Wash. Rev. Code § 35.80.010
It is hereby found that there exist, in the various municipalities and counties of the state, dwellings which are unfit for human habitation, and buildings, structures, and premises or portions thereof which are unfit for other uses due to dilapidation, disrepair, structural defects, defects increasing the hazards of fire, accidents, or other calamities, inadequate ventilation and uncleanliness, inadequate light or sanitary facilities, inadequate drainage, overcrowding, or due to other conditions which are inimical to the health and welfare of the residents of such municipalities and counties.
It is further found and declared that the powers conferred by this chapter are for public uses and purposes for which public money may be expended, and that the necessity of the public interest for the enactment of this law is hereby declared to be a matter of local legislative determination.
RCW 35.80.010