Installing Foundations Close To Trees
Many houses share their plots with trees and plants that help boost the attractiveness (and subsequently the value) of a property. However, these same trees can also pose some very significant structural problems, particularly with foundations. The underlying problems are typically related to the tree's roots — if the root is compromised in any way, it will have some effect on the behavior of the underlying soil.
There are a number of problems that can arise from building foundations close to trees. The exact problem depends on the species of tree in question and the condition of the subsoil; however, some of the more common issues are given below.
Loss of Absorption
Most trees throughout Canada have lengthy radial roots which extend outwards in all direction under the topsoil. If any of these roots are damaged during foundation excavation, the soil will lose most of its absorption ability and can become water-logged. Water-logged foundations are notoriously difficult to construct and can pose major challenges for site developers.
Too Much Absorption
The converse also applies - too much absorption can result in shrinking foundations. During periods of sparse rainfall, the trees roots will absorb all of the moisture from the surrounding subsoil in an attempt to heal itself. If the saturated soil loses all of its water content, subsidence can occur, even in otherwise stable conditions.
This problem is exacerbated in new-build homes, as the foundations of these properties are typically shallower and more prone to displacing. Older houses, on the other hand, are able to withstand the onslaught due to their flexibility in construction.
The roots of each tree will behave differently depending on the tree's species and age. However, some trees have particularly invasive roots that can cause significant problems with foundation repairs. Conifers are one example of trees with invasive roots that can find their way into small cracks in the foundation. If the root is able to compromise the foundation, it may cause cracking in the concrete which can lead to eventual failure.
"Heave" is a geotechnical phenomenon associate with heavy, over-consolidated clays. If a tree situated on this type of soil is removed or weakened, water will ingress into the clay, causing it to rapidly expand. This rapid expansion causes the soil to bloat or "heave", placing enormous pressure on the foundation. This pressure can seriously damage the structural integrity of the foundation and is impossible to stop once the process has started.
The first approach of many developers is simply to remove the tree in the hope that clearing the area will relieve pressure on foundation. However, because of the complex relationship between the tree's roots and the subsoil, this is oftentimes not a good approach. If you suspect the presence of trees having an effect on your foundation, consider the following methods to solve the problem:
- Consider underpinning your foundation to increase its depth and thus its overall strength and stability. There are a number of methods commonly used to underpin foundations, each with their own benefits and drawbacks. For most problems relating to tree roots, a simple pile and beam solution will usually be enough to alleviate pressure on the structure.
- To stop problems related to invasive roots, consider installing a root barrier between the tree and your property that will stop the root from expanding near your home. Root barriers are typically structural "walls" that act as shields against root expansion. For other problems, barriers may not be sufficient as the root can still damage the surrounding soil.
- If you know your foundation is to be built on heavy clay, you will have to take protective measures prior to construction. One of the most effective ways to protect your home is by constructing foundations that limit pressure by taking the material deeper and lining the structure with a compressible material.