Is my tree causing our house/building to subside?
Trees & Subsidence
Lots of trees are growing near buildings and are not causing any subsidence issues throughout the UK. Building subsidence and structural damage can be caused by many other factors that don’t actually include trees or vegetation in general, including soil type and depth of foundations. Just because there is a tree in situ does not immediately implicate the tree in all instances of building related subsidence. This is why it is important to seek suitable qualified professional guidance to carry out a detailed site assessment to determine the exact cause.
DGS Trees undertake pre-mortgage tree reports and tree related subsidence assessments throughout Southampton and Hampshire. Very often trees are not the culprit where subsidence has or is occurring however on occasions trees are clearly the cause!
A usual reference guide for considering building subsidence can be viewed following this link below:
What is the problem with trees planted and growing near 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.
Trees statutory protection & 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.
Structural damage caused by subsidence
This is generally only a problem on shrinkable clay soils. Buildings constructed before the 1950s are most at risk, as they frequently have foundations only 50cm (20in) deep.
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. Typically newer plastic designed pipes are less at risk, whereas old clay pipes are more susceptible to cracking and leaking.
Physical damage to above ground structures
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 from being physically lifted by growing roots increasing in girth and physically pushing up/lifting foundations.
How can tree roots cause our property 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.
Managing the problem
It is not always the case that removing a tree identified as contributing to subsidence related issues 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 managed 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.
The risk of subsidence related issues can be reduced by not planting larger, vigorous trees such as poplars, oaks and willows near buildings to begin with. See the useful guide below:
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 trees.
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
The following books and publications are useful references for future reading and reaserach;
Tree Root Damage to Buildings by Biddle P.G
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)
The Relationship between Trees, Distance to Buildings and Subsidence Events on Shrinkable Clay Soil
Has Your House Got Cracks? by Freeman, Littlejohn & Driscoll (Thomas Telford Ltd. 1994, ISBN 0727719963)