Preventing Subsidence: A Homeowner's Guide

What is Subsidence?

Buying a home is likely to be the biggest single investment you make in your lifetime, and therefore, it is important to understand issues that may be affecting the structure now or at some point in the future.

Subsidence refers to the sinking or settling of the substrate (ground) caused by a combination of natural and/or human-induced activity. The subsidence process can often occur gradually over time (over several years and even decades) or very suddenly, depending on the cause.

Subsidence can have a significant impact on the built and natural environment, as well as the safety of building occupiers and visitors. Subsidence, depending on its severity, can render most domestic properties uninhabitable until they undergo full repairs.

Common Causes of Subsidence

One of the most common causes of subsidence is the withdrawal of sub-surface moisture, such as groundwater, oil, and/or natural gas.

When the ground loses these fluids more quickly than they can replenish, the soil and rock above them frequently collapse, leading to subsidence.

This is known as “compaction subsidence” and is a major problem in areas with heavy groundwater use or fluctuating water tables.

Underground mines and tunnels collapse, another cause of subsidence is the collapse of underground mines and tunnels. Excavation often causes the ground above these structures to settle and move, leading to subsidence.

This can be a significant problem when purchasing property located in old coal fields or close to open mines.

Role of Climate Change in Subsidence

Climate change can also significantly contribute to subsidence. Although further investigation and research in this particular area of study are necessary, it is widely agreed that sea level rises caused by the melting of glaciers and ice sheets, as well as the thermal expansion of seawater, can lead to subsidence along coastlines.

Additionally, changes in precipitation (rainfall) patterns and the frequency and intensity of droughts can affect subsidence through changes in soil moisture and the rate of soil erosion. This is particularly common in sandy and clay-based soils.

Impacts of Subsidence

Subsidence can have significant impacts on the built environment, including damage to buildings, roads, and other infrastructure. In addition, subsidence can lead to flooding and an increased risk of storm damage. The loss of wetlands and other natural habitats can also occur due to subsidence.

Assessing and Managing Subsidence Risk

When purchasing a property in an area at risk of subsidence, it is important to have a survey undertaken to assess the condition of the building fabric and understand any potential risks moving forward.

A thorough survey (such as a Level 3 Building Survey) should be able to identify any signs of active or present subsidence, and any searches undertaken by the Chartered Surveyor should identify any potential risk going forward (such as buying a house on a known coalfield).

Once you purchase a property, several insurance policies cover the threat of subsidence. In this regard, your legal adviser should conduct all relevant searches and advise you accordingly.

Overall, subsidence is a complex problem that can have significant impacts on the built and natural environment, as well as on human health and safety. However, we can minimise and prevent the effects of subsidence by using effective management strategies.

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