How do tree roots cause subsidence?

During dry spells of weather, the thin fibrous “finder roots” from trees stretch outward in search of water. These roots only last around a day while some finder roots might last longer, depending on the species. Despite their short lifespan, they’re continuously replaced, expanding and absorbing water. Over time, the roots desiccate the soil, causing it to sink or shift which increases the risk of subsidence.

What are the risks of tree subsidence?

Large, mature trees may increase the risk of subsidence, particularly in areas with clay soil. However, it doesn’t mean that if you have a large tree in your garden, it’s an automatic risk. There are a couple of factors to bear in mind, such as:

• Shallow foundations: these are typically found in single-storey extensions and are particularly susceptible if they’re located within a tree’s zone of influence (the area where roots can reach). Victorian properties, bay windows, and porches can also feature shallow foundations.

• Buildings have their own zone of influence, typically to a depth of 2.2 metres around the foundations. If roots disturb this area, they can destabilise the ground which can lead to subsidence.

• High plasticity clay soils: this type of clay undergoes significant volume changes, expanding and contracting with changes in moisture. That makes it especially sensitive to root desiccation.

Understanding these conditions can help you identify if your home is at risk of tree subsidence.

Luckily, new building guidance introduced in January 2025 recommends deeper foundations where trees are nearby, typically extending at least 0.5 metres beyond the depth influenced by tree roots. This helps reduce the future risk of subsidence in newer homes. But if you already have a large tree that’s affecting your foundations, what are your options?

How to Fix Subsidence Caused by Trees

If you’re dealing with existing subsidence, or want to prevent the risk, the quickest solution that may spring to mind is to remove the tree completely. However, this is not the preferred remedy. Removing a tree can change the moisture content in the ground, potentially causing heave or subsidence as the soil recovers. Tree roots also bind soil together, so their removal or decay after tree removal can result in micro voids.

We need to ensure there is a balance between protecting your home and preserving the trees. Remember, insurers want a permanent fix so, you’ll need to find a solution that addresses the subsidence damage and its underlying cause.

We use a combined methodology approach at Mainmark. As well as treating the subsidence damage, we can reduce the risk of roots getting near the foundations in a way that protects both the property and the tree. Our combined methodology involves two elements:

• Ground improvement works: this is to stabilise and re-level affected foundations. Teretek® is our reliable re-levelling solution that’s fast and non-invasive

• Installation of a copper geotextile root barrier: which is a non-invasive system that prevents the roots from reaching your building’s zone of influence. The copper is embedded in a geotextile membrane that forms the barrier. Copper (Cu²⁺) ions are naturally unappealing to roots, so, they encourage them to divert away from your home without harming the tree.

It’s a forward-thinking way to fix subsidence and reduce the risk of recurrence.

Working together with nature

Nature is nature and will always do what it needs to survive. So, instead of fighting it, we need to do our best to work alongside it, which is what makes our approach different.

Tree Preservation Orders (TPO) mean it’s becoming increasingly difficult to remove entire trees as they protect the whole tree and root network. Rather than working against this, it’s best to adapt and mitigate.

Our combined methodology provides a solution that protects homes while preserving the trees. It’s quick, non-invasive and backed by long-term warranties: up to 50 years for our Teretek® re-levelling solution, and 10 years for the copper root barrier system. Together, they offer peace of mind for years to come.

Are you worried about tree subsidence and want to know more? Get in touch and discover a smarter solution.