That Sinking Feeling: Guide to Subsidence

Ask any homebuyer which word they dread seeing most in a Surveyor’s Report and you usually get the same answer ‘subsidence’. While subsidence can cause very real problems, it’s a term that’s little understood, and there’s usually something that can be done about it.

What is subsidence?

The online Oxford Dictionary defines subsidence as ‘the gradual caving in or sinking of an area of land’. And if that ‘area of land’ happens to be underneath your house; then you could be one of the 30,000 people affected by subsidence each year*.

What are the causes of subsidence?

Subsidence is most commonly caused by fluctuations in ground water which causes the soil to contract. Nearly three quarters of all subsidence claims are for properties built on clay soils, which means that the South East is hit harder than any other part of the country.
Clay is a particularly porous soil which shrinks when drying causing household foundations to shift. So while the prospect of long-hot summers is welcomed by the British public, the insurance industry is bracing itself against the effects of global warming.

Prolonged dry spells have a marked effect on the level of the water table, but surprisingly it’s the local flora that does the most damage. Which? magazine estimates that trees and bushes sucking up more than their fare share of water cause 70% of subsidence. Particularly thirsty trees to look out for include: ash, oak, willow and poplar.

Leaking drains and broken water mains are responsible for a further 20% of subsidence claims. However, this time it’s escaped water washing away sandy and gravely subsoil that causes the damage. The remaining 10% of claims are as a result of poorly laid foundations and past mining activity in the area.

What are the signs of subsidence?

Cracks appearing in interior plasterwork or exterior brickwork are the most common signs of subsidence. The trick is to determine whether the cracks are merely cosmetic or are indicative of a deeper structural problem. In cases of subsidence the cracks tend to be wider at the top than at the bottom and can appear suddenly.

If you have any suspect cracks (which are wider than 3mm or the width of 50p piece) get in touch with your insurance company and arrange a structural survey as soon as possible. While urgency is the name of the game; be aware that the cracks may need monitoring for up to 12 months.

Other telltale signs of subsidence include doors and windows sticking without any obvious cause.

How do you treat subsidence?

The good news is that the causes of subsidence are relatively easy to remedy. Subsidence caused by thirsty trees can be solved by pruning or removal. However, it’s important to seek professional help or you could end up making matters worse. Subsidence caused by runaway water can usually be solved by repairing or replacing damaged pipes.

The worst case scenario is that your house will need underpinning, which effectively involves laying a new set of foundations beneath the property. It’s an expensive business, typically costing between five and fifty thousand pounds, and is only used as a last resort.

How does subsidence affect your insurance?

If you are making a first time subsidence claim most standard household insurance policies will payout - once you have covered the excess. However, because claims tend to be expensive; you may find yourself in difficulty when it comes to renewing cover.
Some insurers refuse cover, while others charge sky-high premiums. It’s often ‘suggested’ that you won’t be able to find cover elsewhere, but take any such advice with a large pinch of salt and don’t be forced into a financial stranglehold.

The best advice is to find a broker with a proven track record for insuring properties with ‘a history of ground movement’, and don’t be afraid to shop around. Price comparison websites tend to shy away from offering subsidence insurance due to the complicated nature of cover.

A final word

Arranging subsidence insurance cover is just as much of an art as it is a science. You’ll need to carefully balance the level of excess with the price of the policy. After all, it’s better to have an affordable quote with increased subsidence excess than an expensive quote... or no quote at all.

*The Association of British Insurers (ABI) reports approximately 30,000 new subsidence insurance claims each year.


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