Common Causes of Subsidence

Subsidence is the movement of ground below a building's foundations. It can cause varying degrees of damage and often result in huge costs and inconvenience (FAQ)

Ground subsidence is a major problem for homeowners. It can happen anywhere, at any time, and for many different reasons. Potential homebuyers and builders should therefore be aware of the possible causes of subsidence in order to avoid future problems.

What Causes Subsidence?
Subsidence is often related to the moisture content in the soil beneath the foundations of a building, and some soil types are more vulnerable than others. There are many natural causes and man-made causes of subsidence.

Natural Causes of Subsidence
Cohesive soils shrinking and swelling
Cohesive soils such as clay or silt can cause subsidence because they shrink and swell according to their moisture content. The weather has a huge impact on the soil's composition, as such subsidence happens in many parts of the UK for this very reason.

Non-cohesive soils being washed away
Non-cohesive soils such as sand or gravel are less susceptible to shrinkage or swelling but are more likely to be washed away with water flow (such as when a pipe is damaged).

Movement in a variety of soil structures
If there are different soil structures underneath a building’s foundations, then their movement can result in subsidence.

Soil decomposition
Ground movement can also be caused by some natural soils like peat and other organic matter decomposing.

Trees and other vegetation
While a nearby bush or tree can add charm to a home, it may also cause subsidence. Because roots soak moisture from soil, vegetation near foundations can cause it to shrink. This is especially dangerous during extended dry periods when thirsty plants push their roots into foundations to find water.

Man-made Causes of Subsidence
Drains that have been damaged
Water can escape from damaged drains and cause ground movement. This problem usually affects sand and gravel-based soils.

Historic mine shafts
Subsidence can be caused by mining in the area, whether past or present, as mine shafts leave unstable ground and thus exacerbate many natural causes of subsidence.

Nearby traffic
A building located near an area of heavy traffic can cause soil movement.

Improper ground preparation
Subsidence can often result from a structure or building built with unsuitable foundations on clay soil that is website compressible.

Construction work
Vibrations and soil movement at nearby excavations can cause negative effects of subsidence.

Poor foundations
Subsidence problems can be caused by poor foundation work, particularly if the foundation has suffered water damage.

Most Common Causes of Subsidence
Of all these causes of subsidence, there are four that are by far the most common.

Clay Soil
The UK's clay soil is formed by the deposition and retention of small rock particles in the sedimentary beds of historical rivers. Clay can retain moisture for decades, even after being removed from an environment such as a river. As it retains more and more moisture it expands. This is a major cause of subsidence in the UK.

Expansion
To some degree all soil compositions shrink and expand underground each year, and this means they go unnoticed. However, the cycle can be disrupted by prolonged periods of drought, which is when things go wrong. An extended dry spell alone will not cause soil shrinkage to the point of subsidence. However, external factors such as human activity and plant life can quickly intervene to bring about major issues.

Tree Roots
Tree roots cause subsidence problems because they branch out to seek moisture in drought situations. This moisture is stored in the soil composition and if the soil is below a building's foundations, shrinkage can occur as the roots reach out in search of moisture. Human negligence can also cause this problem, especially if a building reduces the water a tree can draw from the ground - for example by placing concrete over its roots.

Uneven Ground
Subsidence is more common in the UK west of the Tees Exe line. Here, the geological makeup of the land is rockier. As mine working and unstable ground are likely to cause subsidence this has exacerbated the issue over time. If old mines are not monitored, they can settle to the detriment of properties at the surface. Subsidence can arise from mines running to great depths or far away from an affected site, having a devastating impact on homes in the area.

Building Insurance for Subsidence: How can Frontier Help?
The buildings insurance part of your home insurance policy usually covers subsidence damage to the house itself, however those properties with a history of subsidence can have exclusions against further issues. Most insurers in the market will not cover your home for buildings insurance if there is a history of subsidence to your property.

What Sets Frontier Apart from The Market?
At Frontier, providing the property has a Certificate of Structural Adequacy, we can provide subsidence cover as standard. And you get to choose the excess that applies rather than having one imposed on you.

The average market excess for subsidence is £1000 when you claim for a subsidence event. At Frontier, we see things differently, we therefore do not charge an additional subsidence excess. Always check the Ts and Cs in your insurance policy to understand how you will be charged in the event of a claim.

Leave a Reply

Your email address will not be published. Required fields are marked *