Above Ground Drainage
Above ground drainage covers everything from the appliance to the point a run drops below floor level: traps, waste pipe, the soil stack and the fittings between. Sizes run 32mm to 110mm in white, chrome and slate grey. Where the run continues below ground, see underground drainage.
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Choosing Above Ground Drainage
Frequently Asked Questions
110mm is the standard for a house stack taking a WC. 160mm is for a stack serving several flats or a commercial building where 110mm would be undersized. Waste-only runs from a basin, bath or sink use 32mm, 40mm or 50mm depending on the appliance, and join the stack through a boss.
32mm is for a hand basin. 40mm covers a sink, bath, shower, washing machine and dishwasher — anything discharging a larger volume. If in doubt, 40mm. Running a basin in 40mm is not a problem; running a bath in 32mm is, and it shows up as slow draining and gurgling.
A P trap where the waste runs horizontally into the wall, a bottle trap where it drops and space behind the basin is tight, and a shallow trap under a bath or shower tray where there is very little height. Telescopic versions take up the difference in a cupboard where the pipe centre does not line up.
Yes — without air entering the stack, a discharging WC can siphon the water seal out of nearby traps and let drain smells into the room. Traditionally the stack runs open to above roof level. An air admittance valve is the alternative where taking the stack through the roof is not practical, but at least one stack on the system should stay open.
Push fit seals on a ring, so a run can be dismantled and reused and there is no curing time — useful for a repair, or anywhere access stays open. Solvent weld is cemented rigid at every joint, which suits a stack that will be boxed in or a run sealed behind plasterboard, where a creeping seal is a real problem.