Exeter structural engineers offer advice on subsidence, what it is, how to spot it and how to fix it.
Subsidence is where the ground around the foundations of a property moves. This can cause structural damage to the building. Subsidence can be very expensive to fix, so it is always best to get expert advice before you agree for a lot of expensive work to be carried out.
Subsidence can be caused by several factors, but the most common are:
- Mining activity has been carried out in the past near or under the property. This will collapse eventually as the shaft props are not maintained, this causes a corresponding volume of earth of shift. This is an issue in certain parts of the country, and it is always worth checking with a qualified surveyor about how to check on this. This isn't a problem in Exeter, but other man-made voids in the ground can collapse and cause a problem.
- With clay rich soils, sometimes the water table can drop, especially during to a long period of dry weather. It can also be traced back to tree root drawing water from the soil. This lack of moisture in the soil causes it to shift, settle, swell or contract. As the soil moves it pulls at the foundations causing structural damage to buildings. Different clays are affected by water at different rates.
- Water can wash the soil away. This is occasionally a issue with particularly heavy or repeated floods. It is, however, more often caused by a leaking drainpipe or water supply pipe. Even if the rate of flow is quite low it can go undetected for a long time and move a surprisingly large amount of soil. This then causes the remaining soil to move into the vacated space.
- Tectonic movement, also know as earthquakes. However we are fortunate enough in the UK not to be close enough to a fault line for this to be an issue.
Underpinning involves digging around the foundations and supporting it with additional concrete. This will usually prevent any further movement as the property will be more fully supported. Underpinning can be a lengthy, costly and disruptive procedure. Bear in mind that depending on the size and layout of your property it can cost anywhere upward of £5,000 to carry out a proper underpinning.
As an estimate, only around a quarter of all properties which suffer from some form of subsidence actually need underpinning. The Institution of Structural Engineers recommend underpinning only as a last resort. As professional members of IStructE, Jon Oates can advise you on the correct means of protecting your home or business from further damage if you are affected by subsidence.
Always remember: if subsidence affects your property, it is best diagnosed early. Also, don't panic, subsidence can usually be rectified and needn't cost the Earth.