If your home is subsiding, it is basically sinking into the ground, usually due to soil shrinkage. Properties built on clay soils are particularly vulnerable to subsidence because the soils are more likely to shrink when they are dry. So, a long hot summer with no rain is potentially worrying.
Trees and shrubs can also suck moisture from the soil, especially during long spells of dry weather. Leaking drains are another cause of subsidence: if water escapes from a damaged drain it can wash away the ground beneath the foundations of a home.
What is subsidence?
Subsidence occurs when the ground beneath your home starts to sink, causing the property to move on its foundations. Clay soil is particularly prone to subsidence because it is sensitive to moisture, expanding when it's wet and contracting when it's dry.
Ideally, the ground shrinks in the dry summer months when there is little rain and expands in the winter as it soaks up moisture - so there is no permanent movement and no lasting damage. But if we experience unusually dry weather for a sustained period, clay soil does not get chance to recover and problems can arise.
Subsidence can also take place when water leaks from damaged drains below the ground, weakening the soil structure and compromising the structure's foundations.
Trees and shrubbery can have a big impact on the soil near your home as they need a lot of moisture to survive. When there isn't much rain, a tree will send its roots in search of water and can suck the ground dry up to a depth of about 6 metres and a diameter of even further. So it's perhaps not surprising that research has shown that trees are often at least partly to blame for subsidence problems - and the main culprits are ash, oak, plane, poplar, sycamore and willow.
This is why, when you apply for subsidence insurance, you might be asked about the number and type of trees close to your house - and their distance away.
So how do you tell if you property is suffering from subsidence? Cracks caused by subsidence are distinctive. They will occur both inside and outside the home, be narrower at one end than the other and may extend below the damp proof course. Subsidence can also cause doors and windows to stick as the property shifts out of alignment.
Cracks are also likely to worsen over a relatively short period of time - months, or even weeks. A 'normal' settling crack might remain the same for years.
Reduce the risk
You can help to avoid subsidence by planting any trees or shrubs a good distance from your home or any outbuildings. If there are already trees close to your property, they should be removed if they were planted after the house was built. Trees that are older than the property, should not be chopped down but should instead be carefully managed. It's always a good idea to call in the help of an expert such as a tree surgeon as tree removal and management is a specialist business.
If you are worried about a neighbor's tree, try to discuss the situation calmly and amicably to see if you can work out an appropriate course of action. And remember that some trees carry preservation orders or belong to the local authority, which means you would not be able to remove them without prior consent.
Contact your home insurance provider
Your buildings insurance should cover any damage to your property caused by subsidence, so you should contact your buildings insurer straight away if you notice cracks in your home that carry the tell-tale signs of subsidence (best to check with them if you're unsure).
The insurer will normally arrange for a structural engineer to come round to assess the problem. It might be necessary to monitor the cracks over a period of time, often at least 12 months.
It is rare that a property will require underpinning - a fairly drastic solution when subsidence strikes - but you might need to move out of your home while repairs are carried out. If so, the policy should pay for suitable alternative accommodation.
Subsidence insurance claims can be expensive, so the policyholder will usually have to pay a high excess. Check the details of your policy but it could be as much as £1,000 or even £5,000 in high-risk areas. It's also worth bearing in mind that most policies do not cover damage to any garden walls, fences or gates.
Heave and landslip
Heave is the opposite of subsidence, when the ground becomes so saturated that it swells and pushes up against the structure. It causes similar damage but, at the moment, is much less common in the UK. Your home insurance policy should also cover landslip, where the ground literally starts to slide down a slope.
Premiums for subsidence insurance
If you make a claim for subsidence, your buildings insurance premium will almost certainly rise at renewal, though your existing insurer will normally agree to continue cover.
Anyone who wants to switch insurer having made a claim would almost certainly have to seek help from a specialist as most firms are reluctant to take on a known subsidence risk. If you discover the subsidence once you have switched insurers, the Association of British Insurer's claims-handling agreement will determine whether the new or the old firm is responsible.