Under-slab sewer drain basics
Above is an under-slab domestic house drain recently installed by Sonic Plumbing in Brisbane.
When installing an under slab sewer drain for your new house or renovation there are some important considerations and steps to follow. Here i’ll outline the basics;
Ensuring waste points are marked out accurately Having a detailed and accurate plan to work off is extremely important. You can save a lot of time and effort by spending extra initial time on the waste point mark-out. always measure twice, double and triple-check points that will be penetrating into walls.
Excavating and laying drain to the correct grade Over-excavating can be costly in time and bedding materials, so make sure depth is monitored during the excavation. Australian standards dictate 100mm sewer drains (as in the video) must be laid to a minimum grade of 1.65% (or 165mm per 10m of drain) The angles of bends waste pipe lengths should be marked out prior to excavation to minimise the usage of multiple bends for a single direction change.
Ensuring all PVC pipework joints are properly primed before glueing Aside from making sure your cuts are square, burrs removed and edges chamfered, priming fluid is a key consideration for joining PVC drains. Priming fluid for drains installed in Australia must be dyed red so properly primed joints can be clearly identified. unprimed joints are likely to leak inviting root intrusions into your drain system.
Concrete support under inspection points, traps and gullies Traps, gullies, Inspection risers and stack-points must be supported with a concrete base. Giving these points extra strength is necessary as they are the most likely outlets that will be serviced by drain cleaners and machines.
Water or air testing drain after completed Before inspection and backfilling the completed drain your local authority may require you to test the drain either by filling with water or pressurising the system with air.
Wrap risers where waste point penetrates concrete. Before the concrete pour you must clad the waste penetrations with 10mm foam to allow for expansion. a cracked waste pipe may cause long term drain issues. some authorities may require penetrations to be double wrapped depending on slab thickness.
If you’re in Brisbane and have an under-slab drain to install either for a new home or renovation, don’t hesitate to email your plans and any useful information to info@sonicplumbing.com.au for a free quote!
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