The bill aims to authorize middle housing in unincorporated urban growth areas, certain limited areas of more intensive rural development, and fully contained communities in Washington State. It allows counties that are required or choose to plan under RCW 36.70A.040 to incorporate regulations for middle housing types on parcels that permit single-family residences. Specifically, it stipulates that counties may not authorize more than four residential units per lot and must ensure that development regulations for middle housing are not more restrictive than those for detached single-family residences. Additionally, middle housing must be served by sewer services in rural development areas and by both water and sewer services in urban growth areas.

The bill also 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. Furthermore, it amends existing laws to clarify that actions taken to implement the new middle housing regulations are not subject to appeals, ensuring that local governments can proceed with these housing initiatives without the risk of legal challenges. Overall, the bill seeks to enhance housing availability and promote diverse housing options in designated areas while maintaining certain regulatory standards.