Groundworks in Solihull are decided by trees more comprehensively than anywhere else we work, and it runs in both directions.
The familiar risk first. 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 reaches further than owners believe.
The less familiar risk runs the other way. Removing a large tree from shrinkable clay allows the ground to swell back over several years, lifting foundations rather than dropping them. Heave is slower to appear and considerably harder to remedy than subsidence, and in a borough where trees are regularly removed under consent, it is a genuine consideration rather than a textbook one. If a tree has come out recently near your proposed extension, that belongs in the foundation design.
Then there is the tree itself. Excavating through a root protection area can kill a protected tree slowly, which is both a legal and an environmental problem, so within the root zone we hand dig rather than machine.
We establish all of this with a trial hole before the design is fixed. Everything is inspected before it is covered. Our footings and excavation page explains our approach.