When the ground under a property falls in level it causes the foundations to shift downwards. As a result, there is pressure on the building’s structure which is why cracks appear. The commonest chain of events is that the soil shrinks, tree roots absorb too much water and drains and pipes start leaking causing the ground surrounding the property to become softer. This weakens the foundations’ ability to bear weight, with the resulting downwards movement of the foundations.
Subsidence can happen anywhere but some areas are more susceptible due to the soil type. These include clay, silt, sand and gravel soils. Clay and silt are ‘cohesive’ soils, which means that their volume will vary depending on their moisture content – they’ll swell when wet and shrink when dry. 75% of UK ground subsidence cases are caused by soil shrinkage, so if you live in a clay soil area then you are more likely to be at risk. With the recent speight of intensely hot and dry weather we’ve had this year, these soil types have been even more susceptible to shrinkage.
In the UK, London is a particular hotspot for subsidence. Most properties in the Greater London area are built on London Clay, which is one of the most shrinkable soil types of all as it’s highly susceptible to changes in volume caused by high water content. In fact, London has the highest ‘shrink-swell clay hazard’ in the country. Areas within London most likely to be affected include most of the North London postcodes and the areas most likely to be affected in Hertfordshire include St Albans, Hatfield and Potters Bar.
If you notice any recent cracking to walls, ceilings or outside brickwork, or you notice that existing cracks have opened up or doors and windows are sticking this could be the early stages of subsidence. As experienced Chartered Surveyors and Engineers, we have the expertise to identify whether these cracks have been caused by subsidence or not. We can often confirm whether subsidence is present on the basis of a single inspection. If we believe the property shows signs of progressive subsidence we can advise you on the best course of action. We have offices in North London and Hertfordshire and for further advice please contact our North London Office on 020 3633 0088 or our St Albans, Hertfordshire Office on 01727 613088.