In addition to the requirements of the International Mechanical Code and the Washington State Energy Code air ducts for:

(1) An expandable or multiple commercial coach may have ducts of the heating system installed in the various units. The points of connection must be so designed and constructed that when the commercial coach is fully expanded or coupled, the resulting duct joint will conform to the requirements of this chapter.

(2) Installation instructions for supporting the crossover duct from the commercial coach must be provided for on-site installation. The duct must not touch the ground.