What Causes Subsidence in UK Homes and What Does Restoration Involve?

What are the main causes of subsidence?

There are perhaps six main causes of subsidence in UK homes. We’ll look at each below:

1. Clay soil shrinkage

Clay soil shrinkage is perhaps the most common cause of subsidence in the UK. Clay is a highly reactive soil type. It shrinks when dry and swells when wet, leading to inconsistent ground beneath the property. During hot spells, clay soil can contract significantly, pulling the ground away from the foundations.

Properties in some parts of London, the South East, East Anglia and the Midlands are particularly vulnerable.  With the ongoing concern of climate change, this problem could become more common.

If trees or shrubs surround the home, this problem can be made even worse as all the moisture can be sucked from the soil.

If you are concerned about the soil your house is built on, you can use a Geology viewer to see whether your home might be built on soil prone to shrinkage.

2. Nearby trees and plant life

Trees near a building can cause significant subsidence too, and as mentioned earlier, cohesive soils such as clay can be among the worst when there is a great deal of greenery nearby. The roots pull large amounts of moisture from the ground, causing soil to shrink and destabilise. An oak tree, for example, can absorb 1,000 litres of water a day!

Some people think simply removing the tree may eliminate the risk of subsidence, but unfortunately, it’s not the case. When roots die, the moisture they held remains in the soil, which can then swell and cause what’s known as heave. This pushes the foundations upwards, causing you similar problems to if the tree were left in place.

The type of tree also plays a part. Some trees need to be far from the property to minimise subsidence risk.

3. Leaking drains and water mains

Underground leaks are a big problem and are often overlooked. A leaking drain or water main can gradually wash away or soften the soil beneath the foundations. This reduces their load-bearing capability and can cause the house to start to subside.

This is particularly problematic when a home is built on sandy or gravel soils, as they are vulnerable to being washed away. To help reduce this possibility, a regular inspection of gutters, drains and pipework is recommended.

4. Shallow and poor quality foundations

Older homes, especially those built before modern regulations came into effect, were often constructed on shallow foundations. Now insufficient for the loads placed upon them, it can become much easier for the property to lose some stability. This issue can be further exacerbated by adding an extension or loft conversion.

5. Mining activity

Areas previously used for mining carry a subsidence risk. Even if mining ceased in the area many years ago, there is still the risk of old mine workings collapsing both today and in decades to come.  When this happens, there can be significant ground movement that then results in damage to properties on the ground above.

This can be prominent in the Midlands, South Wales, Yorkshire and the North East. Before buying a home in a former mining area, a coal mining search through the Coal Authority is advised. Existing mining subsidence issues have claims handled through the Coal Authority, not your regular buildings insurer.

6. Extreme weather

Extended dry spells can accelerate soil shrinkage, while periods of heavy rain can destabilise some soils. With the UK having such variable weather, the risk of subsidence may only increase as our climate starts to fluctuate more wildly. This means that properties that were previously low risk can now find themselves vulnerable as ground movement becomes more frequent.