What is clay shrinkage subsidence?

Many parts of the UK, particularly London and the South East, are built on clay soil. Clay is a unique material that acts like a sponge: it swells in volume when it absorbs moisture and shrinks when it dries out.

During warm, dry summer months, the moisture content in the clay is reduced, causing the ground to shrink and lose volume.

This shrinkage can cause the foundations of a house to sink downwards, leading to subsidence. When the wetter seasons return, the ground swells back up, potentially pushing the foundations upwards. This cycle of up-and-down movement is what causes structural damage over time.

What causes clay to shrink?

Two main factors work together to draw moisture out of the ground and cause clay shrinkage:

External view from pavement of row of terraced homes with trees on the left side of the pavement and shrubs on the right

1. Trees and large shrubs

Trees are the single biggest contributor to clay shrinkage subsidence. The root system of a large, mature tree can draw out hundreds of litres of water from the soil every day. If a thirsty tree is planted too close to a property on clay soil, its roots can cause significant and localised drying of the ground, leading to foundation movement.

A view of dry cracking clay soil in front of a residential home with a Geobear tech's feet visible.

2. Prolonged dry weather

Long periods without rain, especially during hot summers, cause the ground to dry out naturally. This widespread drying lowers the water table and causes the clay to lose volume over a large area, which can lead to subsidence issues, even for homes without large trees nearby.

View of a curved brick residential wall showing two large stair-step cracks caused by subsidence.

Signs of clay shrinkage

The signs of clay shrinkage subsidence are the same as for other types of subsidence. The key indicator is the timing: are the problems worse or more noticeable at the end of summer or after a long dry spell? Look out for:

The Solution:

Improving the Ground

In the past, the solution often involved cutting down the trees causing the issue. Today, there is a better way.

Geobear’s clay shrinkage treatment uses a geopolymer injection method to solve the problem at its source without harming the local environment.

Before any work begins, we conduct a thorough soil investigation to understand the depth of the clay, its moisture content, and the extent of any tree roots.

Our expert team then injects the geopolymer material into the ground, often below the deepest tree roots. The material expands to fill any cracks and fissures in the soil, creating a strong, stable barrier that prevents moisture from being extracted from the clay.

This provides a long-term solution to the damaging shrink-swell cycle.

The work is typically completed in just one or two days, with no excavation and no need to move out.

3D illustration of Geobear's clay treatment showing injection points, exposed residential home foundation, and clay soil with tree roots.

 

How climate change and soil desiccation increase subsidence risk

The link between our changing climate and the risk of subsidence is becoming clearer every year. Hotter, drier summers are having a direct impact on the clay soil beneath millions of UK homes, leading to a process experts call soil desiccation.

View of dry, cracking clay soil with a little green grass on the edges. Deep cracks are visible in the soil.

What is desiccation?

Desiccation is the scientific term for the severe drying out of soil. Think of the clay under your home like a sponge: it swells with moisture in the winter but shrinks dramatically during prolonged dry spells. As the ground loses its moisture during a hot summer, this desiccation causes the clay to crack and shrink in volume. When this happens, the ground can no longer properly support your home's foundations, causing them to sink.

This isn't just a current problem; it's a growing risk.

The British Geological Survey warns that as climate change leads to more extreme weather, soil desiccation will become more severe and widespread. They project that by 2070, millions more British homes will be at risk from clay shrinkage, especially in areas of the country that have rarely seen the issue before.

Geobear tech carrying tools walking along city pavement to a Geobear vehicle.

 

END THE SHRINK-SWELL CYCLE

Get a lasting solution for your home

Our clay shrinkage treatment is a fast, non-disruptive way to solve the problem at its source. We can improve the ground beneath your home, often in just a single day, without excavation or needing to remove beloved trees.

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