If a court or arbitrator determines a defective condition as described in RCW 59.18.060 to be so substantial that it is unfeasible for the landlord to remedy the defect within the time allotted by RCW 59.18.070, and that the tenant should not remain in the dwelling unit in its defective condition, the court or arbitrator may authorize the termination of the tenancy: PROVIDED, That the court or arbitrator shall set a reasonable time for the tenant to vacate the premises.