Guide to Tackling Subsidence
Subsidence is a word that strikes fear into the heart of any homeowner. At its worst, it can be a major safety hazard, yet if the signs are discovered early enough, it is possible to prevent the need for expensive remedial work. Let’s look at what subsidence is, what causes it, what you can do to protect your home and what foundation repairs can be done to fix it.
What is subsidence?
Subsidence occurs when the ground underneath a property begins to shrink or collapse. This causes the building’s foundations to become unstable and move. Clay soil is particularly prone to shrinking following a spell of dry weather. Tree roots are a major cause of subsidence as they remove significant amounts of moisture from the soil. Water leaking under a building can wash away the soil from the foundations, particularly if it has a high gravel or sand content.
What are the signs of subsidence?
Research from the UK House insurer LV highlights that 51% of homeowners don’t know what the signs of subsidence are. Furthermore, almost one in five homeowners have noticed potential signs of subsidence, yet 26% of those didn’t take any action!
The most common signs of subsidence affecting a domestic dwelling are:
- Large cracks in walls, both indoor and outdoor
- Diagonal cracks appearing at the edges of windows and doors. These are often wider at the top than the bottom and around 3mm thick
- Doors or windows that are difficult to open or stick for no reason
- Tearing wallpaper which is not caused by damp
- Dips in a path or drive, especially if they seem to deepen in dry weather or change over time
Whilst it is important to be vigil, not every imperfection is a sign of subsidence. Minor cracks are often caused by ‘settlement’ which is where a building compresses slightly, due to its own weight. Temperature changes also cause buildings to swell and shrink over time, which can cause minor cracks. Dampness and mould are far more likely to be caused by ventilation issues.
What are the risk factors for subsidence?
When it comes to subsidence, not all buildings and areas are at the same risk. The main risk factors are:
- Large trees or shrubs planted too close to your home can cause subsidence as the root structure drains the moisture from the soil. Estimates suggest around 70% of all subsidence cases are caused by tree roots
- Clay soil can shrink when the weather is hot and dry
- Drought prone areas can dry out soil, which increases the chance of ground shrinkage
- Leaking drains, gutters and water mains can soften and erode soil, again causing shrinkage
- Older properties may have shallow foundations, which can increase the impact of any soil movement
- Historic mining activity can be an issue if your house has been built near a former quarry or pit. Coal Authority maps can help you find out if your property is in such an area
If early signs of minor subsidence are detected, it is possible to take remedial action to prevent further damage from occurring. Depending on the cause of the early signs, three effective steps you can take are:
- Pruning trees and large shrubs to help prevent soil from drying out and shrinking
- Checking water pipes, drains and guttering for leaks which might cause soil erosion or one part of the soil to become significantly wetter than another
- Ensuring there is a sufficient area of porous surface, such as gravel or grass, to allow water to drain naturally and evenly
Make sure that when you plant new trees, you consider how much moisture they will consume once they are mature and don’t plant them too close to existing or planned buildings.
Dealing with subsidence
If you think you have subsidence, the best course of action is to inform your insurance company. They will be able to arrange an appropriate survey to quantify the damage and suggest a course of action. Where subsidence is present, there are two likely solutions, underpinning or resin injections.
Steel underpinning can be used to raise, relevel, and then support the building. This is significant work likely to cost anywhere between £10,000 and £75,000 depending on the size of the property and the extent of the damage.
Our advice is always to act quickly if you think subsidence might be an issue, the problem never solves itself! Good luck and please give us a ring on 01380 850885 if you need advice or help.