RCW 91.08.170

The jury or court shall also ascertain the just compensation to be paid to any person found to have an interest in any lot or parcel of land or property which may be taken or damaged for such improvement, whether or not such person's name or such lot or parcel of land or other property is mentioned or described in said petition: PROVIDED, That such person shall first be admitted as a party defendant to such suit by such court and shall file a statement of his or her interest in, and a description of, the lot or parcel of land or other property in respect to which he or she claims compensation.