The Washington Suburban Sanitary Commission (WSSC), which rules the work of the plumbers in my neck of the woods, would never pass any new water plumbing in an exterior wall under any circumstances.
The WSSC is a very conservative agency. They will not even allow plastic water service laterals. They were early adopters of the first plastic piping and as the old hands will remember that was a mistake they do not wish to repeat. All of the plastic laterals that they allowed failed in a very short time.
They now except Pex and CPVC in interior piping but they will have nothing to do with plastic underground because of it's early history. They are quite clear that no form of plastic will be allowed for any pressurized piping until that type of plastic has many years of successful use elsewhere with water utilities which have the same water chemistry that they have.
The plastics industry brought suit but to no avail. The documented history of the previous failures with plastics produced by those same manufacturers, who swore at the time that it was the greatest thing since sliced bread, has been very convincing to the courts.
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Tom Horne
