The Plumbing Rough-In

Plumbers work with three basic categories of supplies. There are the supply pipes that deliver the clean water into the house and to the plumbing fixtures, such as the sinks, toilets, and washing machine. It's the waste pipes that drain the water and other waste from the fix­tures.

THE SUPPLY PIPES.
Starting with the service line from the source—perhaps you have a municipal water supply, maybe a well on your property—the supply pipes extend into the home. The main cold-water pipe, called the trunk line, then divides, sending water both to the water heater and to the many branches that supply the fixtures in the house. The cold water supply is paralleled by a hot water trunk line and a second set of branches that provide the supply of hot water to the fixtures that require both. As with the blood vessels in the body or the branches on a tree, the pipes step down in size as the extremities of the system are reached.

Supply pipes can be iron, copper, or one of numerous varieties of plastic. Copper and plastic pipes are the rule today, but your plumber will look to the specifications to indi­cate what your job requires. In general, copper is more durable and expensive, plastic cheaper and easier to install. Whatever the material used, the pressure in the system is maintained at all times, so the pipes must be tightly joined. With copper, the joints are soldered, with plas­tic they're fastened with a solvent cement.

THE WASTE PIPES.
The waste system is not pressurized. It is dependent upon gravity to function, so all waste pipes must slope down­ward, away from the fixtures and toward the sewer or septic tank, dropping at a rate of at least Va inch per horizontal foot.

The waste system must also be vented, which means that the plumbing sys­tem will have a pipe that extends upward and vents outdoors, typically through the roof. That will allow the water and waste in the system to flow smoothly out to the sewer or septic tank. If there were no vent, the system would drain slowly or not at all, not unlike a water-filled straw when you seal one end with your finger. Vent pipes also allow septic gases to escape.

Every plumbing fixture must have its own trap, a U-shaped space built into the fixture (in the case of toilets) or in an adjacent pipe. The trap remains filled with water at all times, acting as a barrier to sewer gases that would otherwise rise up through the pipes and enter the living spaces of the house.