How does the tree in your garden or the pretty oaks lining your pavement affects your house foundations? Find out about the connection between trees and foundation damage.
There are many factors that could cause damage to house foundations and result in subsidence – the downward movement of a property as a result of subsoil damage.
Some causes are natural factors such as the type of soil the house sits on or rainfall/weather conditions and some are man-made problems including insufficient drainage or blocked systems.
However, one of the most common reasons for subsidence damage is, in fact, tree roots! Whilst it may be appealing to have a leafy garden filled with trees or the pavements of your street lined with them, if trees are too close to the buildings, they can actually affect the structure of the foundations and cause substantial damage.
Don’t be too scared by this article – modern houses are rarely affected by this kind of damage and tree root damage is mostly restricted to older houses (pre-1970’s) and those with insufficient foundation depths.
Find out more about subsidence damage and how to fix it in our blog
How do trees cause foundation damage?
As subsidence is caused by changes in soil conditions, tree-related damage mostly impacts foundations built on ground surfaces with high proportions of clay material. Tee roots absorbing minerals and moisture from the ground, causing the groud to shrink. As trees grow and the root systems become more expansive, they absorb more moisture from a larger area and the soil shrinks further, this causes movement of the ground. This ground movement can lead to subsidence and eventually, damage to building foundations.
In times of drought, this problem is increased and more soil shrinkage takes place in high Summer. This is known as ‘seasonal deficit’ and occurs when soil becomes drier in Summer and rewets in Winter.
Trees and Foundation Damage: Where can I plant trees and which trees should I avoid planting?
The amount of moisture a tree absorbs is usually determined by the species of tree, its mature size and the damage caused is related to its proximity to the building. Generally, the larger the tree, the larger and more expansive the root systems – meaning they absorb more moisture and minerals. It is estimated that tree root systems can be between 1-3 times the size of the tree itself. The closer the tree is to the building, the more impact it will have on the soil conditions.
This doesn’t mean you can’t plant any trees near your home, as with careful selection and distance you can still enjoy a leafy garden or a green pavement. Select trees that are slow-growing, with less aggressive rooting patterns to limit potential of subsidence damage.
ABI identify the most potentially damaging trees to avoid planting are Oak, Willow, Sycamore, Ash, Plane and Poplar and have compiled a handy list of tree types and recommended distances from building.
How can I prevent trees from damaging my house foundations?
There are several ways to prevent root damage to your foundations:
Firstly, research and follow advice on which trees to/to not plant and how far they should be from the building.
Another option to prevent tree foundation damage is to build a root barrier. Mechanical root barriers are made from corrosive resistant material and essentially form an extra wall around your house foundations that prevent roots from reaching the concrete and the soil around it by redirecting them downward.
Chemical root barriers work by forming a chemical protector around the foundations and killing the roots before they come in contact with the foundations and surrounding soil.
What if there is already a tree near my house? Should I remove it to stop it damaging my foundations?
If you have a tree near your home and are worried about it causing foundation damage – don’t hurridly chop it down just yet! Sometimes, removing a tree can also cause damage. Removing the tree roots can adversely affect the soil conditions by causing too much moisture in the soil – causing it to swell and resulting in ‘heave’ of the foundations. It is best to consult a tree surgeon before removing a tree.
It is also worth noting that some trees are protected by Tree Preservation Orders and are not allowed to be removed. Make sure to check this before having it felled.