Why Do Tree Roots Cause Subsidence?

Subsidence is every homeowner’s worst nightmare. It’s something that property owners alike, whether commercial or domestic, will do their best to avoid, but what if the cause of subsidence issues is, to a point, beyond your control? There are many different causes of subsidence, but it’s often caused by a combination of different factors, rather than one thing alone. However, we’re going to be focusing on two contributing factors in this article: clay soil shrinkage and trees. How, exactly, do these two contributing factors cause subsidence when combined with each other? Let’s take a look in more detail:

What is subsidence?

Subsidence refers to the sinking of a property, whether it be commercial or domestic. It happens when the building foundations have become compromised, which can happen for a variety of different reasons. Subsidence can cause severe damage if left untreated, but the signs of subsidence are evident, especially for homeowners. Some signs of subsidence include, but is not limited to, the following:

• Cracks in walls, floors and ceilings that are more than 3mm wide
• Cracks that run in a zig-zag line or that run along the mortar lines
• Cracks around doors and windows
• Doors and windows becoming jammed
• Doors and windows that cannot be closed
• Puddles that form on once-flat patios, driveways and garden paths
• The property is noticeably leaning to one side
• Creases in wallpaper where there aren’t any damp issues present
• Your extension coming away from the rest of the house

How do tree roots cause subsidence?

Not all trees will cause subsidence issues, but it can be a problem with shrinkable clay soils. It will also depend on how deep or shallow your foundations are. Typically, properties that were built before the 1950’s and are more than two storeys high are most susceptible to subsidence, especially if a tree is planted close by. However, tree roots combined with clay soil and older properties is the perfect recipe for subsidence problems. So what issues to tree roots really pose? 

Firstly, tree roots will grow a considerable length to seek out moisture. If it can’t find any water in the location it has been planted, then it will seek out water a significant distance away in order to survive. Sometimes, this can cause tree roots to run underneath your property, especially if it sits on shallow foundations. In turn, the tree roots will suck out any moisture it finds, causing the soil to shrink in the process. As a result of soil shrinkage, it can cause a shift in the foundations, which is also referred to as subsidence.

Another issue with tree roots is that, depending on its size and species, they have the potential to crack drains that sit under the ground. Where this might not affect your house directly, it will eventually cause problems further down the line. If a tree root has cracked a drain under the ground, it causes a considerable amount of water to leak out into the surrounding soil, thus softening it. This newfound soil softness allows for movement, and that includes the movement of your house foundations, otherwise known as subsidence.

Which trees are more likely to cause subsidence?

Despite tree roots being a common culprit for the occurrence of subsidence on both domestic and commercial properties, some trees are more prone to causing such structural issues than other species. For example, trees that require less water to survive are less likely to cause subsidence issues, whereas those that need a copious and ongoing supply of moisture will mean that, sooner or later, you’ll need to enlist the help of an underpinning professional, such as us here at Geobear, to rectify your subsidence issue. So which trees should you be wary of near your property?

Trees that are most likely to cause subsidence are aptly named ‘high water trees’. Essentially, it refers to any tree species that needs a lot of water from the ground in order to live. Where you should refrain from planting these types of trees near your house anyway, regardless of soil type, you should be especially reluctant if your house sits on clay soil. High water trees include:

• Aspen
• English Oak
• Goat Willow
• English Elm
• White Poplar

If you find these around your property, more so if you know your house sits on clay soil, then you should make provisions to have these removed as soon as possible, or relocated to an area that is further away from your property. However, it is possible to have them chopped down, but you will need to make sure that you check that they do not have a tree preservation order (TPO) on them, because it could land you with a hefty fine. If you’re looking to have trees in and around your land, but you’re concerned about subsidence, then plant them as far away from the house as possible. You should also choose low water trees because they don’t require lots of water in order to survive. Low water trees include:

• Hazel
• Elder
• Silver Birch
• Holly
• Hornbeam

Other causes of subsidence

We’ve already discussed, in detail, how tree roots can cause subsidence, but what other risk factors are there that can cause the same issue on both commercial and domestic properties? From the local and surrounding environment to the property itself, here are a few other causes of subsidence, aside from trees and their roots:

• Clay soil shrinking and expanding with the changing weather and seasons
• Water leaks from drain pipes and gutters
• Soil or bedrock becoming eroded
• The property is built on an old mine or a filled-in quarry
• The age of the property itself
• A lack of foundation integrity as it ages 

Geobear is pleased to offer subsidence solutions to both commercial and domestic clients alike. Regardless of the severity of your issue, we will have a subsidence solution that will meet your needs and stand the test of time, including a specialist tree root subsidence treatment. If you would like further information about our innovative underpinning technology, then get in touch with a member of our friendly, professional team today – we’re always pleased to hear from you.