How Trees and Dry Weather Cause Subsidence: A Homeowner’s Guide
If you live in a part of the UK built on clay soils, particularly in the south and east, your home could be at risk of subsidence, especially during long, dry summers. This guide explains the science behind the problem, why certain trees make it worse, and what you, as a homeowner, can do to protect your property.
What Is Subsidence and Why Does It Happen?
Subsidence occurs when the ground beneath a building sinks, causing the structure to move. On shrink-swell clay soils, this is most often caused by the soil drying out and shrinking. During hot summers, two things accelerate this process:
- Evaporation: Water evaporates from the soil surface
- Transpiration: Trees and plants draw moisture from the soil through their roots and release it through their leaves
Together, these processes are called evapotranspiration, and they can remove large amounts of water from the soil, causing it to shrink
How Trees Affect Soil Moisture and Foundation Movement
Tree roots naturally seek out moisture. In dry conditions, they grow deeper and wider, especially in clay-rich soils. Many UK homes have shallow foundations (often less than 1 metre deep), which puts them at risk when deep-rooted trees nearby draw moisture from the soil beneath.
This causes the clay to shrink and the ground to sink unevenly, resulting in cracks in walls, sticking doors, and other structural issues.
Tree Species with the Highest Risk
Some trees have much higher water demands and more aggressive root systems. Here are the top 10 trees most likely to cause subsidence on clay soils:
| Tree Species | Water Demand | Root Spread | Typical Depth | Subsidence Risk | Min. Distance from Buildings |
|---|---|---|---|---|---|
| Poplar | Very High | Up to 40m | 2–3m | Very High | 40m+ |
| Willow | Extremely High | 30–40m | 2–4m | Very High | 35–40m |
| Oak | High | Up to 30m | 3–5m | High | 25–30m |
| Horse Chestnut | High | 25–30m | ~2m | High | 25–30m |
| London Plane | Moderate–High | 20–25m | Moderate | High | 20–25m |
| Elm | High | Up to 30m | Moderate–Deep | High | 25–30m |
| Sycamore | Moderate | 20–25m | Moderate | Mod–High | 20m+ |
| Ash | Moderate | 20–30m | Moderate–Deep | Mod–High | 20–25m |
| Beech | Moderate | Up to 20m | Shallow | Moderate | 15–20m |
| Birch | Moderate | 15–20m | Shallow | Moderate | 15–20m |
What Can Homeowners Do?
1. Manage Trees Wisely
- Avoid planting high-risk species near your home
- Regularly prune large trees to reduce their water demand
- Consider removing problematic trees – but always seek professional advice to avoid sudden ground movement (\”heave\”)
- Check with your local authority if trees are protected
2. Understand Your Soil and Trees
- Use online tools (like Soilscapes) to check if you’re on shrinkable clay
- Measure the distance of nearby trees from your property
3. Watch for Warning Signs
- Cracks wider than 3mm, especially diagonally above windows or doors
- Doors or windows sticking
- Gaps are opening between walls and skirting boards
4. Get Professional Advice Early
- Contact a structural engineer or a specialist subsidence company like Geobear
- Don’t wait – early intervention can prevent costly repairs
5. Check Your Insurance
- Make sure your building’s insurance covers subsidence
- Inform your insurer of any tree management near your property
6. Be Aware of Heave Risk
- Removing a mature tree can cause the clay to rehydrate and swell
- Always get an expert opinion before tree removal
7. Use Geobear’s Free Assessment
Geobear offers free, no-obligation assessments for homeowners worried about subsidence. Our geopolymer injection process can improve ground conditions and remediate subsidence issues without excavation, often in just one day.
In Summary
Hot, dry summers and thirsty tree roots are a major trigger for clay shrinkage subsidence in UK homes. But with awareness, preventative steps, and expert help, you can manage the risk and protect your property.
Need help assessing cracks or subsidence risk? Contact Geobear today for a free assessment.
