Wash. Rev. Code § 39.12.020
The hourly wages to be paid to laborers, workers, or mechanics, upon all public works and under all public building service maintenance contracts of the state or any county, municipality or political subdivision created by its laws, shall be not less than the prevailing rate of wage for an hour's work in the same trade or occupation in the locality within the state where such labor is performed. For a contract in excess of ten thousand dollars, a contractor required to pay the prevailing rate of wage shall post in a location readily visible to workers at the jobsite: PROVIDED, That on road construction, sewer line, pipeline, transmission line, street, or alley improvement projects for which no field office is needed or established, a contractor may post the prevailing rate of wage statement at the contractor's local office, gravel crushing, concrete, or asphalt batch plant as long as the contractor provides a copy of the wage statement to any employee on request:
This chapter shall not apply to workers or other persons regularly employed by the state, or any county, municipality, or political subdivision created by its laws.
RCW 39.12.020