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Accessory Dwelling Units Model State Act and Local Ordinance Skip to content

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Creating Room for Accessory Dwelling Units

An AARP and APA model for state and local acts and ordinances helped pave the way

Drawing of a large house and smaller house attached to its side.

The cover image from "Accessory Dwelling Units: Model State Act and Local Ordinance."


More About ADUs

The ABCs of ADUs

Visit AARP.org/ADU to learn more about ADUs and download or order AARP's free ADU publications.

EDITOR'S NOTE: Zoning ordinances that prohibit ADUs or make it extremely difficult for homeowners to create them are the principle obstacle to the wide availability of this housing option.

The following article introduces Accessory Dwelling Units: Model State Act and Local Ordinance, a report developed in 2000 by AARP and the American Planning Association to assist interested citizens, planners and government officials in evaluating potential changes to state and local laws in order to encourage the wider availability of ADUs. This sample legislation was drafted to meet the needs of a broad range of communities. Optional provisions, including those attractive to very cautious communities, are incorporated in the model ordinance to provide as many choices as possible for jurisdictions to consider.

In the year's since the report's publication two-decades ago, many communities have adopted ADU-friendly policies. AARP is providing updated resources as the momentum grows for ADUs. Visit AARP.org/ADU for more current information and resources about accessory dwelling units.

 — AARP Livable Communities (May 2019)


Sometimes known as accessory apartments, mother-in-law suites or "granny flats," Accessory Dwelling Units (ADUs) provide more housing options in existing neighborhoods by allowing homeowners to build additional units on their lots.

Accessory Dwelling Unit or ADU is a catch-all term for all of these situations — whether the unit is attached to an existing home or placed elsewhere on the property, such as over a detached garage or as a stand-alone structure in the backyard. ADUs are among the housing options that help to ensure that people of all ages, including older adults, have a roof over their heads. 

For an older person with a declining incomes and growing housing affordability challenges, renting out a unit or moving a friend or relative onto their property can help with those costs.

AARP's housing philosophy and related public policies (which can be found in Chapter 9 of the AARP Policy Book), encourage states and localities to look to the model act and create legislation and zoning policies that support ADUs.

For any town, city or county considering a plan to broaden the implementation of ADUs, it's important to:

  1. Anticipate the potential fears of residents and local officials about matters such as increased traffic, parking issues and neighborhood changes.

  2. Do research about the regulations that have been put in place in other communities. The good examples address community concerns, maximize the freedom of property owners and provide a needed source of housing options.

  3. Understand that each ADU effort is different because locations and people are different. This is an area where a one-size-fits-all policy will not work.

  4. Since ADUs require making a change that is literally in someone's backyard, opinions can be strong and the policy work can easily become political. Planners and politicians who go into a community meeting on the issue must do their homework and know what to expect. Concerns about parking, fire safety, neighborhood character and the future uses of the ADUs should be anticipated and addressed. Those concerns also need to be weighed against the need for housing options in the community for people of all ages and the rights of landowners who want some flexibility about how to use their property.

The reward for a community that implements ADUs successfully is a range of new housing options. In places where housing affordability or the opportunities to age-in-place are limited, ADUs can positively impact many families.

Rodney Harrell, PhD., is the director of Livability Thought Leadership for the AARP Public Policy Institute. This article is adapted from one published on his blog, DrUrbanPolicy. Follow him on Twitter at @DrUrbanPolicy.

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