Tree roots are the most common cause of in Australia. Condensation that forms on the outside of sewer and stormwater pipes attracts tree roots, especially in the hot months of summer when less water is available for thirsty tree roots. Over time the tree roots will tend to burst through into sewer and stormwater pipes, and as the roots infiltrate the pipes they will catch debris and cause a blocked drain.

Tree roots are often worse for drain pipes than a simple blockage. Even when the roots causing the blocked drain have been cleared by a plumber, the pipes will remain damaged where the tree roots broke through. The water that leaks out will attract further tree roots which may then enter the drain, eventually causing it to block again. When a pipe is penetrated by tree roots it also often creates a ‘lip’ that serves to catch material flushed down the drain, making it easier for the drain to become blocked. The only permanent solution for drains that continually become blocked by roots is a drain camera inspection to identify the problem section of pipe, and then to excavate and replace it.

There are some steps that can be taken to reduce the risk of a blocked drains caused by tree roots. For all new and replacement drain installations, PVC pipe is recommended as the best below ground pipe material to stop tree roots. If installed correctly there is a much reduced chance of root penetration. PVC pipes are also unlikely to collapse with ground subsidence, and typically come with a manufacturer’s guarantee for 50 years.

When it comes to tree roots, it can be difficult to prevent problems from the roots of pre-existing trees. Having said this, after clearing a blocked drain your plumber should be able to identify how far down the line the blockage occurred, and where the blockage was caused by tree roots, which tree or trees are likely to be the cause.

New trees should not be planted in the vicinity of your drain lines. If you are unsure exactly where your drains run, ask your plumber. Before planting new trees it is also worth doing some research into which tree species will best for your garden and your drains. That small plant can very quickly becomes a big tree with an extensive root system that may cause blocked drains. Later removal can be costly, and in a lot of cases may be restricted by your local council. Information should be available on the size that most common trees typically grow to as well as the likely size of the root structure.

Sydney Water publishes a useful Fact Sheet titled which provides a list of problem tree species with a damage rating, and many local council websites will also list known problem tree species.