Few things strike fear into homeowners’ hearts like subsidence. Saying this ‘S’ word out loud even sounds reminiscent of a hissing pantomime villain!
The reason for all the fuss is that subsidence is one of the most dramatic and destructive types of structural movement in buildings, often resulting in a massive bill to remedy the problem. The good news is that home insurance policies cover subsidence damage. Unfortunately they also have a multi thousand pound excess clauses (ie you normally have to pay the first 2 or 3 thousand pounds). Also it can drag on for ages because insurers usually take many months (sometimes years) to satisfy themselves it really is subsidence. They also tend to exclude cover from things like poorly built lean-to conservatories. Leaving an issue like this to develop WILL impact the value, and ultimately the sale price, of your home.
First signs usually take the form of persistent and growing cracking in the main walls.
Cracks naturally worry homeowners, but there are several other causes, such as settlement, differential movement, or thermal expansion, which are not usually so serious.
All buildings move to some extent and older houses with shallower foundation tend to move a lot more, as the ground shrinks and swells in line with the seasons. Clay ground is especially prone to moving – shrinking with summer droughts then swelling with winter rain and frost. This is made worse by the presence of big thirsty trees with extensive roots sucking out moisture.
What exactly is subsidence?
Subsidence refers to the support underneath foundations (or older footings) disappearing.
Imagine if the floor underneath the chair that you’re sitting on right now suddenly collapsed, then you would subside downwards. Contrast this with settlement where the ground very slowly compacts under the building over time, like a fat person sitting on a firm cushion.
So what can cause subsidence to happen in buildings? There are extreme cases where people have decided to excavate illegal basements beneath their homes, removing the ground underneath some of the walls! But more likely it’s due to the ground shrinking away after a long drought (usually exacerbated by trees), or hidden drainage leaks over time causing the ground under the walls to become soft and marshy.
What should you do when cracks appear?
The fact is, most cracking is not subsidence-related. An old rule of thumb is if you can get a £1 coin into the crack it’s more likely to be serious! So it needs to be a sizeable crack. Other indicators include the cracks extending up from the ground (below damp proof course level on the lower walls) and the cracking being visible on both sides of the wall, inside and outside. Subsidence cracks tend to be diagonal and wider at the top.
If the cracking persists for several months, the best advice is to get a structural engineer’s report. This shouldn’t cost too much, and will advise you whether it’s worth making an insurance claim. To see a range of surveyor’s quotes at low prices for free we recommend you click here