On a weekly basis, I have to try and explain that peoples’ perception of tree root damage is flawed, and it is not the physical action of a root pushing against a foundation or growing under a foundation that is the most common mechanism of damage. 

In this image, the root of a Silver Birch has met with the back of a kerb edging in a car park.  Compared to a building foundation, which may be a metre deep or more, this is a very light structure, and yet the root has not damaged the kerb or deflected it.  You can see that to the right, the root has become wide and flat, spreading its mass against the flat side of the kerb.  Once over the kerb, it has taken in a more rounded shape but still with a flat underside.  To the right of the kerb, the root is damaging the tarmac because it is a very viscous liquid that offers minimal resistance to the relatively small forces exerted by the root.