What causes subsidence and how can I easily fix it?
- By: Ashley Saunders
- December 2019
Nothing scares a potential homebuyer like subsidence! But, what is it? Are there any telltale signs? What causes subsidence? Can you fix it?
While you’ve probably heard the term subsidence, unless you’ve been unfortunate enough to live in a property with it, you might have little idea of what it actually is.
Thankfully subsidence is usually easy to spot. We’ll help you decide whether you should walk away from a property you’re looking at buying or if the issue can be fixed.
What causes subsidence?
At its most basic level, it’s when a house sinks into the ground, taking some of the building’s foundations with it. Cracks appear as one part of your property’s structure is under more strain.
The type of soil has a massive impact on the likelihood of subsidence. For example, homes built on clay are more likely to suffer from subsidence than properties built on other types of soil.
The weather also has an impact on the severity. After a heavy downpour, the ground expands as moisture seeps into the soil. While after some hotter weather, the ground contracts as some of the moisture evaporates.
So, while we all might long for hot summers, such weather can be bad for homes built on clay.
Is it different to heave or landslip?
Heave is the opposite of subsidence as the ground is pushed upwards, forcing part of the foundation up with it.
Landslip or landslide is where the land travels down a slope or is washed away. As a result, part of the property or foundation moves with it.
What are common causes?
Explaining what causes subsidence is quite simple. The basic concept centres around the expansion and contraction of soil, there are several situations which could cause your home to subside.
In addition to heavy rain followed by hotter weather, common causes also include leaking drains and tree roots.
An overflowing or leaking drain can increase the amount of moisture in the soil, and therefore create the conditions for your foundations to move. So it’s worth keeping your drains clear of debris and in good shape.
Depending on the tree, roots can spread in all directions for metres as they search for moisture. So while it appears beautiful, the tree could be the cause of many issues. Larger trees like Willows and Elms are among those well known to cause subsidence if planted too close to your home.
Another common cause is former land use. For example, living near or on top of a former mine can result in unstable foundations. In the worse cases this can lead to structural damage. You can easily check if you’re in an affected area by using the Coal Authority website.
Some older homes have shallower foundations, which increase the risk of subsiding. However, as they were built using soft lime mortar and bricks, they can be more flexible and less likely to be badly damaged by any movement.
How can I tell if my house subsiding?
It can be quite hard to spot early signs as your home is unlikely to start drastically sinking into the ground! So you need to be on the lookout for distinctive cracks in your walls.
These are different from cracks that appeared when the house was settling and are quite distinctive. Cracks from subsidence can:
- Appear and spread rapidly compared to regular cracks
- Thicker than a 10p coin (more than 3mm)
- Visible both inside and outside
- Look narrower at one end than the other
- Run diagonally across the wall
- Found close doors and windows
Other telltale signs include:
- Doors and windows start to jam as they’re out of alignment or frame has warped
- Wallpaper crinkling at the wall/ceiling joins
- Cracks where any extension joins the property
Reducing the risk
While you can’t control the weather, you can ensure where trees and shrubs are located in relation to your property. You’ll want to plant them at least 6 metes from your property.
If you already have mature trees or shrubs, don’t worry or reach for the nearest saw! Instead, ensure they’re carefully managed and regularly pruned. You may want to speak to a tree surgeon, especially if you have large trees near your property.
If you’re unsure about safe planting distances, then check with the Association of British Insurers (ABI) as they have a wealth of information on their website.
While you’re outside pruning your shrubs and trees, it’s worth taking some time to check and clear your drains and guttering. Any blockages could cause a rise in the soil’s moisture content, making subsidence more likely.
Even if you live in an area with little annual rainfall, it’s worth investing in a DIY rainwater harvesting system. Such a system will capture rainwater which can be reused within the home and lessen the amount of moisture which reaches the soil.
It’s worth checking and monitoring any cracks, especially those who suddenly appear and rapidly grow. And remember cracks can form both inside and outside, so it’s always worth having a good look.
I think my home is subsiding, what can I do?
The first thing if you spot signs of subsidence is to not panic as there’s usually a straight forward solution. By it’s worth spending some to figure out what causes subsidence in your case.
Your first port of call should be to check whether your home insurance policy covers subsidence. If it does then your insurer will be able to advise on the possible solutions and the next step.
In some cases, you’ll need to engage a surveyor, who will monitor your home over a few months. This is preferred to taking invasive action, although they might decide to drill a hole into the ground.
More obvious damage to the foundations may need to be investigated and soil samples may be taken.
With minor cracks which don’t affect the structural integrity of your home, you can often fill them and paint over as long as the cause is removed.
Anything more serious that might have an impact on the structure may result in walls needing to be re-pointed and repaired with metal fixings.
Your home may need to be underpinned. This is where an additional solid foundation is laid below ground level to add strength.
In some rare cases where the cracks are deemed to be severe, major reconstruction and some rebuild may need to take place. You may need to hire a structural engineer to ensure the work completely remedies the issue.
Will I be covered by my home insurance policy?
It’s impossible to say as the kind and type of coverage varies between insurers and policies. So it’s critical to check any terms and conditions before accepting a policy.
Another element to be aware of is your subsidence excess as many insurers apply a higher amount for any damage caused by subsidence. Usually, the excess is £1,000, but this amount can vary massively depending on whether your home has been previously affected.
When taking out a new policy, it’s best, to be honest as any claim could be rejected if you don’t, for example, declare the home is already subsiding or has previously.
Putting subsidence into perspective
What causes subsidence in the majority of cases is clay soil. But before you panic, put your house on market and start testing every patch of mud you come across, it’s worth talking perspective.
London and the South East, are the main affected areas by a larger clay content in the soil. However, only 1 in 50 houses has suffered subsidence problems over the last 30 years.