Problems with your house? - Shop - Institution of Structural Engineers

Subsidence is the downward movement of a building foundation caused by loss of support of the site beneath the foundation. .... your own 'second opinion'.
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Problems with your house? Cracks?

GENERAL LINE OF FRACTURING

WIDE

Subsidence? Heave?

NARROW

POSITION OF LIKELY MAXIMUM SUBSIDENCE

CRACKS CONTINUE AROUND OPENINGS

Get the right advice! What are settlement, subsidence and heave? Settlement is the normal downwards movement of a building into the

ground simply as a result of its own weight on the ground. Most new buildings experience some minor settlement during the first year or two after construction until they finally stabilise. If major structural alterations are carried out on an existing property, again some minor settlement may occur while the ground readjusts itself to the new weight pattern of the property. Settlement may cause minor cracking but this is usually not serious or progressive.

Subsidence is the downward movement of a building foundation caused

by loss of support of the site beneath the foundation. In other words, subsidence is caused by the ground moving away from the underside of the foundations of a property. This may be due to a variety of reasons which are explained later in this leaflet.

Heave is, in simple terms, the opposite of subsidence and is caused by the ground pressing up against the foundations of a property and forcing the foundations upwards.

The effect of subsidence or heave on a property is that it may develop cracks or may distort - sometimes it does both.

Why are subsidence and heave important for householders? Over the last 30 years or so properties affected by subsidence have proved difficult to sell, but things have started to change. Nevertheless, lenders and insurers are still cautious about properties that display evidence of movement. If you are likely to want to sell your property then it is important to have any subsidence or heave damage assessed, and attended to if necessary. This is best done sooner rather than later because if the problem is only identified when you are selling or buying, it may cause serious delay to your transaction. Like fire, escape of water or storm damage, subsidence and heave are standard risks covered (subject to policy wording) by the majority of domestic building insurance policies, although sometimes damage to ground bearing concrete slabs or fences or garden walls are not covered. Indeed for owners who have mortgages, it is usually a compulsory requirement of the terms of the loan that the property is insured against certain risks, including subsidence and heave. Settlement damage is not normally covered by household insurers.

What causes subsidence and heave? Subsidence is much more common than heave. The most common causes are: -

Drying out and shrinkage of clay subsoil beneath the house foundations during drought periods, such as exceptionally hot summers. Heave is normally caused by the swelling of clay during wet winters after hot summers.

- The effect of certain types of trees close to a property which can aggravate the subsidence/heave situation where clay subsoil exists. - Leaking drains and water mains can soften the ground beneath house foundations, or even wash away the material from beneath the foundations, thus causing subsidence. - Properties built close to sloping ground may suffer subsidence if the ground tends to move down the slope – even if the movement of the slope is only slight! - Chalk ground can develop cavities (swallow holes) and cause subsidence. - Mining can cause subsidence to property above and adjacent to the works.

How can subsidence/heave be dealt with? The first step is to establish that the damage is actually due to subsidence or heave. Buildings can suffer movement and cracks for many other reasons, for example due to thermal movement or differential settlement. If subsidence or heave is the cause of the damage, then three questions should be asked: -

Has the movement stopped? If it has, there is clearly no point carrying out