and small cabins can qualify.

What are the Requirements for an ADU in Franklin County?

Franklin County’s rural areas often allow ADUs that are under 1,000 square feet and compliant with basic building codes. Log cabins, small modular homes, and properly permitted tiny homes are common ADU options.

What are the Requirements for an ADU in Hancock County?

In Hancock County, ADUs are typically allowed in rural zones if they meet size and setback requirements. ADUs must be smaller than the main dwelling, usually no larger than 1,000 square feet. Log cabins, panelized builds, and modular units are good ADU choices.

What Counties in Maine Have Unclear ADU Requirements?

The following counties do not have clearly defined ADU regulations. In many cases, these decisions are handled by local officials within the county. You can skip this section and review the rules specific to your city or town.

Kennebec County	Kennebec County
Knox County	Knox County Courthouse
Lincoln County	Regional Planning
Oxford County	County Commissioner
Penobscot County	Commissioner
Piscataquis County	County Commissioner’s Office
Sagadahoc County	County Courthouse
Somerset County	County Commissioner
Waldo County	Commissioners Office
Washington County	County Commissioners
York County	County Commissioners

Find Your Accessory Dwelling Unit Requirements in Maine By Municipality

City	Contact	Allows ADUs?	Min Sq. Ft.	Max Sq. Ft.
Portland	Planning & Development Department	Yes	Unspecified	⅔ of principal structure/no larger than principal structure
Lewiston	Planning & Code Enforcement	Yes	190	900
Bangor	Planning Department	Yes	190	50% of the principal dwelling or 1,000 square feet, whichever is less
South Portland	Code Enforcement	Yes	190	1,200 or 90% of primary
Auburn	Planning, Permitting, & Code	Yes	Unspecified	Unspecified
Scarborough	Planning & Codes Department	Yes	190	Up to 1,500 depending on primary
Sanford	Planning & Development Department	Yes	Unspecified	1,000 or 40% of primary
Biddeford	Planning & Development Department	Yes	300	900 or 35% of primary
Saco	Code Enforcement Department	Yes	400	1,000
Westbrook	Planning Department	Yes	190	800

What are the Requirements for an ADU in Portland, Maine?

Portland permits ADUs so long as they meet the following requirements:

• Maximum Size: 
  • Attached ADU: ⅔ of the gross floor area of the largest principal unit on the lot
  • Detached ADU: Shall not exceed the gross floor area of the principal structure
• Number Per Lot: 2
• Setbacks: Not permitted between principal structure and front lot line, side & rear setbacks must adhere to the requirements for detached accessory structures

To ensure compliance with all applicable requirements, specifically those that vary by zoning, contact the Planning & Development Department.

What are the Requirements for an ADU in Lewiston, Maine?

Lewiston, Maine, outlines the following requirements for accessory dwelling units:

• Minimum Size: 190 square feet
• Maximum Size: 900 square feet
• Max. Number of Bedrooms: 2
• Owner-Occupancy: Required
• Number Per Lot: 1

If you have any questions about ADU requirements in Lewiston or to confirm compliance with applicable regulations, contact the Planning & Code Enforcement Department.

What are the Requirements for an ADU in Bangor, Maine?

The requirements for ADUs in Bangor are as follows:

• Minimum Size: 190 square feet
• Maximum Size: 50% of the square footage of the principal unit or 1,000 square feet, whichever is less
• Setbacks: Same as principal unit
• Number Per Lot: 1

To certify compliance with all applicable regulations, contact the Bangor Planning Department.

What are the requirements for an ADU in South Portland, Maine?

In South Portland, to construct an ADU you must meet the following requirements:

• Minimum Size: 190 square feet
• Maximum Size: 800 square feet or 90% of the primary building’s living area, whichever is less
  • ADUs can be up to 1,200 square feet on larger lots, but still no more than 90% of the primary structures living area
• Owner-Occupancy: Required
• Can Be Sold Separately: No

Exact requirements vary by your property’s zoning designation, especially if you reside in a special shoreline zone. To confirm compliance with all applicable regulations contact Code Enforcement.

What are the requirements for an ADU in Auburn, Maine?

Auburn does allow ADUs, but the exact requirements regarding size, placement, and owner-occupancy are unclear. Contact the Planning, Permitting, and Codes Office for clarification on what is allowed. 

What are the requirements for an ADU in Scarborough, Maine?

In Scarborough, Maine, homeowners are permitted to build an accessory dwelling unit either within, attached to, or detached from their main home, so long as they meet the following requirements:

• Number Per Lot: 1
• Owner-Occupancy: Required 
• Short-term Rentals: Not allowed
• Number of Occupants: 2
• Minimum Size: 190 square feet
• Maximum Size: Depends on:

If the living space of the single-family dwelling is:	The living space of the ADU shall not exceed:
Under 2,000 square feet	40% of primary structure or 750 square feet, whichever is greater
2,000-3,000 square feet	35% of the primary dwelling or 750 square feet, whichever is greater
3,000-5,000 square feet	30% of the primary dwelling or 1,050 square feet, whichever is greater
5,000 square feet or more	20% of the primary dwelling or 1,500 square feet, whichever is greater

• Setbacks: 100 feet from the primary dwelling

Additional requirements apply. Contact the Scarborough Planning & Codes Department to ensure compliance with all applicable regulations.

What are the requirements for an ADU in Sanford, Maine?

The requirements for ADUs in Sanford are as follows:

• Number Per Lot: 1
  • Unless located in the city’s Growth Zone, in which case 2 are permitted
• Maximum Size: 40% of the living area of the main home or 1,000 square feet, whichever is greater
• Maximum Number of Bedrooms: 3
• Owner-Occupancy: Required

To certify compliance with all applicable regulations, contact the Sanford Planning & Development Department.

What are the requirements for an ADU in Biddeford, Maine?

In Biddeford, Maine, homeowners can add one accessory dwelling unit per residentially zoned lot, provided they meet these specific conditions:

• Owner-Occupancy: Required
• Minimum Size: 300 square feet
• Maximum Size: 35% of the primary home’s floor area or 900 square feet, whichever is greater
• Number of Bedrooms: 2
• Max. Number of ADU Residents: 3

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Detached ADUs must include at least 10% window coverage on any façade facing a street or alley, while attached and internal ADUs must not add new entrances facing the street, and stairways must be enclosed. Only one off-street parking space is required unless there is public or legal on-street parking within 1,000 feet. 

Additional rules apply to ensure that detached ADUs fit the residential character, including the use of finished railings for any external stairs. Creating an ADU also requires a $200 non-refundable application fee, along with the necessary building permits, and no unit can be occupied until a certificate of occupancy is issued. 

ADUs in Biddeford must comply with all local, state, and federal regulations, and any modifications to improve accessibility for disabled residents may be approved by the Code Enforcement Office.

What are the requirements for an ADU in Saco, Maine?

If you’re considering building an accessory dwelling unit in Saco, Maine, there are a few key requirements you must meet:

• Number of ADUs Per Property: 1
• Sizing Requirements: Between 400-1,000 square feet
• Permanent Foundation: Required
• Setbacks & Placement: Same as primary structure, based on zoning district

Before you start building or converting, you’ll need to get a building permit or a certificate of occupancy from the city. Saco’s Code Enforcement Office handles all the approvals and can help answer any questions if you get stuck along the way.

What are the requirements for an ADU in Westbrook, Maine?

The requirements for ADUs in Westbrook are as follows:

• Number of ADUs Per Lot: 1
• Minimum Size: 190 square feet
• Maximum Size: 800 square feet
• Minimum Ceiling Height: 7 feet
• Owner-Occupancy: Required
• Can be Sold Separately: No

Before you start construction, you’ll need a building permit and a certificate of occupancy from Westbrook’s Code Enforcement Office. And keep in mind: if the city creates short-term rental rules later, your ADU would have to follow them too. Overall, it’s a great way to add living space, help family members stay close, or create a little extra rental income, just make sure you follow the steps!

Searching For An ADU Builder Serving Maine?

As you’ve learned in this article, modular ADUs offer a more efficient approach to adding a secondary unit, since they’re built off-site and assembled quickly on your property. They’re also generally easier to permit than traditional site-built structures. If you’re searching for an ADU builder that will ensure compliance with local codes, you’re in the right place.

Our ADU models range from 571 to 800 square feet, comfortably within the typical 200 to 1,000 square foot range allowed across the state of Maine. Each model offers a variety of bedroom and bathroom configurations to accommodate your household needs or meet local occupancy requirements.

With a range of designs, you’re sure to find the ADU that best matches your property. If its style doesn’t quite fit, our park models, log cabins, or modern cabins, provided they meet local sizing requirements, could be the perfect alternative.

Tiny Home & ADU Rules By State: How Do They Compare?

In some parts of the U.S., park model tiny homes can be used as ADUs, while in others, they can’t. The rules for these two types of structures may be nearly identical in one area but completely different in another.

Because regulations vary not just by state but also between neighboring cities and towns, it’s important to understand what’s allowed where you live.

Check out the chart below to see how different states approach park model tiny homes and ADUs, and where the two overlap—or diverge.