Accessory Apartments: An Affordable Housing Strategy

Affordable housing can often present a challenge for communities. How can a Town expand their affordable housing choices in a way that balances community needs with community character? How can a Town create affordable options to keep people in the community as they age or to accommodate changing lifestyles and housing needs? How can people more easily stay in their homes longer as children move out and/or income changes? How can a Town support affordable housing without building new developments? 

The Solution: Accessory Apartments 

Accessory apartments can help address these community challenges. Nationwide, one-third of single family homes have enough surplus space to accommodate an accessory apartment. In a relatively low-impact way, communities can expand their affordable housing choices. 

An accessory apartment, also know as an “accessory dwelling unit” (ADU), “granny flat” or “secondary unit”, is a self-contained second living unit built into or attached to an existing single family dwelling. It has its own kitchen, bathroom, and entrance. Sometimes, depending on the local ordinance, accessory apartments are built as detached units, such as cottages, guest houses, or in a converted garage or barn. 

An accessory dwelling unit is smaller than the main unit, similar in architectural styling, and meant to maintain the character of the existing neighborhood. In some cases, the unit is used for a relative or caretaker, providing more privacy than would be possible in the main house. In other cases, the unit is rented out to provide additional income to the house owner. 

Advantages of Accessory Apartments 

Provides affordable housing while preserving community character and saving tax dollars. Accessory dwelling units provide often needed affordable housing, thus helping a community accommodate a diversity of residents. At the same time, dispersing affordable housing within single family homes can provide desirable affordable housing while maintaining a family neighborhood culture. Local planning review can ensure that new units will fit with the character of the neighborhood. On the financial side, a town can add new housing units without having to provide utility infrastructure for a whole new development. 

Allows the elderly to live independently. Renting out a unit to a caretaker or young adult can provide the assistance and/or extra income it takes to allow an aging person to stay in their home. This choice can help the elderly remain independent and is usually much less disruptive for them. Or, an accessory apartment can be used for an elderly family member, to help maintain their independence, and often can reduce the cost of caring for them. 

Creates neighborhood diversity and stability. Providing housing options within a neighborhood ensures that people can stay in the neighborhood as they move through different stages in life. A young family can buy a house and rent out the accessory unit to help cover the mortgage. While raising children, they can use the unit for an aging relative, or as an extra room for guests. Later in life, they can rent out the apartment to a tenant or caretaker or move into it themselves. Accessory apartments provide options that help create diversity and stability. 

Makes efficient use of existing housing. Sprawl in Maine has been more a function of our population spreading out than of our population growing. Many people moved out to the suburbs to raise a family, but once their children are grown, they end up living in a house with more capacity than they need. Accessory apartments make use of the extra space while providing private living quarters. 

Provides supplemental income. With the choice of renting out a unit for extra income, it’s easier for homeowners to stay in their homes as they age and be able to continue paying the costs of a mortgage, utilities, maintenance, and real estate taxes. 

How to Make Accessory Apartments Work in Your Community 

A growing number of communities have had success with accessory apartments. Many Maine communities have amended their zoning ordinances to allow accessory dwelling units, recognizing the benefits of this housing option. Communities have addressed residents concerns such as accessory apartment units will alter the look of the neighborhood, or that the neighborhood will become more transient, or that there will be more traffic. Over 20 communities now have ordinance provisions for accessory dwelling units. An overview of Maine municipal ordinances with accessory dwelling unit provisions can be found on the GrowSmart website at 

As the ordinance provisions demonstrate, some of the key elements for a community to consider in an accessory dwelling unit provision are: 

  • Occupancy – owner occupancy of property required? Limit # of occupants in accessory unit? 
  • Size – size limit? Make size a % of single family dwelling unit size? 
  • Attached to or within single family dwelling only? Or also allow detached units? 
  • Parking – # of parking spaces and location 
  • Design standards – some degree of standards to ensure neighborhood compatibility?
While local ordinance provisions share some similarities, as you might expect, they also vary. Some communities limit occupancy to relatives, while some allow for rental units to non-family members. Some allow seasonal or short-term rental; some do not. An important part of making accessory apartments an option in your community is identifying the particular housing needs, the potential for accessory apartments to help address the needs, and identifying the concerns. Then a community can craft a provision that best addresses its particular circumstances. 

Community strategy and partnerships 

While accessory apartments are more common now than in the past, there is still hesitation in some communities. Towns that want to actively encourage the addition of accessory units may be more successful if they publicize their strategy. A public process also plants the idea in the minds of people who may be thinking of their own retirement or that of their aging parents. 

Partnering with community organizations can also help educate the public and facilitate the process of finding people who would benefit from adding an accessory unit to their home. A community network can provide information and referrals for trustworthy contractors, and help provide matching services between homeowners and renters. Neighborhood associations, churches, agencies on aging and housing, and transportation providers would all make good partners in this process. 

If your community is looking for affordable housing strategies, accessory apartments can provide a reasonable and workable approach – good for homeowners and your community. 


  • Accessory Dwelling Units. American Planning Association. QuickNotes
  • American Association of Retired Persons (AARP). Model ordinances for accessory dwelling units.
  • Maine AARP – Making Maine More Livable
  • “Community-Based Housing for the Elderly” American Planning Association. Planning Advisory Service Report (PAS) # 420
  • Rural By Design, Planning for Town and Country, Second Edition, by Randall Arendt. Accessory Dwelling Units: A Hidden Resource (pg.119) 

This article was originally published on Feb. 15, 2016. It is part of the GrowSmart Maine Educational Briefs series. Please visit their website to see the other "briefs" on smart growth planning topics

Written by

Lynne Seeley

Lynne Seeley is a Planning Consultant based in Yarmouth, Maine. She serves on the MAP board as Vice President and Communications Editor. Lynne is also on the board of GrowSmart Maine.