Subsidence – what you need to know to ensure you are on safe ground
Cracking in the walls of your property can ring alarm bells, indicating subsidence and all that entails – costly structural work, expensive insurance and issues when you come to sell. Although rare, subsidence can be potentially devastating for any property owner, so an awareness of the tell-tale signs and a willingness to take preventative measures if necessary is crucial for landlords to ensure subsidence safety.
But what is subsidence? How can you tell if you have it? And is there anything you can do to help prevent it?
The difference between subsidence and settlement
Fortunately not all cracks spell a subsidence issue; a frequent and far less serious cause is settlement. While confusion often arises between subsidence and settlement, it is actually fairly straightforward to understand the difference between the two.
Subsidence refers to the downward movement of the building’s foundations that is not caused by the weight of the building but rather by movement of the soil beneath the building’s foundations. Settlement meanwhile is the downward movement of the site on which the building stands, due to the ground compacting beneath the building as the ground adjusts to accommodate the increased load.
Settlement usually occurs in relatively new buildings but older buildings too will develop thin cracks due to changing temperatures and moisture levels as the walls expand and contract. Usually these cracks are harmless. However, cracks that increase gradually over a period of time are a cause for concern and should be investigated. Any cracks over 15mm require action to be taken sooner rather than later to identify the cause.
A crack caused by subsidence is likely to fulfil some of the following criteria:
- It is a diagonal crack that is wider at the top than it is at the bottom.
- It is a crack thicker than the edge of a 10p coin (3mm).
- Cracks are visible both internally and externally.
- Cracks are found close to doors or windows, or where an extension joins the house.
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Common subsidence scenarios
Hamilton Fraser’s Total Landlord Insurance team has identified a number of scenarios that account for most cases of subsidence:
Shrinkage of clay soils is the most prevalent cause of subsidence – soils with a high clay content can become dried out and shrink as a result of drought or nearby vegetation soaking up the water, causing a reduction in the amount of soil beneath a property and a shift in the foundations.
Tree roots can also cause clay shrinkage, as vegetation growing close to a building removes moisture from the soil.
Conversely, heave can cause upward movement of the ground supporting the building. Usually caused by the removal of trees, heave occurs when the moisture previously absorbed by the tree stays in the ground, causing it to swell.
In a recent claims case a property suffered subsidence due to a collapsed drain on the premises which required drainage repairs and reinstatement works. The escape of water from the collapsed drain also caused localised erosion as the finer particles of non-cohesive soil were washed away underneath the property, resulting in movement to the foundations and extensive cracks.
The claims team at Total Landlord Insurance points out that structural cracks can also occur as a result of movement to the property for reasons that are not classified as subsidence. For example:
- Lateral movement results in a bulge to the mid-section of a wall and is caused by a lack of lateral restraint.
- The construction of a property on made up ground can result in a greater risk of settlement due to low bearing capacity.
- This occurs where ground levels have been altered by infilling with soil excavated from elsewhere or from waste materials. Areas of made up ground are often used for buildings as towns and cities expand, but because of the varied nature of materials used and the uncertainty of bearing capacity, conventional foundations may be unsatisfactory.
Ensuring the structural safety of your rental property should be your number one priority as a landlord to ensure subsidence safety. Subsidence is difficult to predict and costly to fix, but there are steps that you can take to minimise the risk of and damage caused by subsidence.
- Make sure that trees and shrubs are planted at least 5-10 metres from your house.
- Regularly prune the branches on your trees and remove any that are too close.
- Keep pipes and drainage systems well maintained, to prevent water leaking into the soil beneath your house.
- Check the surveyor’s report for signs of subsidence before buying any new house.
For more information check out our guide: How to minimise the risk of subsidence. If you are worried about subsidence or any of the other issues raised call our claims team on 0345 310 6370.
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