Accessory Dwelling Unit Policy

Thurston County is working on a policy to allow a small, separate living unit on the same lot as a single-family home in rural, unincorporated parts of the County.  Design standards for these accessory dwelling units (ADUs) are being explored as part of the County's Comprehensive Plan Update. 

Generally, ADUs are:

  • Separate from the main home, and have all the basic facilities for day-to-day living like a kitchen, bathroom and sleeping area. 
  • Smaller in size than the main home on a lot, as the word "Accessory" implies.  
  • Attached to the main home; detached from it; or a part of an internal conversion, like a basement.

Thurston County currently does not allow ADUs in the rural county. However, ADUs are allowed within the urban growth areas (UGAs) of Olympia, Lacey and Tumwater. ADUs are also allowed in certain zones of the Grand Mound UGA. 

While Thurston County does not currently allow ADUs, the county does allow Family Member Units (FMUs). Currently, a FMU must be a temporary mobile/manufactured or modular home. Only family members may live in FMUs, and the the FMU must be removed once the family member leaves.

The proposed policy for ADUs would change design and development standards (i.e., setbacks, building height, etc.)

ADU Types‚Äč