Groundworks in Leicester are dominated by trees, and on the Victorian villa plots that is not a small point.
Those plots are deep and were planted generously a century ago. On shrinkable clay, a foundation within influencing distance of a mature tree has to go deeper than the standard depth, sometimes very much deeper, and occasionally the right answer is a different foundation type altogether. The distance that matters depends on the species and the mature height and it frequently extends further than people believe.
There is a less well known risk that runs the opposite way. Removing a large tree from shrinkable clay can allow the ground to swell back over several years, lifting foundations rather than dropping them. Heave is slower and considerably harder to remedy than subsidence, so if a tree is coming out near a proposed extension that belongs in the foundation design rather than being treated as an unrelated job.
Because those trees are protected inside a conservation area, the excavation itself matters as much as the depth. Digging through a root protection area can kill a tree slowly, which is both an environmental and a legal problem, so we hand dig within the root zone where a footprint comes close.
We establish all of this with a trial hole before the design is fixed. Our footings and excavation page explains how we approach foundations and site preparation.