what is subsidence

What Is Subsidence

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    Subsidence occurs when the ground underneath your house sinks. As the ground moves lower, the foundations of your house can become misaligned. It is particularly problematic when the ground under your property is sinking at different rates. Subsidence is not the same as heave, which is where parts of the ground under your home shift upwards pushing the foundation s higher. It is also different to a landslip or landslide, where the ground your home was built on moves down a slope or is washed away.

    It is also worth noting the difference between subsidence and settlement. According to the Financial Ombudsman Service, subsidence is caused by the 'downward movement of the site on which a building stands – where the soil beneath the building's foundations is unstable. Whereas settlement is "downward movement as a result of the soil being compressed by the weight of the building within ten years of construction". It is important to know the difference as most home insurance doesn't cover the settlement.

    One crack in a wall is not a sure sign of subsidence. It is far more likely that the crack is a result of the walls or ceilings of your home swelling and shrinking over time due to temperature changes. Also, a new home – or one that has had some major plastering – may develop some cracks as the plaster dries out or the structure settles onto its foundations.

    A crack caused by subsidence is likely to be:

    • Wider than 3mm – that's the width of a 10p coin
    • Visible on both the outside and the inside of your home
    • Diagonal and usually wider at the top than the bottom
    • Located close to a door or window

    Cracks aren't the only sign that you may have a subsidence problem. You should also look out for doors and windows that stick as this could be caused by the frames warping as part of your house sinks. Keep an eye on wallpapered rooms for signs of rippling at the wall and ceiling joints. You may also spot cracks where an extension has been joined to your main home.

    5 Warning Signs Every Homeowner Should Know

    In a nutshell, subsidence occurs when the ground underneath a property begins to collapse and takes the building's foundations with it. This causes one side of the house to sink and those suspect cracks to appear.

    Subsidence is a different issue to ground heave, which is when the ground moves upwards rather than downwards, requiring a different course of action.

    Of course, small cracks are a common sight in most properties, and not all are a cause for concern. All new builds and home extensions will shift slightly as they settle, so small hairline cracks under 0.5 millimetres in width are normal.

    However, larger cracks radiating from windows, doorways or corners can indicate that your property's foundations have begun to sink – especially if they've grown over time. 

    Ground engineering specialists Mainmark have outlined five key subsidence warning signs to watch out for:

    1. Sinking or sloping floors: this can indicate that the ground beneath your home is collapsing, and urgent attention is required.
    2. Cracks in walls, paths and driveways: take note of any cracks that form a zig-zag pattern following the mortar lines of your home's brickwork. Cracks caused by subsidence are usually wide enough to fit your little finger into and are visible internally as well as externally.
    3. Windows and doors becoming misaligned or jammed: if your home's foundations are sinking, this can cause problems with cracks around joins – sort this before they develop further.
    4. Skirting boards separating from the wall: visible gaps suggest that your home could be suffering from some serious movement issues that need remedying. 
    5. Formation of puddles around the perimeter of your home: this can indicate a problem with drainage. Pooling water can then soften the soil and destabilise the ground beneath your home – more on this below.

    What Causes Subsidence?

    There are some factors that make your home more susceptible to subsidence than others.

    The level of moisture in the ground can cause problems. Clay soil especially can shrink, crack and shift during the summer heat, wreaking all kinds of havoc on your foundations. 

    Drought-prone areas are more at risk, as the ground is drier and thus more likely to crack while having an abundance of trees or shrubs close to your home can also dry out the ground as the roots may absorb a lot of water.

    But the ground becoming too damp can also be an issue. Leaking drains can wash away or soften the soil, causing it to compress and sink under the weight of your home.

    As always, prevention is better than cure, and there are a number of steps you can take to lessen the chance of subsidence occurring.

    While everyone covets a lovely leafy garden, it's best to limit the growth of trees and large shrubs to prevent them from drying out the soil.

    Make sure any new trees are planted at a distance from your house – take note of the variety you've chosen, too, as some take in more water than others. If in doubt, go for an evergreen species that won't absorb as much water.

    It's important to stay on top of the upkeep of your home to prevent drains from flooding and the ground from becoming oversaturated. Check for blocked or leaky drains and keep gutters clear. Especially of concern during the wintertime, check pipes for splits and leaks.

    Frequently Asked Questions

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    How To Fix Subsidence

    The best course of action is to contact your insurer. They'll be able to arrange for a full survey to assess your home's structure. If subsidence is found, there are typically two options available: underpinning and resin injections.

    Concrete underpinning requires raising, re-levelling and re-supporting the building with an additional foundation layer. This can be a slow and costly process that may require you to leave the property while work is completed.

    A more modern solution is to inject a resin polymer into the ground at certain points. The material expands as it travels into the soil below, filling the gaps. In most cases, a house can be treated in a matter of hours and shouldn't require you to leave while the work takes place.

    Resin injections are usually cheaper than underpinning as it's a less labour-intensive process and takes less time to complete. However, if there is only a small section of your foundations that requires underpinning, the older method may be more cost-effective. Your surveyor will be able to advise.

    You'll then need to fix any cracks that have occurred. Minor ones that don't affect the structural integrity of your home can often just be filled in and painted over once the cause has been treated. Wider ones that affect the structure itself may require the walls to be repointed and repaired with metal fixings.

    Natural Causes Of Subsidence

    Natural causes are obvious when you take a moment to think about the process that is happening when subsidence occurs.

    Moisture plays a huge part in subsidence, and problems manifest in a number of different ways. In areas where the property is built upon cohesive soils such as clay, for example, subsidence can occur due to the nature of the soil itself. Clay, like silt and, to a much lesser extent, loam, will swell and shrink with rising and falling moisture content, causing natural shifts which could affect the big pile of bricks above that you've chosen to live in.

    Non-cohesive soils (think gravel and sand), on the other hand, are not likely to shrink and swell with changes in water content, but they are at risk of being washed away should there be a prolonged period of water flow in the area. This can be caused by extended periods of wet weather or, more commonly, by damaged water pipes (see below).

    Some soils will also break down over long timeframes, and this decomposition can slowly change ground levels and affect foundations. Homes built on mixed soils can suffer, too, as the earth responds differently in certain areas, thus shifting and moving at an uneven rate. This can cause serious problems, as the varying rate at which the soil moves can dramatically impact a property's foundations.

    Trees, shrubs, and bushes can all affect the moisture content of the soil as well, especially when there has been little to no rainfall. Plants, especially more established ones, will draw the water they need to live up through their roots, leaving the soil dryer and susceptible to shrinkage. Obviously, this doesn't mean you should remove every bit of greenery in sight, but badly planted and landscaped foliage can be a cause of subsidence. This is particularly true if you have thirsty trees nearby like beautiful willows, which are commonly found by rivers for that very reason - they need a lot of water to survive and thrive.

    Man-Made Causes Of Subsidence

    Just as natural causes of subsidence are obvious when you stop and think, so too are man-made causes. The difference is that they are infinitely more frustrating as they could have often been easily avoided with a little more care and forethought.

    Common culprits of man-made subsidence problems include poor foundation work and/or improper ground preparation when the property was built, and the reasons for these causes can vary from incompetence to penny-pinching.

    Seemingly innocuous things like traffic and nearby building work can affect the structural integrity of a property as well. One wouldn't necessarily think that innocent vibrations from cars rolling by would have such a dramatic effect, but such persistent rumblings can cause soil to move if traffic is heavy and repetitive.

    Again, water plays a big part, but from the perspective of man-made causes, poor drainage or damaged pipeworks are usually responsible. Buildings built near old mine shafts in certain parts of the country can suffer from subsidence, too. Thankfully this isn't much of an issue in Wanstead!

    How To Check For Subsidence

    Spotting the signs of subsidence early will make fixing the problem much easier, but you need to keep things in perspective and not let your mind automatically assume the worst (easier said than done, I know). The most common 'tell' will be cracks in your walls, but not all cracks are created equal!

    Many cracks will be perfectly normal and nothing at all to worry about. Almost every home in the country will have a crack somewhere or other, so it's important not to worry too much if you spot one. Natural shrinkage of plasterwork and even changes in humidity or temperature can cause cracks to appear, and, as a rule, these hairline cracks are nothing to worry about.

    Subsidence cracks, on the other hand, will look entirely different. Sure, there's every chance that a crack caused by subsidence will start off small and grow bigger with time, but there's a difference between monitoring a crack and worrying about it unnecessarily.

    Below are some of the ways you can distinguish harmless cracks from those caused by subsidence.

    How Much Does Subsidence Devalue Property?

    This is a common question posed by those affected by subsidence. Unfortunately, there's no definitive answer that will cover all circumstances, as each case will differ greatly. Numerous factors are at play here, from the extent of the damage right the way through to what part of the country you live in... there's simply no way of putting a sensible figure on how much subsidence will knock off your property's value.

    One point to bear in mind, however, is that fixing the problem yourself will generally be cheaper than offering the property to market with the issue outstanding. Should the subsidence be at an advanced stage, many lenders won't even agree to lend, so it could be your only course of action anyway.

    Do I Have To Declare Subsidence When Selling?

    This is somewhat of a grey area. While you should definitely let prospective buyers know about any major issues, you are not necessarily obliged to do so. This is obviously deceitful and not recommended, but you can effectively avoid telling a buyer about subsidence without putting yourself in a legal predicament.

    That being said, should you be asked about subsidence, or any other issues for that matter, you could be sued for misrepresentation if you do not declare it fully, and the likelihood is that you will be asked. Honesty is by far the best policy in this instance, as trying to cover it up will run the risk of landing you in court.

    Between your estate agent's Property Information Questionnaire, the buyer's conveyancing solicitors' checks, and their surveyor's surveys, it's extremely likely you will get caught out and have to face the consequences of your actions.

    So, to reiterate, the likelihood of pulling the wool over your buyer's eyes is negligible, and you should also consider the moral and (potential) legal implications of trying to do so. Do the right thing and be straight with your buyer.

    After all, it's what you'd want if the shoe were on the other foot.

    How To Reduce The Risk Of Subsidence

    When the ground under a property moves by sinking downwards, the building foundations are put under huge stress. Issues like this often become apparent within the property as cracks appear in the walls, particularly near windows and doorways.

    While subsidence can take many months or even years to become obvious, you can take steps to reduce the likelihood of being affected by subsidence.

    Remove trees and bushes planted near the house. Trees are one of the most common causes of subsidence as the roots withdraw moisture from the soil supporting the foundations.

    If you cannot remove the trees, maintain them with regular pruning. This should curb their growth and limit their search for water close to the house.

    Carry out regular inspections of your property, paying particular attention to pipework, gutters and drainage systems in case of leaks and/or blocks.

    Homes can also be affected by subsidence because of location, such as old mining towns and soil type in the area. Clay soils, in particular, are susceptible to subsidence as the soil dries and shrinks or absorbs water and expands.

    If your property has been affected by subsidence

    Measures can be taken if your house has been affected by subsidence. Early detection is key to reducing the impact on any property, and if caught in time, it will rarely result in repair works being made to the foundations.

    If you do need repairs, or you are considering purchasing a property that has been affected in the past, then you should speak to your home insurance provider. Not all providers will cover subsidence, especially if a house has been underpinned.

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