Tree Root Systems

roots-diagrams

Despite popular misconceptions, tree roots are shallow and may extend well beyond the canopy of the tree. But their ability to damage buildings is often over-estimated

Discussions about street trees often focus on the roots of a tree. Streets Ahead have condemned many trees because of the nature of the roots, some people believe that tree roots may be damaging their property.

This detailed paper by Martin Dobson, of the Arboricultural Advisory and Information Service, describes the nature of tree roots in a very helpful and accessible way.
Dobson (1995) Tree Root Systems

Important points made include these, which are relevant to questions of damage by tree roots:

Tree Roots may extend radially a distance equivalent to at least the height of the tree and are located primarily in the upper 60cm of soil. The main structural roots are usually found in the upper 30cm and taper substantially within about 3m of the trunk. The vast majority of fine absorbing roots are even closer to the soil surface…

…There is considerable misinformation about the damage that can be caused by tree roots. It is true that under some circumstancesthey may cause damage to structures. However direct damage is rare and usually only occurs when trees are situated less than 1-2m away from lightly loaded structures such as boundary and garage walls, paving slabs and kerbs…

…Indirect damage to structures may occur when tree roots contribute to the drying of shrinkable clay soils where foundations are inadequate to accommodate movements…