Choosing the right material and size of water supply piping is critical to a successful plumbing job. Here’s a closer look at the choices:
Plumbing Supply Pipe MaterialsPlastic pipe is used in many plumbing applications because it’s relatively inexpensive, easy to install, and impervious to corrosion. However, in some locations, plastic pipe is not allowed by code for water supply piping, so check with your building department.
Rigid pipe may be PVC (polyvinyl chloride) for cold water or drain-waste-vent (DWV) plumbing, CPVC (chlorinated polyvinyl chloride) for hot and cold water, and ABS (acrylonitrile-butadiene-styrene) for DWV piping. Flexible plastic tubing is made from PB (polybutylene) and PE (polyethylene). All plastic piping is rated for the pressure it can handle; this rating is stamped on the outside of the pipe.
Rigid copper pipe is widely preferred for water supply piping. It’s sturdy and durable, resists mineral buildup, and can handle both cold and hot water. Hard supply pipe is sold in three thicknesses: M (thin wall), L (medium wall), and K (thick wall). Most above-ground plumbing is Type M.
Soft copper pipe is more expensive than hard copper pipe, but it is flexible enough that it can be routed without the need for as many fittings as rigid copper. Type L is more commonly used than Type M for above-ground applications.
Both kinds of copper pipe can be joined with permanently soldered fittings or flare/ compression fittings that can be disassembled.
Galvanized iron pipe and fittings were standard for water supply plumbing before 1960 and are still common. The galvanized zinc coating on the outside resists rust and corrosion, but over time the insides of the pipes clog up with mineral deposits and eventually corrode. Watertight connections are made with threaded fittings. Larger-diameter galvanized iron pipe is used for vent plumbing in some houses.
To prevent corrosion from the electrolysis that occurs when two dissimilar metals are joined together, a dielectric union should be used anywhere copper is connected to an iron pipe.
Cast iron pipe is a strong, durable material used for DWV plumbing. Two types are common: the older “hub” or “bell-and-spigot” type joined together with lead and oakum, and the newer “no-hub” or “hubless” fittings connected with special rubber gaskets and stainless-steel band clamps.
Plumbing Supply Pipe Sizes
When adding new plumbing fixtures or appliances to your home, the first thing you’ll need to consider is whether your water pressure is good enough to support your additions. Check local building codes to find out the “fixture units” (a rating that represents the cubic feet of water used per minute) of an appliance or new fixture. This will tell you what type and size of pipe is recommended at the hookup.
If you are planning a major remodel or addition, to find out what size pipe to use, calculate the fixture unit ratings for all your fixtures and appliances and then approximate the length of the distribution pipes. In most cases, the main pipeline from the street to your home is either 3/4 or 1 inch in diameter, supply branches use 3/4-inch-diameter pipe, and pipes for individual components are 1/2 inch.
Remember that water pressure decreases by a half-pound per square inch for every foot pipes extend above your water supply. For ideal water pressure to second- and third-story fixtures, you might need a larger pipe. Your local building code can help you determine the right size pipe in these situations.
