How to get it right: Above ground drainage

One of our surveyors came across this on site recently:

At first glance it looked like someone was trying to compress a 100mm toilet discharge pipe into a 32mm waste pipe. On closer inspection our surveyor discovered that the toilet had been repositioned internally after the connection had been made through the wall. 

Rather than drilling twice the resourceful householder just fed the bath waste through the toilet bend.

Further issues with these drainage pipes

Aside from the different coloured boss connections to the pipe waste, there were a few more things not quite right with the drainage arrangement. 

As this is a wash basin waste, the minimum waste pipe size needs to be 32mm diameter. However the maximum branch length for 32mm diameter connections is 1.7m so the pipe size needed to be increased to at least 38mm for the 2.4m span. 

There were also a few support brackets needed. These should be in line with the manufacturer's recommendations but are usually around 1m centres. 

Without support brackets the pipework will sag over time, risking blockage and separation of the compression couplings. 

Most importantly, the 100mm waste needed removal so that a neat finish to the wall could be created and prevent cold bridging around the pipe. In the moist environment of a bathroom, if this was not done, it would have led to unsightly mould growth in a short space of time where the pipe passed through the wall.

Just on the left out of view, the waste passed over the bath waste before connecting into the front of the soil stack. This also needed adjustment; the bath waste pipe above needed increasing to 38mm diameter and was repositioned to connect higher into the soil stack boss allowing the wash basin discharge pipe to be clipped to the wall underneath and connect into the side of the soil stack instead.

Further reading

Visit the Polypipe page for details of drainage courses, registered details and drainage-related blog posts.

Read How to get your drainage right or view our current drainage training courses.