Wash. Rev. Code § 47.20.620
If, in any condemnation proceeding authorized herein, it appears that there is any building wholly or partially upon any of the real estate to be taken, the jury, or the court, if the jury be waived, shall add to the value of the land taken the amount of damages to the building. If the entire building is taken, or if the building is damaged so that it cannot be readjusted to the real estate not taken, then the measure of damages shall be the fair cash value of the building. If part of a building is taken or damaged and the building can be readjusted or replaced on the real estate remaining, then the measure of damages shall be the cost of readjusting or moving the building, or part thereof left, together with the depreciation in the market value of said building by reason of said readjustment or moving.
RCW 47.20.620