Subsidence is caused by a combination of dry weather, shifting clay soils and tree movement. As the clay sub-soils dry out and crack, the ground sinks beneath the house, causing problems in the foundations and then when a hot spell breaks the rain causes the soil to expand. In hot temperatures trees will draw the moisture out of the ground, causing it to move. The expansion is rarely uniform throughout the soil and as a result the ground experiences ‘differential heave’, which can cause buildings to move and crack. Signs that your property has been affected by subsidence include the appearance of diagonal cracks, wider at the top than at the bottom, near to windows and doors or other ‘weak’ parts.
Areas most at risk from subsidence include London, the South-East, and the Midlands. 40% of homes within the M25 are at risk of subsidence. Subsidence is a major threat to houses built with shallow foundations. Most commonly seen in the construction of pre-1965 houses and particularly during the Edwardian and Victorian eras, shallow foundations are more susceptible to the problem of heave. It is estimated that more than half the national total of 3.7milion homes that are at risk. Those houses with clay near to the surface and with foundations less than two meters deep are most vulnerable.
Cracks
The first obvious sign of subsidence is the appearance of cracks. However, not all cracks indicate that there is a problem. Most buildings experience cracking at some time and there is no need to be alarmed by every crack that appears.
Cracks are not uncommon in new properties and newly built extensions. They are likely to be the result of the building settling under its own weight. These usually are nothing to worry about, nor are fine cracks that often appear in newly plastered walls as they dry out. Buildings shrink and swell naturally due to changes in temperature and humidity, which can lead to minor cracks where walls and ceilings meet. These too should not normally be anything to worry about.
What should be looked out for are small, usually diagonal, cracks which suddenly appear in plaster work inside and outside bricks at weak points, such as around doors and windows, especially after long periods of dry weather. These may, but not necessarily, indicate movement in the building´s foundations. The cracks will normally be thicker than a 10p coin, and usually be wider at the top. Doors and windows may also “stick” due to the distortion of the building.
The Royal Institute of Chartered Surveyors (RICS) is urging people to periodically check their properties for evidence of cracking. Cracks more than 3mm wide are considered to be ‘serious’ and require immediate action, especially if they pass through brickwork or stone.
RICS spokesperson Roy Ilott, said: ‘We, like the insurance companies, are expecting to see a rise in the incidence of subsidence. Finding the cracks and notifying your insurance company can be the easy part – rectifying the problem can be very complex, costly and disruptive to the household.
‘House owners should be prepared for delays as premature action can cause further problems and insurers will usually want to monitor walls for a season to assess a pattern.’
Insurance implications of subsidence
Signs of subsidence generally lead to an increase to your building insurance
premiums. Insurers determine building insurance premiums by matching postcodes
onto soil maps. Houses located in high-risk areas can be charged at least double
those in low-risk areas.
If you live in an area at risk of subsidence, the industry advice is to remain with your current insurer. Don’t be lured by more competitive prices and schemes elsewhere. Existing owners of houses in subsidence areas are less likely to experience insurance problems. The problems tend to begin when you are buying a house and trying to secure insurance on the property for the first time - many insurers refuse to cover you. Ask the existing owner or use your house purchase survey results to understand any potential problems and who the current insurers are.
Check the small print
Home owners should be extra vigilant at checking the small print and exclusions
concerning subsidence. All building insurance policies differ in the terms of
cover they provide. The excess that you have to pay before the insurer will
settle the rest of the claim varies. Typically this stands at £1,000 but
may be higher. Some building polices will not include defective designs. If
this is the case you would be advised to take action against your builder. Don’t
assume that outbuildings including garages, flooring, and peripheral features
will be automatically covered. Always check with the insurer.
The worst-case scenario is that your house needs to be ‘underpinned’. This is where the foundations are dug out and replaced. Only a few specialist insurers will take on ‘previously underpinned properties’. Specialist policies are more expensive and are likely to have more subsidence exclusions, requiring you to pay up to the first £2,500 of any claim. They may also require you to organise rigorous ‘tree management’.
Safety Checks
- Check the type of soil on which your house is built. Clay soil is the biggest risk. Chalk and granite should not subside.
- Make sure your surveyor investigates any potential underground mining works. Be especially careful in former mining areas or big tunnel digs.
- Check foundation depths. Shallow foundations are at a greater risk of subsidence.
- Look out for drainage leaks - fractured drains can either allow water to saturate the ground causing it to heave or can wash out the fine particles in the soil making the problem worse.
- Respect advice on safe tree planting distances. Seek advice from a surveyor or tree expert if a mature tree is near to your house as to whether it should be removed. Trees take moisture from the ground and can increase the risk of subsidence damage if they are planted too close to your home.
- Less commonly, problems may occur where properties are built over, or close to, mine workings.
- The Environment Agency suggests you preserve moisture in the garden by planting plants that thrive in the hot, dry conditions and do not need moisture, such as buddleia, lavender, and evening primrose. Wood chips, bark and gravel help to prevent evaporation and weed growth saving water.
- Keep gutters and drains clear and clean so the soil beneath foundations is not washed away.
- Be careful about greatly increasing paved areas as this can cause a reduction in the amount of water percolating into the subsoil.
- Contact your insurer immediately if you spot any suspicious cracks that are wider than a 10p piece.
- A structural survey, that should identify any potential problems, is a must before you buy a home at potential risk of subsidence.
- As soon as any signs of subsidence occur, including suspicious cracks in the wall, ceiling or floor, contact your insurer and surveyor immediately.
How subsidence is corrected and repaired
Fortunately very few cases of subsidence are likely to require under-pinning - the strengthening or deepening of building foundations. Generally, further damage can be prevented by the professional removal or pruning of trees, repairing drains, or by localised repairs to brickwork. Then internal decorations will be renewed to complete the job.
But if underpinning is required then drastic action is required which involves the deepening of the foundations. The mere fact that a house has been underpinned can cause problems when the owner comes to sell, unless it has been carried out by a reputable building company.
The Royal Institution of Chartered Surveyors says underpinning is "a lengthy, costly and disruptive procedure that can cost anywhere between £5000 - £50,000 or more."
But only 20-30% of properties suffering from subsidence need underpinning and the Institution of Structural Engineers recommends that it only be used as a last resort.
Partial underpinning of a property or block of properties, so that the underpinning is on a different soil area, can exacerbate the problem as the remainder of the block or house may be adversely affected by future adjustments.
On finding a crack, householders should immediately notify their insurance company, or their landlord, and make a claim. However the process can become stressful as the claim may well involve many parties – the insurer, the owner, the loss adjuster (whose job it is to abate the process in favour of the insurer), a building surveyor or engineer, and the building contractor.
‘Our experience is that because it is such a slow process there can appear to be little co-ordination between all the parties and owners often feel they are ‘piggy in the middle’. We would advise them to step back and let the experts get on with the job,’ added Roy Ilott.
Remember
- Insurance is only there to remedy damage already done, it will not cover the costs of preventing further damage occurring.
- If owners choose not to underpin their property, they will not be required to have remedial works signed-off by building regulations and therefore when they come to sell their property it will not show up on any future searches made on the property. In June 2007, when the Government launches the Home Information Pack, this situation will change as people will be expected to declare all building works undertaken on a property during their ownership.
- To help members of the public deal with the issues associated with subsidence,
RICS has produced a free brochure entitled: ‘What to do when the earth
moves’.
It is available from the RICS Contact Centre, telephone 0870 333 1600.
Get
a home contents insurance quote.
