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ADU Model State Act and Local Ordinance

This new, free AARP publication can be used by state and local legislators to establish policies that encourage the creation of accessory dwelling units

AARP supports the wider availability of accessory dwelling units, or ADUs, as an affordable, accessible housing option for people of all ages.

That's why, late in the last century, the AARP Public Policy Institute asked the American Planning Association to develop model legislation — specifically, a state statute and a local ordinance — as a resource to assist AARP volunteer leaders and other interested residents, planners and government officials in evaluating potential changes in state laws and local zoning codes. 

ADU Publications from AARP

The following resources and more can be found at AARP.org/ADUs.


ADU Model State Act and Local Ordinance

From AARP State Advocacy & Strategy Integration, Government Affairs

Accessory Dwelling Units Model State Act and Local Ordinance (56 pages)


The ABCs of ADUs

From AARP Livable Communities

The ABCs of ADUs: A Guide to Accessory Dwelling Units and How They Expand Housing Options for People of All Ages (20 pages)


Accessory Dwelling Units

From the AARP Public Policy Institute

Accessory Dwelling Units: A Step by Step Guide to Design and Development (113 pages)

That resource was called Accessory Dwelling Units: Model State Act and Local Ordinance. (The new version is available by clicking the linked title as well as by viewing and/or downloading the PDF at the end of this page.)

When AARP issued its 2000 edition of the model state act and local ordinance, only Washington State had legislation requiring local governments to authorize ADUs. Since then, many states have adopted legislation preempting local prohibitions to one degree or another, usually for larger cities and towns. Legislation has been enacted in California (2016), New Hampshire (2017), Oregon (2017), Rhode Island (2017) and Vermont (2005).

In parallel with local governments’ continuing revisions to their ADU ordinances, California (2019), Oregon (2019) and Vermont (2020) passed many amendments to their initial ADU legislation, chipping away at the various local regulatory barriers to ADU construction. Legislation authorizing or encouraging local governments to authorize ADUs was passed in Florida (allowing ADUs as affordable housing, 2004) and Maine (2019). Hawaii has had legislation allowing counties to permit two dwellings on all single-family lots since 1981.

The continuing demand for, and evolving experience with ADU legislation, spurred AARP to prepare a new version of the model state act and local ordinance. This updated resource — available as a 56-page downloadable PDF — is organized into three sections:

Table of Contents

  1. About Accessory Dwelling Units
    An overview of what ADUs are and why they are so needed.

  2. Model State ADU Act
    Two policies are presented in this section. The first is the “Optimal” state act, which limits local governments from prohibiting or discouraging the creation of ADUs. The second, referred to as the “Minimal” version, which grants local governments with the full range of authority to permit and regulate ADUs.

  3. Model Local ADU Ordinance
    This model ordinance is designed for communities in places where state law allows for local ordinances authorizing and governing ADUs but does not impose any constraints on local governments. 

Page published January 2021

Accessory Dwelling Units Model State Act and Local Ordinance

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