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Accessory Dwelling Unit (ADU) Ordinance

An Accessory Dwelling Unit (ADU) is a small, separate living unit built on the same lot as a single-family home. Traditionally, ADUs can be an addition to a single-family home, a conversion of a basement or attached / detached garage or outbuilding, or a new freestanding detached structure. An ADU has all the basic facilities for day-to-day living, such as a kitchen, sleeping area, and bathroom. As the term "accessory" implies, ADUs are smaller in size, use and prominence than the main residence on the lot.

On December 15, 2020 the Board of County Commissioners adopted the rural accessory dwelling unit (ADU) ordinance for all rural unincorporated areas of Thurston County. This ordinance will join the Urban Grown Areas (UGAs) of Olympia, Lacey, Tumwater, and Grand Mound, as well as the cities in allowing ADUs.

The following links will redirect you to the respective ordinances for each jurisdiction.

Frequently Asked Questions
Accessory Dwelling Unit (ADU) FAQ

Contact Us
Thurston County Building Development Center, 2000 Lakeridge Drive SW, Olympia, WA 98502-6045. Phone: (360) 786-5490. TTY/TDD call 711 or 1-800-833-6388 E-mail: permit@co.thurston.wa.us.

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