Can a UK subsidence risk map be accurately predicted using Met Office data?

The UK subsidence risk map uses Met Office data and the British Geographical Society (BGS) expertise to provide an accurate picture of locations within the UK where buildings are at increased risk of subsidence.

The type of ground that supports the foundations of a building determines the risk of subsidence.

The BGS considers geotechnical information about the ground in the UK to assess its susceptibility to ‘shrink-swell’ subsidence, where the volume of the soil rises or falls depending on its moisture content. Data about long-term temperature and rainfall patterns are used to accurately predict areas with a higher risk of shrink-swell subsidence and produce the UK subsidence risk map that you can see here:

The map shows areas of the country coloured in yellow and red. If your property or asset is in one of those areas, it could be at a higher risk of subsidence than structures in other parts of the UK where the ground is less impacted by moisture content.

Predictions based on the effects of climate change enabled the production of a UK subsidence risk map for the year 2070. This shows new areas becoming at risk of subsidence and higher density of red zones where subsidence is ‘highly likely’. To put this into perspective, the projections suggest that more than 3% of UK properties could be affected by 2030 and nearly 11% by 2070.

The higher risk areas shown on the UK subsidence risk map indicate where clay rich soils are. Due to the cohesive nature of clay soil, it will expand and contract as it absorbs or loses moisture. If the clay soil expands, the ground can rise, known as ‘heave’. With moisture loss, the reverse happens, and the ground shrinks, which can result in subsidence.

The top cause of subsidence, accounting for around 60% of insurance subsidence claims in the UK, is root induced clay shrinkage, where tree roots will remove water from the clay. This is exacerbated during hot, dry summers when the tree roots absorb water from further afield. If the roots reach areas of clay rich ground that support the building foundations, this will increase the risk of subsidence as they remove the moisture and cause the ground beneath the foundations to shrink.

As we have discovered, areas with clay soils can suffer an increased risk of subsidence due to shrinking when they lose moisture and recent weather suggests that we could be in for another dry year. Looking back at 2022, as anyone in the UK at the time would testify, the summer was particularly warm. In fact, according to statistics from the Met Office, it was the UK’s fourth warmest summer on record. Temperatures broke the forty-degree mark for the first time on July 19th where 40.3°C was reached in Coningsby, Lincolnshire. Overall, 2022 was the warmest year on record, with the UK’s average annual temperature being more than 10°C for the first time.

This trend has continued into the first part of 2023, after a drier and milder than average winter, the provisional figures from the Met Office show that the UK had its fifth mildest February on record and England had its driest February since 1993.

Source: Met Office – Climate summaries © Crown copyright

Source: Met Office – Climate summaries © Crown copyright

The darker areas on the rainfall maps for both winter and the month of February alone, show areas experiencing the driest conditions mostly towards the south and east of the country. These overlap with the areas of clay rich soil on the UK subsidence risk map, suggesting that the effect of the continued dry weather will increase the risk of subsidence events occurring in these areas.

As Michael Lawson, Chief Executive Officer at Property Risk commented “After an amazing 2022 summer, a dry winter sets us up for an interesting claim environment for 2023”.

If your property or assets are situated in an area of the UK subsidence risk map with an increased risk of subsidence, you can first do some simple checks to see if there are any early signs of subsidence to your structure.

For dwellings or buildings, if you see cracks in the internal and external walls or experience sticking doors and windows, this may indicate a subsidence problem. It is not always the case, as they could be caused by the natural settlement of a building. However, if they are combined with sunken floors, then this will be a stronger indication that subsidence may be present. If you have concerns, then contact a suitably qualified structural engineer. They will be able to conduct a professional evaluation and give recommendations as to the steps that can be taken to correct any existing subsidence issues.

For industrial buildings and infrastructure, cracks, and sinking or uneven surface is the first sign of unstable land or ground that has been compromised. Geotechnical or structural engineers will be able to ascertain the extent of the issues and offer remedial ground strengthening solutions that are most appropriate for the project.

Traditional options available to fix existing subsidence, such as underpinning and especially piling, can be disruptive, time-consuming and costly. However, there are alternative techniques that are quick and non-intrusive and can be deployed. If you are in a higher risk area of the subsidence risk map and need help now or in the future, these new methods can rectify subsidence smoothly with minimal disruption.

Mainmark offers the Teretek® resin injection solution. This is a modern way to deliver both ground improvement and re-levelling of residential properties in a fast, economical, and non-invasive process backed by a 20-year product warranty.

If you have a particular concern about subsidence and would like to talk through your options, please get in touch with us, and our team will be happy to offer their support and guidance.