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Subsidence prevention tips

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Given the extent of damage likely to be caused to any property you own and the high cost of putting it right if it takes hold, prevention is many times better than cure.

Even if your home insurance policy includes subsidence insurance, a major claim is going to raise the cost of premiums you pay in the future and is in any case likely to attract an excess of £1,000 or more, so it is clearly a problem to be avoided if at all possible.

So, here are a few tips and suggestions for subsidence prevention:

Why subsidence occurs

  • in order to take effective preventative measures, it helps to understand what causes subsidence;

  • the most common cause is the shrinkage or swelling of the ground bearing the weight of the property’s foundations as the moisture content of the soil falls and rises;

  • by far the most common reason for this change in the moisture content is the presence of trees and large bushes – and their root systems, in particular – near to the property;

  • during periods of sustained dry weather, such trees and bushes send out their roots further and further in the search for that water;

  • yet the removal of the same trees and bushes may also create a void into which the water table rises, causing the ground to swell, so causing the potential for subsidence for the opposite reasons;

Prevention

  • the key to preventing subsidence, therefore, lies mainly in controlling sudden or sustained changes in the moisture content of the ground bearing the foundations;

  • this is important in both clay soils, where variations in the moisture content leads to shrinkage, and in sandy and chalky soils where excessive water content may wash away the ground;

  • trees and bushes are among the major culprits when it comes to these variations, so their growth needs to be carefully controlled – and much depends on whether the trees in question where growing there before or after the house was built;

  • if the trees were planted after building works, for example, they may be removed or re-planted elsewhere;

  • if the trees are older than the building, removal may cause problems that it solves because of the void created by the dead and dying root systems, so their further growth needs to be controlled by pruning or pollarding to reduce the area of foliage (grown by absorbing water from the soil);

  • in these situations, removing the trees is likely to cause a swelling of the ground as water fills up the void, so leading to the possibility of subsidence through heave;

  • if the trees or large shrubs are the other side of your boundary – in a neighbour’s garden or on council-owned land – you may need to negotiate their consent for the way in which the problem is tackled;

  • clearly, you must not remove or lop trees on which there is a preservation order unless you have the relevant consent;

  • in any event, you might want to call in professional advice – from a tree surgeon, for example – about ways of tackling trees and other plant growth you fear may be posing a threat;

  • swelling of the ground and the consequent risk of heave may be caused by blocked drains, soakaways or rainwater goods, or fractured water supply pipes, so ensure that these are all in a good state of repair.

If problems are being caused by subsidence, they are unlikely to get any better if left alone, so early action – with the help of your insurance company and the relevant professionals – is essential.

Further reading: Guide to subsidence and subsidence insurance

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