Foundation Issues

The Risk of Tree Roots Causing Subsidence

A tree’s influence starts, literally, at the roots; they are responsible for keeping the tree alive by drawing essential nutrients and water from its surroundings. The roots will continue to grow as a tree matures and during this growth, the roots will extend towards anything that will maintain the tree’s life.

Tree roots typically seek out moist soil and can infiltrate old or damaged pipes, including sewer and water lines. When a tree is removed, its roots no longer absorb water, which can lead to soil displacement and potentially harm the building’s foundation.

Seasonal changes also affect how trees interact with the built environment. During the warmer months of spring and summer, soils can dry out, causing reactive clays to shrink. In extreme cases, this shrinkage can result in significant ground movement, subsidence, and foundation settlement. Unfortunately, trees can worsen this situation. As they search for moisture, tree roots extend into the dried soil, further depleting the moisture and exacerbating the dryness.

The risk of tree roots causing subsidence arises from the combination of dry soil and thirsty tree roots, creating an ideal environment for ground movement and concerning symptoms of subsidence, such as cracks in brick walls, distorted timber frames, and jammed doors and windows. For examples of various causes of subsidence around the home, including those related to tree roots. Understanding the root causes of these issues is crucial for identifying viable solutions.

Assessing the Influence of Trees

When assessing whether trees may be the ‘root cause’ of damage to a home, several factors should be considered:

Grouping
Trees planted closely together compete for moisture and nutrients in the same soil area. The larger the group, the greater the impact on soil moisture levels in the surrounding area. Consequently, homes or buildings near large clusters of trees are more likely to experience adverse ground conditions due to increased moisture absorption by the trees, leading to greater ground movement.

Distance
The ‘tree-to-damage distance’ guideline from Cutler & Richardson (1989) can help estimate the likelihood of tree-related damage to structures based on their distance from the trees. For instance, the furthest recorded distance a Willow tree has caused foundation damage is 40 meters, suggesting that planting this type of tree at least 50 meters away should be safe. However, it’s advisable to consult an expert if uncertainty remains.

Tree Types
Different tree species exhibit varying activity levels throughout the year, making it important to identify the trees near your home to understand the potential risk to your foundation. For example, deciduous trees go dormant in winter and re-grow in spring, resulting in heightened water demand during dry months, which can exacerbate soil shrinkage.

Characteristics
A tree’s physical traits can influence how much moisture its root system absorbs, but this isn’t always directly related to its size. Research shows that a tree’s leaf area, rather than its height, ultimately determines its moisture demand. Therefore, tall or thick trees aren’t always responsible for dry soil; instead, foliage volume plays a crucial role in indicating water needs.

Surrounding Environment
Infrastructure like roads, pavements, and large developments with limited green spaces can hinder moisture from infiltrating the soil. This lack of permeability can lead to dry soil conditions, prompting tree roots to tap into the scarce moisture, thus intensifying soil shrinkage and ground movement. This scenario is particularly common in urban areas where trees are planted for aesthetics without adequate consideration of soil exposure and moisture availability.

The potential risk of tree roots compromising your property’s structural integrity should not deter you from planting trees or moving to areas rich in greenery. By understanding tree behaviours and their interactions with the surrounding environment, you can effectively manage their influence and minimise the risk of damage to your home or commercial property.

To find out more about non invasive subsidence treatments and for assistance with determining if your property is suffering from subsidence, contact our team of experts.