What is Subsidence?

If you’ve found cracks appearing in the walls of your property, or seen them in a property you’re considering purchasing, then you’ve probably feared the worst.

Subsidence can be a major problem; it can hinder your mortgage application, increase your insurance premiums and reduce the value of your property. It’s no wonder that the mere mention of the word strikes fear into the hearts of homeowners.

But don’t panic-cracks do not necessarily mean that your house is subsiding!  And even if it is, there are things that can be done.

We’ll walk you through subsidence step by step and, if you think you may have a problem, use our checklist to find out if you need to call an expert.

Subsidence – What’s the Crack?

Subsidence is caused by movements in the earth beneath your property that cause the foundations to sink, putting stress on the structure of your building.

These movements can happen for a number of reasons:

• Certain soils are susceptible to changes in weather. Clay soil, for example, can crack and shift as it dries out during hot, dry periods;

• One of the most common causes of subsidence is tree roots that have grown too close to foundations. Tree roots are effective at removing water from the surrounding soil and can accelerate the drying and shrinking of soils;

• Leaking drains and water mains can weaken or even wash away the soil around your foundations.

Subsidence is thought to affect about 40,000 homes a year and is more prevalent in the South-East due to London clay, a type of soil that can expand and shrink greatly depending on how much moisture it contains.

Spotting the signs of Subsidence

Cracks in your walls could be a sign that there is subsidence, but fear not-most cracks are harmless and can be explained by other happenings such as dried out plaster.

You should only be worried if:

• The cracks in your walls are wider than 2mm;
• They start off wider at one end and become narrower towards the other;
• They travel diagonally across your wall;
• They appear near windows or doors;
• They are visible from both the inside and outside of your property.

Use our checklist above to see whether or not you should be worried about subsidence.

Although cracks that don’t resemble the above are probably benign, it’s a good idea to keep an eye on them and check for changes in size over time.

What to do If You’ve been Affected by Subsidence.

If you find cracks that resemble the above description, act early! Subsidence can take a couple of years to fix and acting early can limit the amount of damage caused.

You will need a structural engineer to complete a report to confirm whether or not subsidence is occurring and what is causing it.

This may involve monitoring the damage over the course of a year. If you are purchasing a house that you suspect is subsiding, it’s important to commission a structural survey.

If subsidence is confirmed there are a number of possible solutions depending on the cause:

• Tree roots are thought to be responsible for 70% of subsidence cases. Where this is the case, removing the offending trees could be a simple and cost effective solution. If removing the tree(s) isn’t an option or risks making the problem worse, simply pruning the tree so that it removes less water from the soil may help alleviate the problem.

• If leaking drains or water mains are causing the subsidence, fixing the leak can solve the problem.

• If there has been significant movement in the foundations, underpinning may be necessary. Underpinning is the process of strengthening and stabilising the foundations. This is a worst-case scenario (fewer than 10% of subsidence cases result in underpinning) and is a lengthy, costly and disruptive exercise.

Costly? That doesn’t sound good.

Don’t fret! The cost of fixing subsidence problems will, in most cases, be covered by your home insurance. If you’re unsure, give your insurance provider a call or check your policy documents-you may only be liable to pay a policy excess.

As Chartered Surveyors, HLN Engineering Ltd can liaise with your insurer on your behalf and help you with any claim you need to make.  We are also on hand to assist with the design and coordination of any work that needs to be completed in order to fix the problem.

Can Subsidence Be Prevented?

Whilst it’s not possible to prevent subsidence entirely, you can minimise the risks:

• Make sure trees are planted a safe distance from your property;
• Prune existing trees and other foliage to regulate the amount of water they remove from the soil;
• Make sure that drains, guttering and pipework are well maintained to avoid leaks.

HLN’s Subsidence Checklist

Concerned that your property or a property that you’re considering purchasing may be suffering from subsidence? Use our checklist from earlier to determine whether or not you need to call an expert – if you can identify two or more of the tell-tale signs, then getting a professional to check is always a good idea.

Our in-house consulting engineers are on call to assist with any subsidence issues you may be facing. 

If you suspect your house or a house you would like to buy has been affected by subsidence, call HLN Engineering Ltd on 020 8099 6388 or email mail@hlngroup.co.uk

Information on our regional offices can be found on our contact page.