Wash. Rev. Code § 64.55.150 (2026)

Upon the demand of a party to an arbitration demanded under RCW 64.55.100, any subcontractor or supplier against whom such party has a legal claim and whose work or performance on the building in question becomes an issue in the arbitration may be joined in and become a party to the arbitration. However, joinder of such parties shall not be allowed if such joinder would require the arbitration hearing date to be continued beyond the date established pursuant to RCW 64.55.100, unless the existing parties to the arbitration agree otherwise. Nothing in RCW 64.55.010 through 64.55.090 shall be construed to release, modify, or otherwise alleviate the liabilities or responsibilities that any party may have towards any other party, contractor, or subcontractor.