Tree roots – is your house cracking up?

January 16, 2015

Do you have an unsightly crack in one of the walls of your house?  You’ve patched and painted it several times and yet it keeps returning? Depending on where you live, there’s a chance that the cracking is simply due to your house being founded on reactive clay. However, another possible cause – one that is often overlooked or dismissed – is growing and expanding tree roots. Different trees have different root systems which exhibit different behaviour and characteristics. And, whilst we’re certainly not claiming to be arborists, we know enough about tree roots to know that they can cause some serious damage to houses.

Tree roots seek out moisture in the ground. When we’re involved in investigations and excavations to expose offending tree roots, it’s not uncommon for us to uncover cracked or leaking plumbing pipes contributing to the problem.   Lots of Sydney houses still have the old terracotta, segmented pipe systems for their in-ground sewer and stormwater plumbing.  Movement in the ground can lead to cracking or failure of these old pipes, resulting in water & moisture discharging into the surrounding soils.  In the case of sewer pipes, the water can be nutrient-rich, and tree roots seek this out – eventually invading the pipe system and exacerbating the situation.  So, if you’ve got cracks appearing in the walls that are near or part of your wet areas (e.g. toilets and bathrooms), chances are that leaking, faulty, or broken plumbing pipes are part of the problem. (Of course, this isn’t necessarily exclusively a tree problem – leaking pipes can cause consolidation or flushing away of the foundation soils if your house is founded on sand or loam, or it can cause swelling of the underlying ground if your house is founded on clay). But back to the tree roots themselves…roots can pass under or penetrate through the footings of your house. As the tree grows, so does the size and diameter of its roots.  Once a root come into contact with the underside of the footing, it then pushes against and exerts an upwards force.  And, whilst you might think that your two-storey, brick walled house is too heavy to be pushed up by a humble little root, you’d be amazed at how easy it is for a root to cause cracks to open up in masonry walls.  We’ve included a few photographs of what we’ve uncovered in recent times!

The other trick is to not discount or dismiss trees that you think are too far away to be the source.  We encountered a house in Kensington (Sydney) where a thick root – about 150mm in diameter – was pushing up the front verandah of a house.  With a bit of digging and further investigation, the tree that belonged to the root was actually more than 15 metres away!

So, having established that a tree root is causing the problem, what should you do next?   Here are our recommendations:

  1. Get a structural engineer to inspect the cracking.  Your engineer should establish whether the cracking is merely cosmetic at this stage, or whether the crack has advanced to being “structural” and thus requires a more involved repair procedure.
  2. Contact an arborist and get advice as to the likely future behaviour of the tree.  Will it continue to grow and cause further damage, or is it fully matured and unlikely to present further threat?
  3. Is it an option to simply sever and cut back the root?  Your arborist can advise whether this is feasible, or whether it’s likely to harm or de-stabilise the tree.  The arborist should also be able to advise whether severing the root will put an end to the problem, or whether the root will simply start to re-grow and return to cause damage down the track.
  4. Sometimes, depending on the situation, you may need to consider having the tree removed.  This is a delicate issue, and different Councils have different policies as to what you’re permitted to do.  The situation is particularly tricky if the tree in question is on your neighbour’s property!  At the very least, contact Council and seek their advice and permission before organising anything too drastic.  Sometimes, Council may require a report from both an arborist and a structural engineer to establish that removal of the tree is warranted and the only option available to prevent damage to your house.

Needless to say, Partridge gets involved with inspecting houses and preparing reports on cracking all the time, (one or two reports every week, in fact!) and we’ve got plenty of experience in dealing with trees and recommending appropriate repairs to suit the situation. Drop us a line if you need our advice.

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