Header height for commercial fixture banks
When working with PEX, the main header for the piping is actually kept higher than you typically would with copper pipe. For the branches that come off that header to go to each individual fixture, a higher header allows the installer to use the flexibility of the pipe and reduce the number of fittings. Just bend the pipe to the fixture connection rather than putting in an elbow.
Sometimes you need an elbow
When the use of an elbow is necessary -- say, to avoid vent piping -- the elbow can easily be put in place, and the remainder of the piping can then be run over to our fixture termination as necessary.
Expansion and contraction
When you introduce hot or cold water to plastic pipes, they expand and contract much more than metallic systems do. While not usually an issue with pipes less than 1", larger sizes, restrained in pipe clamps, will need to factor the size change in.
Uponor makes a PEXa pipe support product that is a half-round, 23-gauge galvanized steel channel. It snaps on to the bottom of the pipe and can reduce expansion and contraction by up to 93%. It also allows for increased hanger spacing; with the PEXa pipe support product, ½” and ¾’ size pipes can have 6' hanger spacing, and 1” and larger pipes can have 8’ spacing.
For bare PEX spacing for horizontal applications, most IPC jurisdictions are going to require 32” on-center for all pipe sizes; for UPC jurisdictions it’s going to be 32” on-center for up to 1¼” pipe; larger pipe can be spaced at 48” on-center. Both codes require support every 5' vertically.
Plumbing codes still require the use of water-hammer arrestors with PEX tubing. Even though the pipe is more flexible when the water hammer occurs it will transfer back through the piping system to the building components. Water-hammer arrestors will help the system operate more efficiently and last longer.