603.8 Underground Ducts

Ducts shall be approved for underground installation. Metallic ducts not having an approved protective coating shall be completely encased in not less than 2 inches (51 mm) of concrete.

Ducts shall have a minimum slope of ¹/₈ inch per foot (10.4 mm/m) to allow drainage to a point provided with access.

Ducts shall be sealed, secured and tested prior to concrete encasement or direct burial. Ducts shall be leak tested as required by Section C403 of the International Energy Conservation Code.

Plastic ducts shall be constructed of PVC having a minimum pipe stiffness of 8 psi (55 kPa) at 5-percent deflection when tested in accordance with ASTM D2412. Plastic duct fittings shall be constructed of either PVC or high-density polyethylene. Plastic duct and fittings shall be utilized in underground installations only. The maximum design temperature for systems utilizing plastic duct and fittings shall be 150°F (66°C).