Part 44: MEP Installation starts with the Plumbing
November 15, 2016
The supply lines that enter the house are installed to serve the mechanical, electrical, and plumbing (MEP) fixtures shown on the construction drawings.
This includes power and communications cables, gas line, special fluids, and a main water line with hot and cold branch lines to the sinks, water closets, baths, and outside faucets. The work begins with the plumbing rough-in.
PEX supply lines
Soldered copper tubing has been largely replaced by polyvinyl chloride (PVC) and chlorinated polyvinyl chloride (CPVC) tubes and fittings. Both of these synthetic plastic polymers are said to have latent environmental problems (see this article at Healthy Building Science).
Based on toxicity studies for water supply lines, flexible cross-linked polyethylene (PEX) tubing has shown to be a sustainable alternative to PVC installations. PEX tubing has gained in popularity because its simple installation makes it far less expensive, easier to maintain, and not as prone to environmental contamination.
The PEX system shown in this example includes hot and cold water supplies in combination with recyclable high density polyethylene (HDPE) waste and vent pipes.
In cold climates, the main water supply runs below the local frost line, up into the building through a slab or insulated floor frame, into an insulated mechanical closet that houses a PEX distribution manifold.
One branch of the water line flows from the manifold to a water heater and then back to the hot side of the manifold. Branch tubing then runs from the hot and cold sides of the manifold to shunt valves for each plumbing fixture.
The PEX tubing is color coded red and blue for hot and cold and is strung through the framing like wiring as a single continuous line. There are no inline joints or spliced connections to fail (see www.pexsupply.com).
Be cautious of gas lines
With an abundance of caution, black iron gas lines are installed from the gas meter to the in-line hot water heater, dryer, and kitchen fixtures in lieu of the less expensive corrugated stainless steel tubing (CSST) normally found in most residential construction.
Building codes govern gas pipe material, size, and wall thickness for all underground service. Note that local codes also dictate the size and location of holes cut into the framing as well as the use of protective plates to prevent accidental punctures.
(To be continued…)
The material presented in this series has been taken from our book, “How a House is Built: With 3D Construction Models” The book includes annotated illustrations, captioned text, videos, models, and the 2D Preliminaries.