What causes house subsidence?

Subsidence is when the structure of your building moves and breaks apart.

Signs of subsidence are most commonly observed in brick walls with large cracks appearing and getting further apart the further up the wall you go. The damage caused by subsidence cracks can vary massively; from tiny fractures in the wall to several foot gaps or even more.

Subsidence is generally caused by contracting clay soil, water leaks and tree roots sucking moisture out of the soil. This causes the ground to move underneath the property and tear the walls apart.

Officially, the Financial Ombudsman defines subsidence as: "the downward movement of the site on which a building stands - where the movement is unconnected with the weight of the building". Essentially, it means that the soil beneath the building's foundations is unstable.

What is ground heave?

This is commonly linked with subsidence as the damage to a property looks very similar: cracks that increase in size the higher in the building you go start to appear in the walls.

However, rather than being caused by the ground moving and tearing the wall apart, ground heave is more commonly caused by an upwards force.

Typically it's caused by dead trees near the property - large trees with extensive roots post a particular risk. This is because the tree stops sucking moisture out of the soil when it dies, so water collects and creates an upward force in a single point under a wall or structure, eventually causing it to break.

Extreme cold can also cause ground heave as the water in the ground freezes - this is known as frost heave.

What is landslip?

This is a very dramatic and obvious case of subsidence, when a whole section of the property drops several feet or more because the land has moved.

Landslip is most often found at coastal properties on cliff edges, although it can occur with mud slides and as a result of flooding as well.

Is your home at risk of subsidence?

The risk of subsidence on your property is dependent on the area in which you live, the soil conditions, nearby trees and other factors such as the depth of the foundations on which your property is built.

Put simply, if your property is on clay soil and close to large trees that need a lot of water, then you are more at risk.

However, with roughly half of UK homes built on ground that's classed as clay - mostly to the east and south and including London - that is a lot of potential exposure.

Landmark Information Group suggests that one in five properties are at risk of subsidence in the UK.

How to protect against subsidence

Make sure you control large trees around your home. Prune and crown them as trees are believed to be the cause of 60% of all subsidence claims as they take moisture out of the surrounding soil.

Check for leaking mains water and drains, as well as taking extra care when putting in extensions and other ground works that might change the support underneath your house.

Can subsidence and ground heave be fixed?

There are remedies for subsidence and ground heave but unless it is a very minor case, they all tend to be quite expensive and involve building contractors.

Underpinning is a method of increasing foundation depth or repairing faulty foundations and this is used as a remedy in more severe cases.

There are various ways it can be used: Mass Pouring (concrete into gaps under the foundations), Screw Piles and Brackets (tension and compression on existing walls when mass pouring cannot be used), Pile and Beam (when there is restricted access) and Piled Raft (when the whole structure needs support).

Can insurance protect you from subsidence problems?

Yes. Most standard home insurance policies will offer some subsidence insurance cover but most will set a high excess (around 1000+) on claims because it's an expensive problem to fix.

Check your own policy for exact wording and if subsidence is omitted, then change insurance policy quickly.

Bear in mind that the subsidence component will usually only be extended to properties without a prior history of subsidence, if you've made a claim then you'll need to get specialist protection.

Once you have claimed for subsidence you become more risky in the eyes of insurers. However, you will still need to declare the claim when you apply for a new policy.

It really isn't worth omitting this detail because if you are found out by an investigator - which invariably will happen if you make another claim - then your insurance could be refused and you will end up paying for the claim yourself. Furthermore, the rest of your insurance will be invalidated and your insurer may even accuse you of fraud.

When you declare a claim for subsidence tell the insurer of any remedies taken and any claim free time since.

The best thing to do is to speak with specialist subsidence insurers as they understand the problems, fixes and risks moving forward. It is their business to make a competitive quote possible as they make their living from this speciality.

What will subsidence insurance cost?

The cost of subsidence insurance will depend on the severity of your prior claims and the remedial work that has been put in place.

Generally if you have guaranteed fixes in place then this can be taken into account by the specialist insurer who will give a realistic quote on the property.

Excess can be high or low depending on the risk profile of the property.

The best thing you can do is to make as robust a solution as possible if you have a claim: make sure the work is carried out by approved contractors, where possible get warranty on the work and remove trees that could cause future problems.

Get quotes from at least two or three specialist subsidence insurers and have them compete for your business. This is a competitive market place and you will see differences in price.

And remember, the lowest price may not be the best policy, make sure you are covered for subsidence moving forward and that you have an affordable excess if you need to make a claim.