After two consecutive years of exceptionally warm and dry weather, subsidence has become an increasingly important concern for British homeowners, insurers and structural engineers. But why does drought affect building foundations, and what engineering solutions are available when ground movement occurs?
The answer lies in the interaction between soil moisture, ground characteristics and the loads transmitted by buildings to their foundations.
Understanding these mechanisms is essential to selecting an effective and proportionate repair strategy.
What Is Subsidence and Why Does It Occur?
Subsidence is the downward movement of the ground supporting a structure.
When movement occurs beneath a building’s foundations, it can lead to uneven settlement, structural deformation and cracking.
The causes of subsidence vary considerably and may include:
- Shrinkage of clay soils during prolonged dry weather.
- Moisture extraction by trees and vegetation.
- Leaking underground drainage and water supply systems.
- Erosion or washing out of fine soil particles.
- Poorly compacted or unsuitable made ground.
- Changes in groundwater conditions.
- Inadequate ground-bearing capacity.
Identifying the underlying mechanism is fundamental because different causes require different engineering responses.
Why Are Clay Soils Particularly Vulnerable to Drought?
Clay soils contain fine mineral particles that interact with water.
Some clays are particularly susceptible to changes in moisture content, exhibiting what is commonly known as shrink–swell behaviour.
During wet periods, these soils can absorb moisture and expand.
During dry periods, water is lost and the soil contracts.
Where foundations are supported by shrinkable clay, changes in soil volume can result in differential ground movement.
The consequences depend on several factors, including the clay’s plasticity, foundation depth, local drainage conditions and the presence of vegetation.
The exceptional summer of 2026 illustrates the importance of this mechanism.
According to the Met Office, England recorded its driest July since records began in 1836, receiving just 6.5 mm of rainfall.
The exceptionally low rainfall, combined with high temperatures and prolonged dry spells, created conditions associated with increased soil moisture deficits.
The Influence of Trees on Foundation Movement
Trees and large shrubs can significantly influence the moisture content of the ground surrounding a building.
Their root systems extract water, particularly during the growing season.
Where trees are located near foundations resting on shrinkable clay, the moisture deficit may become more pronounced in some areas than others.
This can contribute to differential settlement.
However, tree presence alone does not establish the cause of subsidence.
Tree species, maturity, distance from the building, soil characteristics and seasonal movement patterns should all be considered.
Removing a tree without a suitable investigation can also create additional risks, including ground heave as previously desiccated clay recovers moisture.
Any vegetation management strategy should therefore be based on appropriate technical and, where relevant, arboricultural advice.
How Can You Identify Foundation Movement?
Visible cracking is often the first indication that something may be wrong with a property.
Common signs associated with subsidence include diagonal cracks near doors and windows, separation between extensions and the main building, and distortion of door or window openings.
However, not every crack is caused by subsidence.
Thermal movement, drying shrinkage of construction materials, structural deflection and normal building settlement can produce similar symptoms.
A reliable diagnosis may require monitoring over time to establish whether movement is active, seasonal or historic.
For this reason, cosmetic repairs should not automatically be treated as a solution to suspected foundation instability.
Why Ground Investigation Matters Before Repair
A successful foundation repair begins with identifying the conditions beneath the building.
An appropriate investigation should establish:
- The nature and characteristics of the soil.
- The depth and configuration of the existing foundations.
- The likely mechanism responsible for the observed movement.
- The location and extent of any weak or disturbed ground.
- Whether the underlying cause remains active.
Depending on site conditions, a geotechnical assessment may include trial pits, dynamic penetration testing, boreholes, laboratory soil tests and geophysical investigations.
Electrical Resistivity Tomography (ERT)
Electrical Resistivity Tomography, commonly known as ERT, is a geophysical investigation technique used to examine variations in electrical resistivity within the ground.
These measurements can help identify subsurface anomalies potentially associated with moisture variations, changes in soil composition or the presence of voids.
Interpretation requires geological context and, where appropriate, confirmation through direct investigation.
At GEOSEC, ERT-based investigation can form part of the assessment and monitoring process for suitable ground improvement applications.
By combining geophysical information with geotechnical testing, engineers can develop a more informed understanding of ground conditions and identify areas requiring further investigation or treatment.
What Are the Available Methods of Subsidence Repair?
There is no single repair method suitable for every subsidence problem.
The appropriate solution depends on the cause and severity of movement, the ground conditions and the structural requirements.
Traditional Underpinning
Traditional underpinning involves strengthening or extending existing foundations, often by excavation and the construction of additional support beneath the building.
It can be appropriate where deeper or more substantial foundation support is necessary.
However, depending on the project, it may require extensive excavation, structural precautions and considerable disruption.
Ground Improvement Using Expanding Resins
Expanding polyurethane resin injection is an alternative ground improvement technique for selected ground-related problems.
The method involves introducing resin into targeted areas beneath foundations or structural slabs.
Following injection, the resin undergoes a chemical reaction and expands, potentially filling voids, improving contact between soil particles and increasing the stiffness or resistance of suitable ground materials.
Depending on the conditions, the treatment can be performed through relatively small-diameter injection points, limiting excavation and disturbance.
Potential applications include:
- Filling voids beneath structural elements.
- Improving support in certain loose or poorly compacted ground materials.
- Treating localised loss of support beneath foundations or slabs.
- Consolidating selected areas affected by ground deterioration.
However, resin injection is not automatically an appropriate solution for subsidence caused by continuing shrink–swell behaviour in clay soils.
Where seasonal desiccation or vegetation-related moisture changes remain active, the causes of movement must be addressed and the long-term suitability of any ground improvement method carefully evaluated.
Deep Foundation Solutions
Where shallow ground improvement is insufficient, deeper structural support may be necessary.
Solutions can include conventional underpinning or the installation of micropiles, depending on the building and ground conditions.
A properly designed micropile system can transfer structural loads towards more competent material at depth.
The design must account for the existing foundations, structural loads, installation conditions and the required load-transfer mechanism.
GEOSEC’s Approach to Ground Stabilisation
At GEOSEC Ground Engineering Ltd, we believe that successful ground improvement starts with a clear understanding of the problem.
Our specialist ground engineering services are based on combining investigation, technical assessment and targeted intervention.
GEOSEC’s See&Shoot® methodology integrates geotechnical information with controlled resin injection and geophysical monitoring where site conditions permit.
This approach helps the technical team evaluate ground conditions, identify treatment areas and assess changes during the intervention.
Where an expanding resin solution is considered suitable, the objective may be to improve support conditions beneath the affected structure while minimising unnecessary excavation.
The treatment design and verification methods are adapted to the specific engineering requirements of each project.
Why Accurate Diagnosis Is Increasingly Important in 2026
The growing number of subsidence insurance claims has made effective diagnosis and repair planning particularly important.
Figures published by the Association of British Insurers show that the average domestic subsidence claim reached £20,000 in the second quarter of 2026.
For insurers and homeowners alike, selecting an unsuitable repair strategy can result in further investigation, delays and additional costs.
A technically sound approach should therefore prioritise understanding the ground conditions, identifying the mechanism of movement and selecting an appropriate intervention.
The objective is not simply to repair visible cracking but to address the engineering problem responsible for the damage.
Frequently Asked Questions About Subsidence Repair
Can subsidence be repaired without traditional underpinning?
In some cases, yes. Depending on the cause of movement and the structural conditions, alternatives such as drainage repairs, vegetation management or ground improvement may be appropriate. Other properties require structural underpinning or deeper foundation support.
Can resin injection repair subsidence?
Resin injection can improve ground support and fill voids in suitable conditions. Its effectiveness depends on the soil type, cause of movement and treatment design. It is not a universal solution for all forms of subsidence, particularly active shrink–swell clay movement.
How can I tell whether cracks are caused by subsidence?
The location, shape and development of cracks can provide useful information, but cracking alone cannot establish subsidence. A structural assessment and, where necessary, ground investigation or movement monitoring are needed.
Does subsidence always require major excavation?
No. Some cases can be resolved through targeted mitigation or less invasive ground improvement techniques. The appropriate method must be determined by a competent technical assessment.
Can drought-related subsidence return?
Yes. Seasonal moisture changes can cause repeated movement, particularly where shrinkable clay and moisture-extracting vegetation remain influential. Effective long-term repair requires consideration of these ongoing mechanisms.
Contact GEOSEC UK for Specialist Ground Engineering Advice
Structural movement can have several causes, and the correct repair strategy should be based on evidence rather than assumptions.
GEOSEC Ground Engineering Ltd provides specialist ground investigation and improvement services for residential, commercial and industrial applications.
