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  • spotting-the-signs-of-subsidence

    Spotting the signs of subsidence

    20 March 2018
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  • Subsidence is one of the most serious problems a property can suffer, potentially affecting not only your home’s structural safety, but also its resale value.

    If you think you’ve spotted the signs of subsidence in (or outside) your home, don’t worry. Spotting the signs early gives you the chance to take positive action and prevent the damage from progressing any further. Even in the worst-case scenarios, there are ways to treat it, and then take precautionary measures for the future.


    What Is Subsidence?

    Subsidence is a very specific issue that occurs when the ground under your house collapses, or sinks lower, taking some of the building’s foundations with it. This puts strain on your home’s structure as one side sinks, causing cracks to appear.

    It’s a different problem to heave, which is when the ground moves upward and forces some of the foundation up with it, and landslip/landslide, which is when land moves down a slope or is washed away, and takes part of the property or foundation with it.


    The Risk Factors

    Not all homes are at equal risk. There are also a number of geological, man-made and seasonal variations that can make your home more or less likely to experience subsidence.

    • Clay soil can shrink, crack and shift during hot, dry weather, making the ground unstable and potentially causing foundations to sink.
    • Drought prone areas are particularly at risk because the soil is much more likely to dry out.
    • Trees and shrubs can also be a factor, particularly if they’re close to your foundations. Some species absorb a lot more water, making the soil much drier. 
    • Old homes may have shallower foundations – although if they’re built of bricks and soft lime mortar, they might also be more flexible, and less likely to be badly damaged by any movement.
    • Local mining activity is another major risk factor. Similarly, former quarry or pit sites can cause instability as fill material decomposes. Use the Coal Authority website to find out if you’re in an affected area.
    • Leaking drains and water mains can wash away or soften soil, causing it to compact under the weight of your home.

    The Risk Factors


    Tell-tale Signs Of Subsidence

    It’s important to examine each sign you spot in detail before assuming the worst. Cracks often lead homeowners to suspect subsidence. However, they’re much more likely to be caused by natural shrinkage and swelling as temperature and humidity change. New or freshly plastered homes usually develop small cracks as plaster dries and the structure settles.

    If a crack is caused by subsidence, it will be:

    • Thicker than a 10p coin (more than 3mm)
    • Diagonal, and wider at the top than the bottom
    • Visible internally and externally
    • Found close to doors and windows

    It may also extend below the damp-proof course (a layer of waterproof material in the wall of a building near the ground, used to prevent rising damp).

    Other signs of subsidence include:

    • Wallpaper crinkling at wall/ceiling joins
    • Doors and windows sticking as frames warp
    • Cracks where an extension joins the house

    Tell-tale Signs Of Subsidence


    Preventing Subsidence

    If you think your property is at risk of subsidence, the first thing to do is cut down the risks as much as possible. For example:

    • Don’t plant trees or shrubs too close to your house. The Association of British Insurers (ABI) has a handy table showing how far away different tree types should be.
    • If the offending foliage is already there, don’t dig it up. This can cause water logging or instability. Regular pruning can help reduce how much water trees and shrubs absorb, but if you’re unsure or want to take further action, ask a tree surgeon for advice.
    • Make sure that external guttering, pipes and plumbing are well maintained to avoid leaks.
    • Catch rainwater in barrels or butts and use this to water the garden.  

    Preventing Subsidence


    Fixing Subsidence

    If you think your house is subsiding, contact your insurer as soon as possible. They’ll arrange for a full survey to confirm whether or not it’s a genuine case of subsidence. With buildings insurance from AXA, you're covered against subsidence and ground heave, although there are number of exclusions – for example, if the subsidence is a result of construction or demolition, or due to defective materials or faulty workmanship. For more details, take a look at your policy wording.  

    In some cases, the problem may be monitored; which involves digging a hole beside your home to find out what’s causing the problem, and tracking how far and fast the property is moving. This can take around a year. In most cases, this will end with finding and removing the cause of the subsidence. However, in serious cases, your home may need structural support from a process called underpinning while the foundations are strengthened.