Frequently Asked Questions
Below are some of the questions that most commonly worry homeowners. Click on the question to bring up the answer. Technical terms are highlighted and moving your mouse pointer over them brings up a brief explanation in the top left corner of your browser window.
What causes subsidence and heave?
How can I tell whether the cracks have been caused by foundation movement?
Why is subsidence and heave damage so common?
Why are some properties affected, when others in the same street remain undamaged?
Are nearby trees causing problems or are they likely to cause damage in the future?
Should I prune trees, or remove them altogether?
When should I start to worry about the damage?
When should I tell my insurer and how do I make a claim?
What will it cost me to make a claim and what is covered?
Will my house need to be underpinned?
What investigations will be needed and how long will it all take?
Will I have to arrange the repairs myself?
Should I avoid buying a house built on clay?
Will a claim for subsidence damage make it difficult to sell my property?
What causes subsidence and heave?
Much of the UK's housing stock is founded on what are known as shrinkable clays. Such clays are strong enough to support a building of four storeys on a simple foundation. But they shrink when their moisture content decreases and swell when it increases. Slight movement of houses founded on these soils is therefore inevitable as a result of seasonal changes in moisture content: downward movement or subsidence occurring during the summer and upward movement or heave during the winter. However, these movements rarely cause damage because the whole house is affected more or less equally. Damage is therefore usually associated with trees, which enhance the extraction of moisture locally, especially during prolonged periods of dry weather. Conversely, removing a large tree can cause heave as moisture gradually returns to the soil. Shrinkage and swelling of the surface soil are not the only causes of subsidence and heave, but they are by far the commonest. Other causes of subsidence and details of why clay soils shrink and swell can be found in Chapter 3 of Has Your House Got Cracks?
How can I tell whether the cracks have been caused by foundation movement?
It can be very difficult to distinguish damage caused by foundation movement from other causes, especially where damage is relatively slight - typically, where the cracks are no wider than 2 mm. Nevertheless, there are a number of characteristics to subsidence and heave damage and these are summarised in Table III of Has Your House Got Cracks?. Wherever possible measurements should be made to confirm that there is a significant slope to floors and brick courses before jumping to the conclusion that the damage has been caused by foundation movement. For further details see Distortion Survey, in Chapter 9 of Has Your House Got Cracks?
Why is subsidence and heave damage so common?
The incidence of damage caused by clay shrinkage increases dramatically during dry summers - so called "event years". Recent event years include 1989, 1990, 1995, 1996, 1997 and 2003. Following an event year, there is a tendency for claim figures to remain at a relatively high level suggesting that many homeowners are prompted to report damage because of media coverage or because they are aware that their neighbours have had problems. In many cases, the damage reported may be unrelated to foundation movement, but if the affected property is founded on shrinkable clay it is likely to be moving seasonally making it difficult for investigators to distinguish between genuine subsidence and general wear & tear.
Why are some properties affected, when others in the same street remain undamaged?
Most subsidence damage is influenced by a combination of four main factors: soil type, weather, vegetation and foundation depth. In certain areas, soil properties can vary over relatively short distances. Foundation depth can also differ from property to property, especially where the age of construction varies. Most importantly, the zone of influence of individual trees will depend on a number of factors such as the availability of moisture and competition from other vegetation. However, the fact that the damage is restricted to a single property often suggests that other factors may be involved. For example, where a property has been damaged or distorted in the past, relatively small seasonal movements can open up existing defects. For further details see What caused the movement? in Chapter 9 of Has Your House Got Cracks?
Can I do anything to reduce the risk of damage occurring or to prevent existing damage from worsening?
For existing properties in shrinkable clay areas, care should be taken to keep certain trees, that are known to cause damage, at a sensible size if they are close to the building (see Table I of Has Your House Got Cracks?). Care should also be taken when planting new trees or removing large trees close to the building. Carrying out structural alterations or excavations near foundations can make a property more susceptible to damage and laying drives or paths can alter desiccation by reducing the supply of rain water (see Chapter 5). For new buildings and extensions, suitable foundation design complying with current regulations and guidelines will dramatically reduce the risk of heave and subsidence damage (see Appendix C of Has Your House Got Cracks?).
Are nearby trees causing problems or are they likely to cause damage in the future?
As a rule of thumb, the more damaging trees should be kept at least one tree height away from buildings founded on shrinkable clay. When planting a tree you should therefore take its mature height into consideration. Broad leaf trees are more likely to cause damage than evergreens (see Table I of Has Your House Got Cracks?). Because of their high moisture demand, oak, elm, willow and poplar are notorious for causing damage. For further details see Effect of trees in Chapter 3 of Has Your House Got Cracks?.
Should I prune trees, or remove them altogether?
Where a tree is thought to be causing a problem and it is younger than any part of the house, it is normally safe to remove it altogether. Where the tree is older than the house, or any additions to it, do not remove the tree without seeking professional advice. In such cases, substantial pruning (crown reduction) is likely to be preferable. However, once a tree has been cut back, it will grow vigorously and to be effective the treatment has to be repeated every other year (see Chapter 11 of Has Your House Got Cracks?).
When should I start to worry about the damage?
In the vast majority of cases, cracks caused by clay shrinkage during dry weather are unlikely to be of structural significance, except for vulnerable features such as brick arch lintels. Many cracks will close once there is a return to wetter weather and they can then be repaired as part of routine maintenance and decoration. Where damage is Category 3 or more in severity (see Table III of Has Your House Got Cracks?), or if the problem is not thought to be caused by clay shrinkage, it is important to seek professional advice (see What should I do? in Chapter 7 of Has Your House Got Cracks?).
When should I tell my insurer and how do I make a claim?
You should report to your insurer any damage which is thought to be the result of foundation movement. Table II of Has Your House Got Cracks? lists the characteristics of subsidence damage and will help you decide if foundation movement is to blame. You can report damage without making a claim and, where cracks are not severe (see previous question), you may simply state that you intend to repair them. If you do make a claim, your insurer may appoint a loss adjuster whose first task is to establish whether or not the claim is valid. If it is, a suitably qualified professional such as an engineer will be required to investigate the cause of the damage and advise on remedial measures. Many insurers appoint this investigator directly. For further details see Chapter 7 of Has Your House Got Cracks?.
What will it cost me to make a claim and what is covered?
The cost to you of making a claim is normally limited to the policy excess, generally £1000 or £2000. Where the investigator is appointed by the insurer, you will have to pay this amount only if it is decided that there is a valid claim and that repairs are needed. Where liability for damage is denied by your insurer, any costs that you incur will be at your own risk until such time as the claim is proved. Under the cover provided by most `Buildings' policies you are entitled to `reinstatement'. This means that the house will be returned to its pre-damaged condition without any deduction for wear & tear, provided that the house has been well maintained and that the level of insurance is adequate. The insurer will also wish to satisfy itself regarding the age of the damage and whether previous problems were disclosed when the policy was taken out. A failure to disclose such information or comply with other insurance policy conditions may entitle the insurer to reject the claim
Will my house need to be underpinned?
In most cases, it is possible to identify the cause of the subsidence and to take appropriate action to eliminate or reduce it. For example, the implicated tree can be removed or the leaking drain can be repaired. Once the cause of the subsidence has been dealt with, the foundations should continue to perform adequately and appropriate repairs can be carried out. Underpinning, which is a technique used to improve or replace the existing foundations, should be considered as a last resort that has only limited application to domestic subsidence damage. Unfortunately, underpinning is often recommended for the wrong reasons and a framework for deciding when it is the right solution is presented in Table IV of Has Your House Got Cracks?. For further details see Chapters 11 and 12 of Has Your House Got Cracks?.
What investigations will be needed and how long will it all take?
The investigation of subsidence damage can be a protracted affair taking 18 months or more. In recent years, however, advances in knowledge and streamlining of claim procedures have allowed this period to be reduced significantly. Ideally, any investigations that are needed to help identify the cause of the damage should be undertaken as part of the initial inspection. The investigator should then specify any remedial works that are needed, such as tree removal or drainage repairs, without unnecessary delay. Although a period of monitoring will be needed to confirm that this action has been effective, level monitoring as opposed to traditional crack monitoring allows this period to be reduced to about 6 months. See Chapters 9 and 10 of Has Your House Got Cracks? for further details of the investigations and monitoring.
Will I have to arrange the repairs myself?
In most cases, the investigator will see the claim through from start to finish. This includes agreeing the scope of repairs and decorations with you and, where appropriate, with your insurer. The procedures involved are described in Chapter 14 of Has Your House Got Cracks?, and Chapter 15 offers some advice on what to do if things go wrong.
Should I avoid buying a house built on clay?
All houses founded on clay soil move up and down slightly over the course of the year. But, in the vast majority of cases, these movements are no more significant than the thermal expansion and contraction that affects all buildings. Cases of structural damage are rare and are nearly always associated with large trees. Damage of this kind is generally avoidable by taking appropriate action before the tree causes damage. See Chapters 5 and 16 of Has Your House Got Cracks?.
Will a claim for subsidence damage make it difficult to sell my property?
In principle, a previous insurance claim for subsidence damage should not reduce your home’s market value, because it will have been reinstated to its former, pre-damaged condition and all appropriate measures will have been taken to prevent a recurrence of the damage. In most cases, the existing insurer will continue to offer cover under normal terms and conditions and will provide a Certificate of Structural Adequacy. Nevertheless, personal expectations vary and some potential buyers will inevitably be put off by a previous claim for subsidence damage, especially where the property has been underpinned. See Chapter 16 of Has Your House Got Cracks? for further details.
