What is subsidence? 5 warning signs every homeowner should know


Updated on 25 October 2019 | 0 Comments

Any crack in an internal wall may well have you asking what is subsidence? With thousands of homes affected every year, it can reduce your property's resale value by as much as 20%. Here's how to spot it and stop it in its tracks...

A problem that plagues many properties in the UK, subsidence requires urgent and immediate attention.

Affecting more than just the structural stability of your home, those tell-tale cracks can cost your home up to 20% of its value if left to linger, so it’s important to be able to spot the signs and effectively treat the root cause before it wreaks real havoc.

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Often built with shallower foundations, old homes can be especially at risk, however, you shouldn't underestimate the threat posed to newer properties too.

What is subsidence?

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.

5 subsidence warning signsMany cracks found in homes are harmless. Image: Kwangmoozaa / Shutterstock

Of course, small cracks are a common sight in most properties and not all are a cause for concern. All new builds and 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. 

How to spot subsidence

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.

5 subsidence warning signsA dropped floor level can be a cause for concern. Image: iamskyline / Shutterstock

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.

5 subsidence warning signsKeep an eye out for diagonal cracks. Image: eelnosiva / Shutterstock

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.

5 subsidence warning signsSubsidence can be common in older properties. Image: Barnes Ian / Shutterstock

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 subsidence warning signsMonitor your skirting boards for movement. Image: billh18 / Flickr

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.

5 subsidence warning signs Standing water near your home could spell trouble. Image: VDB Photos / Shutterstock

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.

Preventing subsidence

As always, prevention is better than cure and there are a number 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.

8 subsidence warning signsIt's important to keep drains and gutters clear. Image: Suzanne Tucker / Shutterstock

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.

5 subsidence warning signsTraditional underpinning can be an extensive process. Image: s74 / Shutterstock

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 require 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 re-pointed and repaired with metal fixings.

READ MORE: 10 warning signs that you're looking at a money pit

Featured image: eelnosiva / Shutterstock

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