Subsidence: how to spot it and how to solve it

Subsidence, the word every homeowner dreads to hear — but it need not spell disaster. Our guide covers everything, from causes to what it may cost to rectify

run down house
(Image credit: getty images)

Although a subsidence is certainly not something you want to find in your property, it is surprisingly common and doesn’t always mean you can’t get home insurance, cause irreparable damage, entail a huge amount of disruption or result in crippling financial outlay. 

It is also worth noting that cracks and movement in a house are often misdiagnosed as subsidence when there is actually something else that has caused them. In fact, a great many insurance claims for subsidence turn out to simply be cosmetic damage, caused by movement after an extension or alteration for example. 

Our guide to subsidence will explain everything you need to know to ensure that, should you find yourself dealing with this issue, you are fully equipped with all the knowledge required. 

What is subsidence?

Subsidence in houses is when the ground underneath the building sinks — or subsides. Due to the ground moving, the foundations move and, as the ground sinks and moves, cracks appear and the stability of the building is compromised.

It is important not to confuse subsidence with heave or settlements. Heave occurs when the ground beneath the house moves upwards, and settlement happens when the earth beneath becomes compressed under the weight of the house, causing the whole thing to shift downwards — this usually happens within 10 years of a property being built. It can be extremely difficult to get house insurance on a house with settlement.

Subsidence is also different from a landslide as this is when the ground moves down a slope or becomes washed away.  

What causes subsidence?

There are several causes of subsidence. Sometimes, the ground under a section of the foundations will shrink meaning there is no support for the wall above that part. Common culprits include large tree roots sapping moisture from the ground, particularly in periods of drought. It has been estimated that around 70% of subsidence cases are caused by tree roots. 

Another common cause is soil type — clay is particularly prone to shrinking, cracking and moving in long dry periods.

Leaking drains or water mains can also lead to subsidence, weakening the soil so that it sinks.

Shallow foundations can also be a contributing factor — older properties were often built with shallow foundations although their construction of masonry and lime mortar often deals well with movement. 

Finally, homes built close to old quarries or in mining areas can suffer from subsidence — subsidence claims reports are available from the local authority.

Whatever has caused the subsidence though, the most important thing to ascertain, and certainly the thing that will affect your ability to get home insurance, will be whether the movement is ‘historic’ or ‘progressive’ — meaning has the subsidence now stopped or is it still likely to cause further damage?

Signs of subsidence

Cracks are not always a sign of subsidence. However, certain types of crack can point towards trouble. These include cracks that are: 

  • Wider than 3mm
  • Running diagonally
  • Wider at the top than the bottom
  • Visible internally and externally
  • Near doors or windows

Other signs of subsidence can include:

  • Doors or windows that stick in their frames
  • Wallpaper that has rippled at the joints
  • Very uneven floors

How is subsidence fixed?

Depending on the cause of subsidence, it might be quite easy to stop it in its tracks and, contrary to popular belief, underpinning is not always necessary. 

If it is discovered that the subsidence is being caused by tree roots nearby, the tree can be removed — something that should only be done in consultation with a surveyor and a tree surgeon. 

If leaks in pipework have been identified as the cause these should be fixed before checking that the property has stabilised. 

Underpinning should only be undertaken as a final resort — it is expensive and disruptive and often unnecessary. In fact, according to the Royal Institution of Chartered Surveyors (RICS) fewer than 10% of properties with subsidence need to be underpinned.

How much does it cost to fix subsidence?

This depends on the cause, but, according to data from the Association of British Insurers, the average payout for subsidence is £6,250. However, should underpinning be required, costs can run to tens of thousands, although a more typical cost for underpinning the average house would be around £10,000 to £15,000. 

Subsidence and house insurance

It is still possible to get home insurance on a house that has suffered from subsidence, although most insurance companies will want to monitor and measure the movement over at least 12 months in order to try to predict the risk of future movement. 

Most house insurance policies do cover subsidence but only when a house has not suffered from it in the past. Look for policies that cover repairs to damage caused by subsidence, alternative accommodation and lost or damaged items. 

Houses that might be particularly prone to subsidence, such as those in coastal areas, can benefit from specialist insurance.