What Is Subsidence and How Do You Spot It?

What Is Subsidence?

Generally, subsidence is the name for movement in a structure that causes the building to sink or move downwards. This usually happens due to changes to the ground. There is very little or no lateral movement. This is what distinguishes it from a land slip or settlement, which occurs when the building’s weight compresses the ground from below. Instead, subsidence is an effect of the ground moving, which affects the structures above.

All three of these issues can affect properties in similar ways. So, if you suspect the buildingyou’re in is moving or has moved. Experienced professionals must assess and diagnose it. Otherwise, you could end up with the wrong kind of rectification put in place, which could even make the issue worse.

What Are The Signs of Subsidence?

Subsidence almost never effects the entirety of a building’s foundation consistently. Which means part of the foundations move differently and cause cracks in the structure above. This can cause cracks internally, externally, or both!

On the outside, these cracks will normally show up as diagonal cracking usually travelling through the mortar lines, becoming wider as the crack rises up. This type of crack usually start at a low level as well as around openings like windows and doors. Which are the weakest points in the walls. Subsidence cracks often travel through the Damp Proof Course at the bottom of the wall as well, where they’re not as easy to see.

Internally, cracking tends to turn up around the corners of windows and doors. Usually reflecting the racking on the external side.

How quickly can Subsidence appear?

In some cases, these cracks can appear slowly, or they can turn up quickly in just 24 hours. We’ve even been surveying properties where on one visit there’s no cracking, but when we visit the next day there are large cracks. The most memorable was when we were surveying during a very hot summer. On day 1 there were no cracks, but when we came back the next day the garage has developed huge cracks. We worked out that this was thanks to the clay soils drying out and shrinking in the heat. Which meant the foundations couldn’t resist the forces of gravity any longer. But there were no signs of this issue showing just one day before!

The cracking from subsidence will often start as what we refer to as hairline cracking. This is a thin but noticeable crack, and can develop into much larger cracks. Once the cracks get to about 3mm wide (or the thickness of a coin). That’s when we start to get concerned. Finding cracks of this size suggests more serious issues and should be given swift attention.

I Think I Have Subsidence, What Should I Do?

If you’ve noticed cracking in your property and are concerned, we always recommend you ask an experienced surveyor. They can help confirm the cause of the crack and identify all the clues that might be around the property that point to the right solution.

In our experience, the majority of subsidence issues we look at don’t need urgent action. I If they do, we may recommend implementing propping or other measures quickly to keep everyone safe. If you’re in doubt, always get someone to inspect and confirm subsidence suspicions. Fixing the issues early can prevent unnecessary damage and avoid expensiverepairs if the problem worsens. In most cases, we will recommend installing equipment called ‘telltales’ and keeping a regular log to record to record any further movement. If there is still movement, the speed at which the cracks are growing can be measured and appropriate repairs recommended.

What Causes Subsidence?

Unfortunately, there are a few things that can cause subsidence, which is why it’s so important to identify the cause. For example, the following factors are known to cause subsidence:

And more!

Repairing the subsidence is a waste of time and money until you identify and fix the underlying cause. Since the ground will keep moving. At Harrison Clarke, we find that the most common cause of subsidence is damage drainage, which can wash away the fines in the surrounding soils. But every case is unique.

Can The Building Be Repaired?

If the building has stopped moving and you have identified and rectified the cause of subsidence, it’s time to assess the damage. You often won’t know the true extent of the movement until you complete this step. Fixing it will then make the structure stable. In this instance, a simpler repair can be done to repair the cracks in the building. This is normally done with helical ties, which are small, twisted metal rods that are inserted into the mortar line of the masonry to reinforce the walls. The pointing between the bricks is also replaced at this stage.

Buildings affected by subsidence might also need to be underpinned. This is where the area below the foundations (assuming the building was built using a foundation) is removed in sections so that a new concrete foundation can be laud underneath. This foundation is laid down to firm the ground, reinforcing and stabilising the structure.

Modern Repair Methods:

Depending on the form of construction, some more modern methods might be used where suitable. This can include a pressurised injected expanding resin system. This method is particularly good because the expansion of the foam (which is essentially a super-strong expanding foam) can actually push parts of the building to move back into (or closer to) their original position. This is normally a more expensive option, and isn’t suitable for all buildings and situations.

Ultimately, if you suspect that you might have movement in your building, we advise you ask a surveyor to inspect and confirm the type of movement and the likely cause. Depending on what they find, the damage may be covered under your buildings insurance – but it’s important to check your policy on that. If you have any questions, or would like to know how Harrison Clarke could help, just contact our friendly team on 02381 55 00 51.

For more expert advice on surveying and property matters, check out our range of informative videos on our website or YouTube channel. Harrison Clarke Chartered Surveyors is here to guide you every step of the way!

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