Subsidence affects around 40,000 UK homes every year. Here’s how to spot the problem, identify its cause and stop that sinking feeling
If you have moved into a recently-completed new-build block of flats and cracks appear in the plasterwork, don’t worry. The majority of new residential buildings show signs of settlement, says Battersea estate agent Eden Harper.
Even if you live in an older building and cracks appear in the summer months, but close up again in the winter, the likely explanation is settlement, particularly if it is built from a more flexible materials than brick.
Summer cracks, as they are known in the building trade, are usually completely harmless. But it is wise to get them checked out by a qualified surveyor.
Subsidence, on the other hand, is a more serious matter. It affects about 40,000 homes every year, particularly in London and south-east England because this part of the UK has a large amount of clay soil.
A number of tell-tale signs can usually indicate if your property is sinking. These include…
A New or expanding cracks in plasterwork or the exterior brickwork
B Doors or windows sticking for no particular reason due to the brickwork shifting at a different rate to the timber or UPVC window and doorframes
C Rips appearing in wallpaper that isn’t down to a damp problem
2 common causes of subsidence
1 Soil type
If a property is built on clay soil, the moisture level of the earth is normally maintained below ground. However, if trees or bushes are planted nearby these can remove water from the subsoil so that the clay to contract, causing the foundations to sink.
Denhan Guaranteed Rent reports that about 70% of homeowners who experience subsidence issues discover that the problem is down to tree roots sucking moisture out of the soil.
But beware that removing the offending tree may not solve the subsidence issue. In fact, it could make it worse. Specialist advice should be sought from a chartered surveyor who will be able to assess whether or not a tree should be removed or just pruned in order to reduce the amount of moisture it extracts from the soil.
Even if the area is free from trees or plants, if the water table drops due to a long, dry spell or water is sucked out of the soil, the earth can again contract and cause structural damage to buildings, says M&M Property.
2 Faulty pipework
Collapsing drains, culverts and, in rare cases, hidden mine shafts can also remove the integrity of the supporting ground. The presence of buried organic material, which then rots or breaks down, can also destabilise all or part of a foundation.
If water leaks into soil with a high sand or gravel content, however, it can cause the foundations of a building to be washed away and the structure to become destabilised.
The good news is if this is the case, the problem can be rectified by repairing the leaking drain or other source of water, rather than underpinning the property.
The expensive way to cure subsidence
If underpinning is required, however, this will involve holes that are 1 metre long and around 1.5 metres deep being dug every 2 metres along the affected section or wall.
Reinforcement bars will then need to be inserted at 90 degrees into the side walls of these holes to create a homogenous foundation before they are filled in with concrete.
The intervening sections will then need to be dug out to a similar depth and filled with concrete.