Polypipe 110mm x 92.5° Socket Double Branch, soil pipe fitting, drainage junction, double branch connector, SWU424 SG

Above ground drainage carries waste water from sinks, basins, baths, showers, toilets and appliances, and rainwater from the roof, down to the underground drains. It covers soil and vent pipe, waste pipe, traps, pan connectors, air admittance valves, and rainwater gutters, downpipes and their fittings.

Soil and vent

Soil pipe takes toilet waste and is most often 110mm outside diameter, with 82mm and 160mm sizes for particular jobs. Air admittance valves let air into the stack so trap seals are not pulled out, and can reduce the need for an open vent through the roof; those used under Building Regulations guidance should conform to BS EN 12380.

Waste pipe and traps

Waste pipe comes in 32mm, 40mm and 50mm nominal sizes. Solvent weld and push-fit systems have different outside diameters, so they are not interchangeable; join them with a universal or compression adaptor. As a guide, Approved Document H suggests a 32mm trap for basins and 40mm for baths, showers, sinks and washing machines, with a 75mm water seal for basins, sinks and washing machines and 50mm for baths, showers and toilets.

Rainwater

Gutters come in half round, square, ogee and deep high-capacity profiles, with round or square downpipes. Profiles and joints differ between manufacturers, so match the system and colour when extending or repairing.

Choosing the right parts

Measure the existing pipe's outside diameter, note the joint type and colour, and keep to one system. New work should comply with Building Regulations Part H. For pipework below ground, see below ground drainage.