The bill authorizes counties in Washington State to incorporate middle housing types into their development regulations within unincorporated urban growth areas, certain limited areas of more intensive rural development, and fully contained communities. Specifically, it allows counties to permit up to four residential units per lot in these designated areas, ensuring that the standards for middle housing are not more restrictive than those for detached single-family residences. The bill mandates that middle housing must be served by existing sewer services in rural development areas and by both water and sewer services in urban growth areas.

Additionally, the bill includes provisions that exempt the adoption of ordinances and development regulations related to middle housing from administrative or judicial appeals, thereby streamlining the process for counties to implement these changes. It also reenacts and amends existing laws to clarify that actions taken to implement the new middle housing regulations are not subject to appeals, ensuring a more efficient pathway for local governments to enhance housing availability.