Trees near buildings

What is the problem with trees and buildings?

Things to bear in mind if you're concerned about trees near houses and other buildings;

• It must be noted that many trees grow near buildings and, in most cases, these will not cause any damage
• However, sometimes trees growing near buildings can cause major problems, especially after a long period of dry weather
• Subsidence is the main problem posed by trees, but there are also the physical threats caused by falling limbs or structural failure of the main trunk
• If you do have a substantial tree near a building or public highway, it is well worth having it professionally surveyed every few years to assess its overall health and to determine any pruning or felling requirements. Ensure that you keep these reports in a safe place, as they may be useful in any negotiations with insurance companies or public bodies

Tree legislation

A tree is the property and responsibility of the land owner, who may be liable for any damage caused. Always check with the Local Planning Authority whether a Tree Protection Order is in place before working on a tree.

Appearance

Structural damage caused by subsidence

• This is generally only a problem on shrinkable clay soils. Buildings up to four storeys constructed before the 1950s are most at risk, as they frequently have foundations only 50cm (20in) deep

Drain damage

• Roots may block drains, which burst as a result. This can lead to the formation of cavities where water flows into the soil. Older drains with poor seals and rigid joints are most susceptible

Physical damage

• Branches can cause damage to roofs and guttering. Suckers can disturb paving, and stems can rub against walls. Buildings of more lightweight constructions, such as garages and sheds, are most at risk

Cause

Just how can tree roots cause problems?

• During prolonged periods of drought, trees can further dry out the soil to the extent that clay soil will shrink. This can result in subsidence and structural cracking, particularly around windows and doors
• Tree roots are unlikely to directly penetrate sound footings, but can exploit any cracks or faults (perhaps caused by soil shrinkage or heave), thereby compounding the problem as they extend and expand
• Tree roots are sensitive to water, and this is what causes them to grow into drains. If the drains are watertight, then tree roots will not generally trouble them

Control

Controlling the problem

• It is not always the case that removing a tree that is contributing to subsidence problems will make the problems disappear. Although the soil usually swells each winter, a permanent moisture deficit can build up under certain circumstances that will result in significant swelling of the soil after the tree is removed and soil gradually returns to its previously moist state. This is called ‘heave’ and can result in serious damage unless it is controlled by careful soil management. Potential heave is very hard to detect and predict. For this reason, professional advice should be sought when large trees are being removed in cases of serious subsidence
• Subsidence can be prevented by not planting larger, vigorous trees such as poplars, oaks and willows near buildings
• Be aware that the extent and spread of tree roots is extremely variable and they are unlikely to grow in a uniformly radial pattern. A useful guideline is that roots can commonly extend a distance equivalent to two-and-a-half times the height of the tree. If unsure about tree choice, always seek professional advice before planting
• Root barriers can be used when planting new trees but, if these are deemed necessary, it is probably better to select a smaller or less vigorous specimen
• Pollarding may help reduce the potential impact of a tree by reducing its further root spread but, before taking steps to remove or reduce in size any tree thought to pose a risk, make sure that it is not protected by a Tree Preservation Order (TPO). Local Planning Authority permission must be obtained before any protected tree is pruned or felled, and similar constraints apply to trees in Conservation Areas
• Be circumspect about removing a specimen that is presumed to be causing a problem. Unless there is an imminent danger from structural failure, hasty action could cause more extensive damage in the future. It is nearly always worth seeking independent advice from a qualified arborist as well as a building surveyor

Root identification: Please note, the RHS is not able to offer a root identification service.

Further reading

The following books and publications make useful reading;

Tree Root Damage to Buildings by Biddle P.G (Willowmead Publishing 1998, Oxford ISBN 095330860X)

The Influence of Trees on House Foundations on Clay Soils (Building Research Establishment Digest 298)

Tree Roots and Buildings by Cutler, D F and Richardson, I B K (Longman Scientific and Technical 1989, ISBN 0582034108)

Precautions to Take When Building Near Trees (The National Housebuilders Standards 1992)

Has Your House Got Cracks? by Freeman, Littlejohn & Driscoll (Thomas Telford Ltd. 1994, ISBN 0727719963)

Some of these books are made available through the RHS Lindley Library.