Horizontal PVC drainage piping is being suspended below a floor structure. What is the maximum spacing between hangers for that piping under the IPC?
- A6 feet
Six feet is a spacing associated with smaller copper tubing, not with plastic drainage pipe. At six feet a warm PVC line will belly between hangers.
- B10 feet
Ten feet corresponds to larger copper tubing and to vertical support intervals for some materials. It is far too long for horizontal plastic drainage.
- 4 feet
- D12 feet
Twelve feet is in the range used for steel pipe, which is much stiffer. Applying a steel interval to plastic guarantees sag.
Why C is correct
Four feet is the maximum horizontal hanger spacing for PVC drainage piping. Plastic pipe is flexible and softens with warm discharge, so it needs closer support than metallic materials to hold its grade.
What this question is testing
Checks whether the candidate reads support intervals from the correct material row rather than applying one familiar figure to all piping, and understands why plastic needs closer spacing.
On the job
Sag is the enemy. A belly between hangers becomes a low spot that holds water and solids, and it shows up as a chronic slow drain that no cable will fix. On long warehouse runs, support at the required interval, use hangers wide enough not to bite into the pipe, and check grade with a level as you go rather than trusting the hangers to be equal. Warm discharge will find every weak point.
Memory technique
Plastic sags, so keep the hangers close.
Exam tip
Support spacing is a material question first and a size question second. Find the material row.
Where to look it up
IPC Chapter 3, general regulations, the hanger and support spacing table. The UPC publishes its own support table with some different intervals, so confirm in the code your state adopted.