Foundation and Cracking Problems

The main reasons for foundation movement or failure would have to do with the soil conditions and surrounding factors.

Large trees in the area and poor drainage contribute to most problems to foundations.

You can not rule out though that human error could be to blame due to incorrect foundation depth, steel reinforcing positioning or lack of, incorrect foundation design and strength, or just generally taking short cuts during construction.

Large trees have been known to affect external walls of dwellings up to twice there height, so if the tree is 30m high then there roots could travel up to 60m away under ground.

Tree roots basically provide two functions, giving the tree stability so it's able to stay upright and provide the tree with a food source, one being water.  As the tree grows bigger and higher, the root system has to grow as well, travelling further away in search of food.  If there are or have been drainage issues to the property, then the roots will hone in to this area as a good food source. If and when the drainage problem is rectified, the tree roots remain taking all the moisture out of the soil causing the clay to shrink. The higher clay content the more shrinking will occur.

The moisture content of ground in and around the dwelling should remain the same from winter to summer, this ensures a stable foundation.

If large trees are present around the property and you would like to protect the structure from the root system, a root barrier system can be installed under the ground between the dwelling and tree about 1.5 meters from the dwelling.  A root barrier is a 100-200mm trench about 2-3 meters deep full of concrete with a membrane at one side.  The trench should be long enough so the tree roots can not go around the trench near dwelling.

If movement is apparent to a section of the dwelling and is increasing in size, then it is advised to have the area inspected.  A Buy-Wise inspector can compile a report on all the contributing factors in regards to the movement, and advise on the best course of action.

The next course of action may be obtaining a soil test (Geotechnical Report) and an Engineers Report to determine if the best solution is underpinning the existing foundations. On average, the soil test and engineers report could cost between $1500-$3000 depending on the circumstance.

The cost to underpin foundations can be between $5,000-$40,000 + so it is important to gather all the correct information to determine if this course of action is required, or other cheaper methods could be adopted with the same result.