Building near trees can be tricky. Why? - because trees and other vegetation take water from the soil, causing shrinkage or swelling. If the shrinking or swelling extends below the foundations, this can cause ‘heave’ and lead to property damage.

5 factors to consider when building near trees:

1) Soil type
Soils comprised mainly of clay or fine silt particles can cause problems, whereas soils consisting mainly of sand or with a proportion of clay or silt, are not subject to significant swelling or shrinkage.

2) Tree species
The ‘water demand’ of a tree differs in each species. Trees with a high water demand like Oak, Poplar and Eucalyptus are particularly efficient at exploiting clay soils and rooting to considerable depth. The degree of which the roots extend laterally must also be considered.

3) Tree size
The ‘mature height’ of a tree is important in determining its water uptake which is related to the leaf area and the growth rate of the tree.

4) Proximity of the tree to the foundations
The closer the tree, the deeper the potential influence and the greater the depth required for the foundations. Our Foundation Depth Calculator can be used to determine the exact foundation depth required when building near trees.

5) Climatic conditions
Hot, sunny weather will increase the uptake of water by the roots, whereas rainfall during the summer can restore the water that has been taken. The hottest and driest conditions have the greatest risk, which tends to be in South East England.

If you’re building near trees, take a look at Section 5.2 of our Technical Manual for further guidance and check your foundation depths using our Foundation Depth Calculator.

 

By Frzana Ferguson