What causes subsidence?
There are a vast number of factors that can cause damage to a property from subsidence, heave, or settlementin particular, and it will be difficult to list them all on one page, but some of the most common are discussed below.
What causes subsidence?
Getting a good understanding of what causes subsidence allows you to protect yourself from future claims, or a bad investment if you’re buying property.
Shallow or poorly laid foundations – This is more common in older properties, and it wasn’t until 1976 when Building Regulations made it a requirement to put measures in place to make sure that a property is stabilised. Some of the best examples of these are Victorian and Edwardian era properties built on clay subsoil around London, where it is said one in fifty properties.
This can also occur when adding to an existing building, such as a porch, extension or conservatory. If the new additions are built with shallower foundations than the main house, then the two structures are likely to be affected in different ways (sometimes referred to as differential movement). This can cause them to move apart from each other, and crack at the point where the two buildings meet.
Underlying soil drying out or shrinking over time – This is most commonplace in areas of the country with clay subsoil. A particularly dry summer can cause this to happen, and there is very little that can be done to prevent it, but this is most often associated with trees and vegetation. It is worthwhile having a tree surgeon visit your property to check your trees and the extent of their root systems, as they will often be able to make recommendations as to how to prevent damage to your home, such as reducing or maintaining the height, or removal in extreme cases.
Natural geological events, such as earth tremors – Extremely rare in the UK, but it can happen! This can cause movement to the ground very similar to the subsidence, heave or landslip, and so the same kind of damage can occur.
Human geological events, such as mining and excavation – Insurers pay particular attention to properties located in areas of the UK where mining used to take place. Historically vibrations from mining works themselves may have caused damage to houses nearby, but nowadays the risk comes from the collapse of former mineshafts having a sudden impact to surrounding subsoils. The Coal Authority took over the management of mining related subsidence claims in 1994, and are a great resource for providing information on historic subsidence cases that they handled, as well as offering a range of reports to potential and current home owners.
Erosion of the subsoil – Some watercourses that run underground, such as streams, may shift their course over the years, which can bring them into the path of nearby properties. Also cracked and leaking pipes can cause a discharge of water into the soil which can physically wash away the foundations of a house over time, weakening them, and making them more susceptible to other causes of movement in the future.
Trees and vegetation – New trees, or trees that have grown in height over the years, can start to extract too much moisture out of shrinkable subsoils, with the biggest impact coming in clay soil areas. Conversely, removing a large tree that has been in place for a number of years and doing no harm to a property may cause swelling, heave, and again damage to a home. Tree roots can also be a culprit for damaging pipes and drains, which can lead to erosion as referred to above. Regular monitoring and maintenance is recommended to keep your trees in a position where they won’t affect your home, or your neighbours.
Need some more information?
Why not read one of our other subsidence insurance guides?
- Subsidence Insurance
- What is a Certificate of Structural Adequacy?
- Subsidence, heave, landslip or settlement?
- Spotting the signs of subsidence
- What to do about subsidence
- Subsidence in mining areas
- Subsidence in London – Case Study
- What to disclose to insurers regarding subsidence?
- How insurers underwrite subsidence risks
- Subsidence insurance FAQs
- Subsidence Guide