PVC Installation Guide – Underground Ducts
Install Above Water Table The PVC duct system is not designed to be waterproof. Installation must be made safely above the water table. Ducts should not be placed where water infiltration may occur.
The top of the duct can extend into the cement, leaving a minimum of 2 ½” of cement above the top, or the duct can be placed well below the cement. However, the duct should not be placed so deep that the weight on it will exceed the load capabilities.
Trenching and Backfill
After the excavation has been made, no special bedding need be used for PVC Duct. It can rest right on the ground, or be set in sand or light aggregate. Pea gravel or sand (or the material taken from the trench, if equivalent) can be used to backfill. Spread the backfill material evenly around the duct making sure there are no gaps, and tamping in place is a recommended practice. No cement is needed to fill in around the duct, since the tamped fill holds the duct in place and the plastic coating prevents ground corrosion of the galvanized steel. This plastic coating is resistant to any minerals or salts that may be in the backfill soil. PVC Duct will not “float” when backfilled to within 2” of the top of the duct. Concrete is then poured so that all “tie-down” work is eliminated.
CAUTION: When backfilling or grading, care should be taken not to dump or push heavy loads directly on the duct, nor should heavy equipment be allowed to run over the duct. It can be crushed under thoughtless abuse.
Large Diameter Ducts
Special care should be taken with large diameter ducts. Backfilling and tamping should be done without damage to the ducts. Temporary bracing can be used inside the ducts or angle rings can be permanently installed on the ducts to provide strength and rigidity. Rings should be primed and coated with PVC paint.
Polyvinyl Coated Ductwork Load Specifications
#1 Standard 4” – 8” 400 lbs./Linear Ft. 10” – 12” 600 lbs./Linear Ft.
#2 Corrugated 14” – 36” 1800 lbs./Linear Ft.
*All ducts 14” or more in diameter are corrugated for extra strength.
Where deeper burial or heavier loading is required duct gauges can be increased. Also angle rings and/or special bracing can be used.