Subsidence is exactly what its name suggests; it’s when the ground beneath your property starts to sink and drags your home down with it.
The opposite of subsidence is ground heave, which is when the ground underneath your home starts rising.
Neither is desirable as both can cause structural damage to your home, but they are very different and need different courses of action to rectify them.
The causes of subsidence
There are basically three main reasons why homes may suffer from subsidence and it’s useful to be aware of them when looking at properties.
The first is that the property has been built on foundations which are too shallow. This is especially likely with older houses and can also happen if a property is extended upwards without regard to how it will impact the original foundations.
The second is the level of moisture in the area. If the soil below your home gets too dry, it can start shrinking and cracking.
This is particularly likely in clay soil, but, in principle, is possible in any kind of soil. Rather ironically, excess moisture can also cause problems.
At a minimum, it can cause the soil to compact, essentially the same as shrinking it. It can also lead to floods, if only on a small scale, which can sweep away the soil underneath your property.
This issue can often be alleviated by good planning and maintenance (e.g. be careful of planting trees near your home) but should still be noted.
The third is mining. Subsidence is a very common problem in mining areas, although the fact that this is well-known does help to put people on alert for it.
If at all possible, you want to know about subsidence issues before you buy a property
Subsidence, or the clear potential for subsidence, doesn’t need to be a complete deal-breaker for a property purchase but it does need to be factored in to any offer made.
This is one of the many reasons why it’s worth spending the money on a proper survey rather than just a basic valuation.
Minor subsidence may not be an issue but major subsidence generally needs urgent treatment
It’s perfectly normal for buildings to “settle” a bit after they are built, so you may even see brand new properties with hairline cracks in the walls. If they’re smaller than about 0.5mm then they’re unlikely to be an issue.
If, however, you see signs of major subsidence, then you need to look at urgent remedial action.
Signs of major subsidence include:
- Wide cracks, especially if they are zigzagging and visible both internally and externally
- Sloping floors
- Windows or doors not fitting in their frames properly
- Skirting boards coming away from the wall
- Puddles/pools of water with no obvious reason for their existence
The traditional treatment for subsidence was underpinning the foundations of the building. This has largely been replaced by resin polymer injections. When injected, the resin polymer expands, fills any gaps and supports the property.