In old installations, pipes for both supply and waste may be lead or iron. In modern homes, the supply piping is most likely to be copper, with soldered or compression joints, and the waste plumbing plastic, with push-fit or solvent-cemented joints.
Copper pipe for domestic plumbing comes in two main sizes: 15mm and 22mm. These sizes are measured over the outside diameter of the pipe, and replace pipes of 1/2 and 3/4in, which were measured over the inside diameter. The size used depends on the rate of flow through the pipe and the amount of pressure loss which can be accepted. 15mm pipe is used for individual connections to sink and basin taps, 22mm pipe for the outlets from the cold water cistern and hot water cylinder and for connections to bath taps. 28mm pipe (which replaces 1in) may also be used where high rates of flow are required: for central heating boilers, for example.
Fittings for copper pipe come in both compression and solder types. A wide variety is available, including tees (for connecting three pipes together), bends, tank and tap connectors, valves and adaptors for connecting pipe of different sizes (including adaptors to connect new metric pipe with old Imperial-size pipes).
Plastic supply piping
Plastic piping is available in the same sizes as copper pipe, and for both hot and cold water supplies. Plastic piping is much less susceptible to frost than copper.
CPVC plastic piping is relatively rigid, and is usually joined using solvent-welded fittings – the plastic equivalent of a soldered joint on copper pipe.
Polybutylene pipe is more flexible, and is usually joined using ‘Acorn’ push-fit connectors which include a rubber o-ring seal and a grab ring to hold the joint in place. These fittings can also be used with copper pipe.
The traditional materials for waste pipes were lead for the branch pipes leading from each sink, basin or bath, and cast iron for the hopper head and vertical waste pipe on the exterior wall.
Modern waste piping for sinks, basins and baths is abs or upvc plastic, and comes in three sizes: 32mm (l 1/4in), 40mm (1 1/2in) and 50mm (2in). It is usually white.
Connections may be solvent-cemented, push-fit or compression types, and a wide range of fittings is available including traps of various types, elbows and tees. The compresson joints have rubber sealing rings and should be tightened by hand – not with a spanner or wrench. Larger pipes – for the waste from wcs and for the soil stack – should be upvc, with push-fit or solvent-cemented joints.
All sinks, basins, baths and showers ЎЄ and appliances like washing machines and dishwashers which have been plumbed in – must be fitted with a trap to seal off the waste pipe (wc pans already incorporate one).
The traditional sink or basin trap is a simple u-bend formed from lead pipe, with an access plug at the bottom. The modern equivalent is the plastic p-trap, but this is only one of many types now available. Note that the outlet points slightly downwards to prevent water running back into the trap.
s-traps are similar to p-traps, but have the outlet pointing vertically downwards. Bottle traps are compact, but get blocked more easily than p- and s-traps. Shallow traps may be used where space is limited -under baths, for example – but should be used only with a two-pipe waste system. With single-stack systems, only deep traps should be used.
Traps with connectors are available for plumbing in washing machines and similar appliances.
An overflow must be provided wherever there is a ballvalve ЎЄ in cold water cisterns and WCS. In older homes, overflows may be copper or lead. Modern overflows are usually 22mm pvc with push-fit connections.