When a damaged building is founded on clay and roots have been found at or near foundations, it can be considered a certainty that the roots have, in some way, contributed to the damage. There may, of course, be other contributory factors such as uneven soils, under-design of foundations (unlikely in smaller structures), deep seated
lenses of softer materials, and so on. It is not always easy to decide whether the damage has been caused by subsidence or by ground heave, and this writer has come across one block of flats in which one end was affected by ground heave and the other by subsidence. The pattern of cracking will usually provide an indication and the age of the building and the state of the roots will be an additional pointer. It is not possible, in an article of this length, to describe accurately the differences in crack pattern (if it is possible to describe these at all); neither is it possible to give specific advise on where to dig trial holes, the location of these being one of the most important arts in the whole process.
Russell G. Grahame