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⌘ K
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DC Plumber: General Plumbing Knowledge, Materials, and Fixtures

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General Plumbing Knowledge, Materials, and Fixtures

Materials and their limits

  • Copper: Type K for buried service, Type L for general distribution, Type M for above-ground dry locations. Joints by lead-free solder, brazing, or listed press fittings.
  • PEX: cross-linked polyethylene, joined with listed insert or expansion fittings; must be protected from UV and physical damage and needs listed supports.
  • CPVC: hot and cold distribution, solvent-cemented; verify temperature and pressure ratings (commonly 100 psi at 180 F).
  • PVC and ABS: drainage, waste, vent, and some underground uses - never hot water distribution.
  • Cast iron: no-hub couplings or hub-and-spigot; used for soil stacks where sound and fire performance matter.
  • Materials contacting potable water must be listed to NSF/ANSI 61; plastic piping systems to NSF/ANSI 14. Lead-free means a weighted average of not more than 0.25 percent lead in wetted surfaces.

Supporting and joining

Support spacing follows the code table by material and size; as a working anchor, horizontal copper 1 in and smaller is supported at 6 ft intervals and vertical copper at 10 ft. Dissimilar metals need a dielectric union or insulating fitting. Plastic pipe needs allowance for expansion and must not be cemented with the wrong solvent - PVC cement on CPVC or ABS is a defect that shows up later as a joint failure.

Worked example

A crew is running a new 1 in water service under a public sidewalk to a rowhouse. Copper Type M is a poor choice here: it has the thinnest wall and is not intended for buried service where external corrosion and loading occur. Type K copper or an approved plastic service pipe is the defensible answer, with proper bedding, a tracer wire for plastic, and protection at the wall penetration.

Traps that cost marks

Mixing cement types on plastic; skipping dielectric isolation between copper and galvanized steel; using PVC cement on CPVC; supporting plastic at copper spacing; and assuming any brass labeled lead-free is acceptable without checking the listing for the application.