ADU Guidance Update

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Project Background:

Until 2021, the GMA required that many counties, and any city over 20,000 population allow accessory dwelling units (ADUs). RCW 43.63A.215 required that a report and model ordinance be developed, included as Appendix A MRSC’s “Accessory Dwelling Units: Issues and Options.”

In 2021, HB 1220 substantially increased the text of the housing element requirements in RCW 36.70A.070(2), requiring ALL local governments planning under the GMA to consider the role of accessory dwelling units in meeting housing needs as they make adequate provisions for existing and projected needs of all economic segments of the community

In response to this new language, and to address the critical need to address housing supply and affordability, Commerce is updating the 1994 ADU guidance with separate recommendations for cities and for counties, as the issues are significantly different. With input from stakeholders, industry experts, and a review of best practices, the new guidance will include recommendations and examples of development regulations, design, and research related to finance, landlord education and messaging, and other resources to reduce barriers to ADU development. Resources will include:

  • Recommended approach for cities for design, size, and other factors related to the development of ADUs, that provides best practices for local governments, and may include considerations related to parking, size, design, use as short term rentals, affordability incentives, or other tools to encourage the development, placement and affordability of ADUs.
  • Recommended approach for counties, which may include factors such as rural character, use for family, farmworkers or as short term rentals, and considerations in LAMIRDS and unincorporated urban growth areas to consider the need for affordable housing, to address GMA requirements for rural and resource lands.
  • Sample presentations and editable handouts for local government staff to use as they work on local ADU ordinances.
  • Recorded webinars to train local government staff planners on the ADU recommended policies, one for cities, and one for counties, while also considering messages for local planning commissioners and elected officials.

 Project Timeline:

  • 2022-2023: Stakeholder engagement conducted throughout project duration
  • Winter 2022-2023: Draft ADU recommendations for cities and counties
  • Spring 2023: Education and training materials for cities and counties to promote and implement ADU programs and Final ADU recommendations for cities and counties
  • Summer 2023: Presentations and training webinars held to roll out the new guidance

For more information, please contact Catherine McCoy, Senior Planner,, work cell 360.280.3147; or Anne Fritzel, Housing Programs Manager,, work cell 360-259-2525.


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