In the Field · Part 4
Materials and methods: PEX vs. copper vs. CPVC, ABS vs. PVC (it is regional), cast iron, and the transitions that fail
Every material a plumber runs is approved somewhere in the code's tables, and every one has a place where it fails: PEX at the water heater, copper at the galvanized nipple, ABS glued to PVC with the wrong cement, cast iron cut without a shielded coupling. This lesson is the working comparison a contractor needs to choose and to price: supply in PEX, copper, or CPVC; drainage in ABS, PVC, or cast iron; where the state code draws its lines (PEX not within 18 inches of the heater, dielectric transitions, listed transition fittings), where the regional convention decides (ABS in most of California's residential work, PVC in some jurisdictions and most commercial), and where a city's amendment overrides all of it.
What the full lesson covers
- Supply: PEX is the repipe default for cost and speed, run in a manifold or trunk-and-branch, with the code's limits (not within 18 inches of a water heater; PEX-AL-PEX not adopted for potable water in California); copper remains the standard for exposed work, heater connections, and jurisdictions or customers that want it; CPVC is lawful and less used.
- Every copper-to-steel joint is a dielectric transition: a copper alloy adapter, a 6-inch copper alloy nipple, or a listed dielectric union or fitting (CPC 605.16.1). Skip it and the galvanic joint fails in years.
- Drainage: ABS and PVC are both approved by Table 701.2; which one a region uses is convention and local amendment, and the two are joined only with a listed transition fitting or cement, never with ordinary ABS or PVC cement (605.16.2, 705).
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