Subsidence, meaning the sinking of land, can be extremely serious for homeowners, and potentially expensive to remedy. If the ground under a building becomes unstable, the structure is likely to be affected. Damage may range from relatively minor cracks in walls to severe damage which may make the dwelling a dangerous liability. Let’s take a professional look at common signs of subsidence and the causes.
The first sign of subsidence problems is likely to be cracks appearing in exterior or interior walls. On the outside of a building, subsidence cracks most frequently zigzag along the lines of mortar between bricks. Particular areas of vulnerability are where extensions join an older part of the building. In all cases, the wider the cracks, the more likely it is that there is a serious issue.
Inside the building, signs of subsidence will be cracks in plasterwork or exposed brickwork. Other worrying indicators can be windows and doors getting stuck, and wallpaper wrinkling. If there is reason to be concerned, it is time to find a RICS qualified surveyor for a professional opinion, and to find out about possible solutions.
What is the difference between settlement and subsidence?
Any new building is subject to settlement as the ground compacts under the weight of the structure. The results are most likely to be minor cracks in internal walls which can be easily filled. Settlement is part and parcel of buying a newly built home and is not a cause for concern.
Cracking in new builds can also be the result of materials such as mortar and plaster shrinking as they dry out. After one or possibly two years, any settlement or cracking issues will be over. If problems persist, there is a risk that the ground preparation work was not properly performed, and there could be a risk of subsidence and the need for further investigation.
What are the causes of land subsidence?
Subsidence occurs for a variety of natural and man-made reasons. The most frequent natural causes are tree roots and weather conditions. People on the other hand are responsible for substandard construction work and historic causes such as collapsed mines.
How do trees cause subsidence?
It is never a good idea to plant trees close to buildings, especially trees with long roots such as sycamores, oaks, ash, willows, and poplars. Roots under a building will draw off moisture and keep growing. The result can be damage to foundations and drains, as well as weakening the ground structure.
Does the weather contribute to subsidence?
In prolonged periods of dry weather, soils, especially clay soils, are prone to shrinkage. As a result, the ground support for foundations is weakened, with the result of potential damage to the structure. Too much wet weather can wash away loose soils such as sand and gravel with the same result.
Which building defects can cause subsidence?
One of the disciplines of responsible construction is to ensure that the ground is suitable for a new building. Current planning policies are designed to make sure that building land is in the right condition. If not, regulations require that degraded or unstable land be made good. Where current standards have not been applied, including for older buildings, it is possible that the ground has not been properly compacted or wrongly prepared.
There are also strict requirements for foundations, covering depth, width, materials and any enhanced support. If the regulations have not been followed, the integrity of the structure may well be compromised.
Homeowners also need to be aware of potential damage to the ground from leaking gutters and drains. Excess water from either source can cause problems in the same way as prolonged rainfall.
Other factors which can cause subsidence
Where a building is over or close to old mines and quarries, there is a risk of land sinking into the cavities below, with potentially serious consequences. Extensive regulations apply to risks from historic works, so homebuyers are, in theory, well protected.
There are further possible problems for structures close to very busy roads. Vibrations from heavy traffic can result in ground movement, as can construction using heavy equipment on neighbouring land.
Potential further issues are landslips and erosion, especially for buildings on vulnerable, high ground in coastal areas. Landslips in areas by the sea in Hampshire, Dorset and Devon are testimony to the way that erosion can radically alter the landscape and make buildings unsafe or even destroy them.
When a subsidence survey is required, it needs to be carried out by a RICS-qualified Chartered Surveyor. At Robinson Elliott, our buildings defect reports provide a detailed assessment of the site environment and land conditions. As a result, clients have a clear view of the risks, and any evidence that the property has already been damaged.
For buyers, this adds a level of confidence about decisions of whether or not to proceed with a purchase. For homeowners, our surveys and reports give clarity on the extent of any subsidence and the risks for the future. Since subsidence issues can have a significant bearing on house values, sellers need to be armed with a full picture before putting their homes on the market.
Our building defects reports include advice on further investigation and on repairing any significant defects. The reports are important for buildings insurance purposes, and help to ascertain the correct amount of cover buyers and owners require.
Subsidence problems can frequently be solved by carrying out appropriate work to reinforce a building’s foundations. Tree roots account for a very large proportion of the damage caused by subsidence. By removing any tree or shrub close to the property and controlling the roots, all may be well. Cracks can be filled to repair walls and structures, but the building needs to be closely monitored to ensure that there is no further evidence of subsidence.
A CCTV drain survey can reveal if broken drains are the problem, and if so drain repair and replacement may well be the solution. Leaky gutters are simpler to make good, but it is essential that the work is done as soon as the problem is identified.
If none of the above causes of subsidence can be identified, the next step is to consider underpinning to strengthen the foundations. Underpinning is specialist work, and homeowners should take advice from qualified surveyors such as the Robinson Elliott team. In addition to giving you a clear idea of the defect, we can put you in touch with trusted professionals who can carry out the work.
Next steps for homes with subsidence
Once you have a full surveyor’s report on how subsidence affects your property, you can make informed decisions about continuing to live in your home, or putting it on the market. As long as it is safe, there is no reason to put a brake on your plans, but it is advisable to get remedial work underway as soon as possible. In the case of extensive underpinning, it may be best to move out while the work is carried out, but it is by means always necessary to do so.
To find out more about how we can help with subsidence issues, please do get in touch. Our experts are on hand to offer advice and assistance, and will be happy to answer any questions you may have.