Not all subsidence can be prevented — geology and weather are beyond your control. But the practical steps in this guide address the factors that are within your control, and collectively they can make a significant difference to your property's risk profile.
These recommendations come from patterns we've observed across hundreds of subsidence repair projects in Hertfordshire.
1. Manage Trees and Vegetation Properly
Trees are involved in the majority of clay shrinkage subsidence claims. The key is not to avoid trees entirely, but to manage them intelligently.
Planting distances: As a minimum, keep new trees at least as far from the building as the tree's expected mature height. For high water-demand species (willow, poplar, oak), increase this to 1.5 times.
| Tree Type | Safe Minimum Distance from Building |
|---|---|
| Willow, Poplar | 1.5× mature height (25–40m) |
| Oak, Ash, Elm | 1× mature height (20–30m) |
| Birch, Cherry, Apple | 0.75× mature height (8–15m) |
| Hedges (privet, laurel) | 3–5m |
Existing trees too close? Don't remove them without professional advice — removal can cause heave on clay soils. Crown reduction (reducing the canopy by 30–50%) is usually safer and can be repeated every 3–5 years.
Hertfordshire context: The garden city heritage of Welwyn Garden City and Letchworth means many properties have large, mature trees planted close to buildings. These often need proactive management.
2. Maintain Your Drainage
Leaking drains are the second most common cause of subsidence after clay shrinkage. Water escaping from broken pipes washes away fine soil particles beneath foundations, creating voids that cause settlement.
What to do: - Have drains CCTV-surveyed every 5–10 years, or immediately if you notice slow drainage, gurgling, or damp patches - Fix cracked or collapsed sections promptly - Ensure all downpipes are properly connected and discharging into drains — not just soaking into the ground next to the building
Particularly important in: Hertford, Ware, Hoddesdon, and other river valley towns where alluvial soils are easily washed out.
3. Keep Gutters and Downpipes Clear
This is the simplest, cheapest measure — and one of the most effective. Blocked gutters overflow and pour water directly next to your foundations. On clay soils, this creates localised swelling on one side of the building while the other side remains dry.
Clean your gutters at least twice a year (spring and autumn). Check that all downpipe connections are intact and water flows freely to the drain.
4. Avoid Unplanned Excavation Near Foundations
If you're planning landscaping, a new patio, or an extension, think about what excavation will do to the ground near existing foundations. Digging even a metre deep alongside a foundation can remove the lateral support that prevents sideways movement.
Rule of thumb: Don't excavate within a 45-degree angle from the base of any foundation without consulting a structural engineer.
5. Monitor Cracks Proactively
Small cracks are normal in most buildings. What matters is whether they're changing.
How to monitor: Mark both ends of each crack with a pencil and write the date. Alternatively, bridge the crack with a strip of card fixed with tape on each side — if the card tears, the crack is moving.
Check every 2–3 months. If cracks widen by more than 1mm over a season, or continue growing consistently, it's time for a professional survey.
6. Improve Ground Drainage Around the Building
Water pooling next to your foundations is never good. On clay soils it causes localised swelling; on sandy or chalky soils it can wash out the ground.
Options: - Ensure the ground slopes away from the building on all sides - Install French drains or channel drains along problem areas - Avoid paving right up to walls — leave a gravel margin that allows controlled drainage - Don't over-water gardens immediately adjacent to the house
7. Consider Proactive Ground Stabilisation
If your property is on high-risk clay soil and you're seeing early warning signs, proactive resin injection can stabilise the ground before damage becomes serious. This is increasingly common for:
- Properties about to go on the market (avoids complications during the sale)
- Properties with a subsidence history where the owner wants to prevent recurrence
- Buildings near large trees that can't easily be removed
Proactive stabilisation typically costs less than reactive repair, because the ground hasn't deteriorated as far.
When Prevention Isn't Enough
If you're already seeing warning signs despite good maintenance, don't delay getting professional help. Early intervention is always less costly and less disruptive than waiting until the damage is severe.