While sunny conditions may be welcomed by many, an extended period of exceptionally low rainfall can have significant implications for buildings founded on shrinkable clay soils. The risks are particularly acute in the summer of 2026, with England recording its driest July since records began in 1836.
Conditions have been even more extreme in Southern England, where only 1.9mm of rainfall was recorded, equivalent to just 3% of the seasonal norm, making it the driest month ever recorded in the region. Such sustained drying of the ground, especially during the peak growing season when vegetation is actively extracting moisture from the soil, can increase the likelihood of clay shrinkage and associated movement in building foundations.
If these conditions continue, the UK could face what the subsidence industry refers to as a "surge year", with a significant increase in subsidence-related damage and insurance claims.
This possibility is particularly relevant as climate change continues to alter long-term weather patterns. The Institution of Structural Engineers' Subsidence highlights how warmer temperatures, hotter and drier summers, and increasing soil moisture deficits are expected to influence future subsidence risk across the UK.
Why Dry Weather Creates Problems
Subsidence occurs when the ground beneath a building moves unevenly. In the UK, the greatest risk is often associated with clay soils, which shrink as they lose moisture and expand when rehydrated.
Buildings with conventional strip or raft foundations constructed on shrinkable clay are particularly vulnerable. As soils dry and contract, foundations can settle unevenly, leading to cracking and distortion.
Crucially, a sudden spell of heavy rain is not always enough to reverse the process. Following prolonged drying, clay soils can take months to rehydrate. Intense rainfall often runs off the surface before reaching depths where moisture deficits are greatest.
The Role of Trees
Trees are one of the most significant factors in clay-related subsidence, extracting large quantities of water from the ground during dry periods.
As climate change drives hotter, drier summers, the interaction between trees, soils and foundations is becoming increasingly important. Tree-foundation interactions are likely to become a more common challenge in future, particularly as the benefits of urban greening and increased tree cover are balanced against subsidence risks.
At the same time, the guide emphasises that trees provide substantial environmental and social benefits, including cooling urban environments, improving air quality and supporting wellbeing. The challenge for engineers is therefore to manage subsidence risk while supporting a more climate-resilient built environment.
Valuers advise against indiscriminate removal of trees, as the presence of trees and large bushes add value to an urban environment and property by as much as 20%. Tree management is therefore more important than tree removal. Expert advice is required to assess tree management when reviewing subsidence issues.
Contributing author Tim Farewell said: “Climate change is real, and once more this summer we are seeing serious impacts here in the UK, with thousands of excess summer deaths, cracking houses and damaged critical national infrastructure. Nationally, and internationally we must face up to the reality that if we keep burning fossil fuels, the situation will get worse, and that those least responsible are likely to suffer most.”
The Hidden Risk Below Ground
Drought can create problems beyond shrinking clay soils. As moisture becomes scarce, tree roots may seek alternative water sources, including underground drainage infrastructure.
Older properties, particularly those constructed more than 50 years ago, often have rigid-jointed drains that can be vulnerable to root ingress. Root penetration can cause blockages and structural damage, and damaged drains may later leak, creating further ground instability and contributing to future subsidence problems.
Climate Change and Future Risk
The relationship between weather and subsidence is well established, but climate change is increasing the importance of understanding long-term risk.
Climate-risk specialist Tim Farewell explores in the guide how advances in environmental data science, modelling and analytics are transforming the industry's ability to understand and predict subsidence risk. Tim highlights how climate-adjusted subsidence models are already being used to assess vulnerability to future ground movement and support decision-making across the insurance and lending sectors.
The guide also notes that the Bank of England has required large lenders to consider the impact of climate change on their property portfolios, including the potential effects of subsidence over coming decades.
When a property has been assessed by an expert, and where necessary has been repaired, the Expert is required to issue a Certificate of Structural Adequacy (CSA) providing a professional opinion and outlining what investigations were completed, and crucially what repairs, if any, were required. The CSA should also detail the likelihood of future problems arising from subsistence and potential affects on the building. The Institution of Structural Engineers' Subsidence provides readers with sample CSA’s for reference.
As climate patterns continue to evolve, subsidence is increasingly being viewed not simply as a property defect issue, but as part of the wider challenge of adapting the built environment to future climatic conditions.
Further Reading: Understanding Future Subsidence Risk
The Institution of Structural Engineers' Subsidence (2023 revision) brings together expertise from across structural engineering, insurance, surveying and property disciplines.
An Essential Resource for Climate Adaptation
First published in 1994 as Subsidence of low-rise buildings, with a 2nd edition in 2000, then comprehensively revised in 2023 as Subsidence, the title remains one of the industry's leading references on the subject.
Produced by a multidisciplinary team of experts from across the structural engineering, insurance, surveying and property sectors, it provides authoritative guidance on the causes, investigation and management of subsidence. As structural engineers increasingly respond to climate adaptation challenges, the guide offers valuable insight into the complex relationships between weather, soils, vegetation, infrastructure and building performance. Its coverage of climate-adjusted risk modelling, urban greening and future resilience makes it particularly relevant for practitioners seeking to understand how a changing climate may affect the built environment.
While it remains too early to know whether 2026 will become a true subsidence surge year, the current dry weather serves as a timely reminder that understanding climate-related ground movement is becoming an increasingly important professional competency.
For IStructE members, Subsidence provides a practical and authoritative resource for navigating these emerging risks.
Subsidence
Comprehensive guidance on the identification and rectification of subsidence damage caused by foundation and subsoil movement.
Publish Date – 10 November 2023
Price – £34.95
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