Is my tree likely to cause a problem to buildings?
This depends on a number of factors. Gardens on non-clay soils (e.g. chalk or sand) are very unlikely to encounter problems with trees damaging buildings. However, if you are on a heavy clay soil, there is an increased risk. In addition, the larger the tree, the higher the ‘water uptake’ for that species of tree and the closer the tree is to a buildings, the higher the risk too.
How to I find out what the ‘water uptake’ is of my tree?
The book Tree Root Damage to Buildings by Biddle P.G (see Further reading) contains a useful table of tree water uptake, listing trees with the lowest demand (posing the least risk) to the highest demand (posing the most risk). Low water demand trees include; [broadleaved] Catalpa, Corylus, Liquidambar, Liriodendron, Magnolia, Morus, Sambucus, [conifers] Abies, Araucaria, Ginkgo, Larix, Picea and Pinus. High water demand trees include; [broadleaved] Eucalyptus, Populus, Quercus, Salix, [conifers] Cupressus, Chamaecyparis and x Cuprocyparis. Quercus (oak) accounts for the highest number of subsidence cases in the UK. Other species generally have an intermediate water demand.
How far from a tree could problems to buildings be caused?
Tree to damage distance will depend on the type and size of tree. Indications of these distances for some tree species can be found in the book Tree Roots and Buildings by Cutler, D F and Richardson (see Further reading). As a general rule, for high water demand species, expect soil drying influence to extend outwards from the tree to a distance equivalent to the height of the tree. For intermediate and low water demand species influence is unlikely to extend more than half the tree’s height. But remember, other factors contribute to damage occurring and most trees never cause problems for buildings.
Our tree has been identified as contributing to subsidence in a neighbouring property. We would prefer not to lose the tree. Will pruning be an effective solution?
When a specific tree has been found to be the main cause of subsidence having it felled is usually the most permanent solution. However, tree reduction can reduce the amplitude of movement so could be considered as a way to manage the problem. To be effective, pruning needs to reduce the crown volume of the tree by at least 70 percent and be repeated on a regular basis such as every three years. Crown thinning (as opposed to crown reduction) has been found to be ineffective at reducing transpiration rates. Also it should be noted that in cases of permanent deficit (i.e. London clay soils where low permeability leads to deeper permanent drying), felling the tree poses a risk of progressive heave. If there is a risk of significant heave, the only effective solution may be to have the property underpinned (see faqs for Property owners section).
We have been informed our tree is causing subsidence to some newly built houses. Surely we’re not liable for damage as the tree was there before the development. Or are we?
Tree owners are liable for full costs of repairs if a tree is found to be ‘materially contributing’ to that damage. It is no defence to claim the following: the tree was there before the building; the foundations were inadequate; the tree is more valuable than the building; or that as tree owner you were not aware of the risk. Potential defences include trees that have been subject to appropriate management; the presence of clay soil was not reasonably foreseeable (i.e. not marked on a geological survey map); or that there was no remedial action available to prevent the damage such as in cases of heave on persistent deficit soils).
I have just been notified that our tree is causing damage. Can I ignore this? What do I need to do?
Once notified, the tree owner is obliged to do something about it. There are three steps;
- Notify your content insurers for third party liability.
- Interpret available reports (which should be provided at the same time as notification was given – if not, request all reports as the tree owner is entitled to full disclosure).
- If appropriate, take prompt remedial action such as tree felling or reduction.
If a tree has a Tree Preservation Order (TPO) or is in a Conservation Area, does this mean it cannot be felled even if it is damaging buildings?
No. Trees that are covered by some sort of protection such as a TPO can still be required to be felled if they are found to be damaging buildings. However, application for work on such trees usually requires appropriate monitoring and other investigations (see question How is responsibility for subsidence determined? under Property owners faq below) and reports to be made available.
Can wall shrubs and hedges also cause damage?
Yes, potentially. Large wall shrubs, most notably Pyracantha and Wisteria, can caused localised subsidence. Level monitoring will demonstrate which vegetation is most likely to be involved. Tall hedges can also contribute to soil drying so it is advisable to maintain hedges in a subsidence prone area to a height equivalent to the distance of the hedge to the building.
Will putting in root barriers help ensure my tree doesn’t cause damage to buildings?
In theory, yes, but in practise it is usually not feasible to install tree root barriers to sufficient depth. There is also the risk that tree roots will simply ‘follow’ and grow under a barrier since the trenching that is required to fit a barrier also introduces air and water, making an attractive growing environment to roots.
We have old drains and trees growing near to them. Do I need to do anything to prevent the roots blocking the drains?
If the drains are sound (i.e. do not leak) then there should not be a problem and no action is necessary. However, if the old drains leak, this gives opportunity for roots to enter them and potentially cause blockages. So, there are three options. One is to remove the trees but this should only be considered as a last resort. The second is to line the leaky drains with a resin-soaked liner which can prevent roots getting in. The third, and most permanent solution, is to have the old unsound drains replaced with new polypropylene drainage pipes which resist damage from tree roots.
Our patio paving is being lifted by roots from our cherry tree. Can we stop this? Does it mean the roots are also damaging our house?
There is no direct link between damage to non-load-bearing structures such as paving and load-bearing structures such as houses. Most lifting of surface structures such as drives and patios occurs within a 1m radius of a tree’s trunk, corresponding to where the buttress of the trunk base forms. Thus it is advisable not to pave or tarmac within this area (which is also beneficial to the tree). Some tree species, notably Prunus (cherries), have roots that grow very close to the soil surface, making them more likely to lift paving. If damage is localised and at some distance to the tree, the offending root could be cut off, a root barrier fitted to prevent roots growing back into this area and repairs to patios or drives made. Large roots close to the tree should not be cut as these may kill or destabilise the tree.