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TREE ROOTS

TREES rely upon their roots to provide stability, take up moisture and nutrients and to store food. Some building defects are blamed on tree roots but the reality is that few real difficulties arise directly from root damage and those that appear to are usually the result of some other failure or lack of proper maintenance.

Here are a number of popular misconceptions:-

· "Tree Roots go down as far as the tree goes up" - Not True.
Generally tree roots spread horizontally to a distance and depth dependent upon ground conditions. Very few trees have a 'tap root'. The roots require oxygen and water to survive and therefore need to remain close to the surface. 90% of tree roots are to be found in the top 600mm of soil.
Roots may however extend horizontally as far as the tree is tall.

· "Tree roots seek water" - Not True.
Roots need moist soil to grow in. They will stop growing when they reach a dry area. As tree roots cannot detect water they cannot detect water in a pipe.

· "Roots damage drains"- Not True.
The Incidence of tree roots actually breaking drains is very rare. It is far more likely that old drains close to the base of trees could be damaged by the tree movement itself. Dampness around drains caused by leaks or condensation will provide a moist environment such that roots can sheath a pipe but this is generally harmless. Failed pipe joints can however be a means for roots to enter pipes and eventually this may lead to pipe failure or blockage.

· "Tree roots damage foundations"
Tree roots can contribute to damage but are unlikely to be the sole cause of damage. They can contribute both directly and indirectly.
DIRECT tree root damage is often seen at the base of trees where the root/trunk junction occurs and as the roots thicken over time this can damage adjoining walls, footpaths etc. However these are relatively light structures and full domestic foundations are not usually affected; the roots adapting around the foundation. Therefore trees can exist quite happily very close to buildings.
INDIRECT tree root damage is generally the result of moisture abstraction especially on soils such as clay which shrink when dry and swell when wet. This will occur in any event and the presence of trees may have some contributory effect as root systems adapt to changing ground conditions.

· "The only safe thing to do is remove the tree" - This may not be a very good idea. The tree is extracting moisture which if not removed could then cause ground heave of greater damage to adjoining structures. Ground heave is generally more damaging than subsidence.

REMEDIAL ACTION

If trees are suspected of causing or contributing to a structural problem the first thing to do is obtain a specialists advice. The true effect of the trees must be determined before more purposeful action is taken. Seasonal movement for example might be offset by a careful pruning regime.
Tree root effects upon drains will only properly be overcome by replacing old drains with new materials that prevent water seepage and hence root proliferation.
New structures can be designed to avoid the risk of encouraging root growth and to make provision for roots to pass around and through lighter structures. Advice should be sought from your Local Authority Tree Officer or Building department.

BRITISH STANDARD INFORMATION

British Standard BS5837:2005 Trees in Relation to Construction