Above ground plastic DWV applications introduce a different set of issues that can add cost and complexity to high rise commercial construction projects. For example, a lack of understanding of hanger requirements can lead to improper installations.
Plastic must be supported by metal hangers every four feet in horizontal installations. Cast iron, on the other hand, needs only to be supported every 10 feet and within 18 inches of the joint.
The cost of hangers, anchors, connectors and extra labor in a typical plastic installation can be up to 2.5 times that of cast iron in horizontal applications.
And unlike cast iron, plastic expands and contracts with changes in temperature. The rate of thermal expansion for plastic is approximately .36 inches (PVC) and .66 inches (ABS) per 100 feet of pipe for every 10 degrees Fahrenheit. Installing plastic in high-rise construction requires the use of expansion joints to compensate for expansion and contraction.
For vertical stacks in multistory applications, compensation for expansion, contraction or building settling is often accommodated using offsets or expansion joints. Expansion joints are also necessary on horizontal runs exceeding 20 feet – once again adding cost and complexity to the system. And expansion joints can create problems during water testing of the system because they can leak if not properly installed.
Expansion joints are required in vertical stacks at every other branch interval and on horizontal runs exceeding 20 feet – once again adding cost and complexity to the system. And expansion joints can create problems during water testing of the system because they can leak if not properly installed.