Below Ground Systems

Underground Range shot

Most domestic house drainage today is made from PVCu and is normally 110mm or 4inch in diameter and terracotta in colour. In some applicattions, a larger system 160mm or 6inch may be required, normally when 5 or more houses are connected together ans a larger capacity of pipework is therefore required.

All pipes and fittings supplied by SIG Drainage are manufactured to BS EN1401:1998 which means that with the exception of Chamber Risers, all pipes and fitting from different manufacturers conforming to this standard are compatible with each other.

Underground drainage is normally split in to two different systems:

  • Foul Water which handles waste water from bathrooms kitchens, utility rooms etc.
  • Storm Water which handles rainwater.


Foul Water

Foul water will normally enter the drainage system using a 110mm Soil Vent Pipe which should be suitably ventilated to prevent gas build up and syphonage.  A longer radius 87.5degree rest bend should always be used at the base of a soil and vent pipe stack; if it services at least one WC.

Kitchen or utility room sinks, dishwashers and washing machines can be connected to a soil stack or taken out through the wall in to a Roddable Bottle Gully. This has an internal trap system that prevents odours from the drain to escape and also has the facility to all you to rod pipework in the case of a blockage occurring.

The next point of connection is usually a chamber.  Chambers are used whenever there is a change in direction or size in the system in order to all access for testing, inspection or rodding to clear any blockage that might have occurred.  They are also fitted in straight runs over 45metres.  Man entry is not allowed and all rodding should be done at ground level.  Chambers come in two forms shallow access or inspection.

A shallow access chamber is used when the drain depth (invert) is 600mm or less.  Two versions are available, one with an inlet each side and one with two inlets to each side.  Although they are narrow chambers, because of the depth restriction, rodding is still very easy in both versions.  The finishing height can be adjusted by cutting the top riser section with a handsaw.

A lid / cover is then required and these are available as a pedestrian traffic only version which is 280mm, and a pedestrian and driveway version which is 315mm.

For depths greater than 600mm, the 450mm inspection chamber is used.  This can be taken down to 3m in depth using the relevant number of risers.  If the depth is more than 1.2m however, a restrictor ring is required to reduce the diameter to 350mm to prevent entry in to the chamber.  A 450mm chamber sealing ring is recommended.  As with the shallow access chamber the finished height can be adjusted by cutting the top riser section with a handsaw,

Storm Water

In most cases storm water is kept separate from Foul water, so rainwater run off is either taken in to a separate drainage system or in to a soakaway system.  The first connection point for the rainwater downpipe is either a universal drain adaptor which connects the two different sizes of pipework together or a roddable gully.  These then connect in to the storm water drain via branches or if required chambers.  Other means of collection of storm water are yard gullies or channel drainage.  As an alternative clearing access in storm water systems a rodding eye  can be used at the head of the drainage run or at intermittent points along a straight run.

A soakaway system is a temporary storage point situated generally in the garden of the property and is created by using a number of soakaway crates clipped together and surrounded by geotextile membrane.  This creates a temporary storage chamber that then allows the water to gradually soak away in to the ground.

All products marked in bold and referred to in the above sections are available through SIG Drainage.