25 Feb, 2024

The Problem: Building near trees can be advantageous for various reasons, such as increased property value and natural shade. However, it introduces unique challenges, particularly regarding soil stability. Two critical factors come into play: soil with shrink/swell potential and the presence of trees within a certain proximity to the building.

Soil Conditions: For soil to be affected, it must have shrink/swell potential. Pure gravels or sands are less susceptible, but proximity to large trees can still pose risks. The foundation of a house relies on the soil, and if it undergoes volume changes, it can destabilise the building.

Understanding Shrink and Swell

Shrink: As trees grow, their roots absorb moisture from clay soil, causing it to shrink. This often occurs unevenly, leading to twisting and cracks in foundations.

Swell: Conversely, when a tree is removed or its roots disturbed, the soil may expand or swell. This can be particularly problematic if swelling soils are confined within the structure of a new building.

Soil Types Matter

Clay Soils: Not all clay soils behave the same way. Some, like kaolin, are stable, while others, like montmorillonite, undergo significant volume changes. Even a small percentage of clay in the soil can influence its behaviour.

Quick Soil Test: A simple test involves squeezing a handful of soil. If it sticks together like clay, it indicates its clay-like behaviour.

Understanding Trees

Water Demand: Not all trees have the same water requirements. Some, like Cypress and Oak, have high water demand, while Birch and Holly have low water demand.

Solutions and Precautions

Pruning and Removal: For existing trees, pruning or removal can prevent damage. However, removing a tree can lead to rapid soil swelling, requiring caution.

Foundation Depth: When building near trees, the foundation depth may need adjustment. For instance, a Cypress Leyland planted 3.00 meters from a proposed foundation may require a depth of 2.3m, considering soil characteristics.

Structural Engineering: Structural engineered foundations, such as piles or rafts, might be necessary in areas with numerous trees and shrink/swell conditions.

Clay Board: Using compressible clay boards in foundations exceeding 1.5m depth minimises damage risk in case of soil swelling.

Conclusion: Building near trees offers benefits but requires careful consideration of soil and tree characteristics. By understanding these factors and implementing appropriate solutions, we can ensure stable and lasting structures amidst the beauty of nature.