Wash. Rev. Code § 35.70.010
For the purposes of this chapter all property having a frontage on the side or margin of any street shall be deemed abutting property, and such property shall be chargeable, as provided in this chapter, with all costs of construction of any form of sidewalk improvement, between the margin of the street, as defined by a curb or the edge of the traveled road surface, and the line where the public right-of-way meets the abutting property, and the term sidewalk as used in this chapter shall be construed to mean and include any and all pedestrian structures or forms of improvement for pedestrians included in the space between the street margin, as defined by a curb or the edge of the traveled road surface, and the line where the public right-of-way meets the abutting property.
RCW 35.70.010