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Simple plumbing for your bathroom

Simple plumbing for your bathroom

The whole idea when adding or moving bathroom fixtures is to take maximum advantage of your present plumbing. Replacing old fixtures with new ones in the same location is fairly simple. Installing new plumbing runs (called roughing-in) to place fixtures in new locations requires skill and planning. It also may require a plumbing license, so check with your local building department before doing such work. In any case, when planning to add bathroom fixtures, place them as close as possible to existing plumbing to keep new runs short. If you don't, costs can skyrocket.

Residential plumbing systems are easy to understand. In general, a home plumbing system consists of two networks of pipes. One is the supply system the pipes that carry water into the house and distribute it to all your plumbing fixtures. The other plumbing network is the drain, waste, and vent (DWV) system, which carries drain water, waste, and harmful gases out of the house. A complete diagram of typical supply and DWV systems is shown the opposite.


In the supply system, an underground line from a water source connects to a meter that measures the amount of water entering the house. Next to the meter is a shutoff valve that, when closed, stops water from flowing into the house. The main supply line branches into two lines-one for cold water and one for hot. The cold-water supply line feeds the network of supply pipes throughout the house. The hot-water supply line goes to your water heater. From there, the hot- water pipes run parallel with the cold-water pipes to serve various fixtures and faucets.

Your home's water supply system is pressurised, but the drain-waste system depends on gravity. These pipes also are connected to vents, which allow sewer gases to escape harmlessly up a chimney-likee vent stack. Plumbing vents also allow the entire DWV system to maintain atmospheric pressure so the flow of waste water is not affected by vacuums, back-pressure, or syphoning.

Drains and Vents

Because each new or moved bathroom fixture must connect with the main soil stack, you must know the locations of your main vents, then determine a route for attaching new vent lines to them. You may live in an area where building codes specify the size and general conformation of drainage, waste, and vent lines. So, once again, consult local codes and hire a licensed professional plumber, if necessary. Unless you're an accomplished do-it-yourselfer, it's best to leave major plumbing jobs to a professional.

Rerouting plumbing is much easier if the house has a basement or crawlspace. If the house is built on a concrete slab, adding new baths or fixtures may require demolishing part of the slab to gain access to main plumbing lines. Also, check to see if your water heater has enough capacity to meet the added hot-water demand. You may want to add another water heater.

Plumbing Design

When planning a bathroom, keep these basic rules and principles of plumbing in mind:

  •  Each bathroom fixture must have a drain with a trap a curved pipe that always retains a little water in it as a seal to prevent sewage gases from coming through the drain pipe and escaping into the house.
  •  Beyond the trap, each drain must be connected to a vent pipe that either goes directly up through the roof or connects to another vent stack. Plumbing vents (also called soil stacks) run from the lowest part of the system clear up to the roof. For cosmetic reasons, it's best to run vent stacks up through the back side of the roof, not the front.
  •  The drain-waste lines run to the lower parts of the house then exit to a city sewer system or a septic tank.