Advice from RICS on subsidence
RICS is urging house-owners to keep an eye on their properties, as a winter of drought followed by a hot, dry summer could see their homes cracking under the strain.

Subsidence, caused by the loss of water from shrinkable subsoil, brought about by a period of high temperatures and low rainfall, is a major threat to houses built with shallow foundations.

Houses built pre-1965 tend to have shallow foundations which are more susceptible to the seasonal changes in the top metre of soil.

‘Subsidence’ is due to shrinkage of the soil below foundations while ‘heave’ arises when a dry spell breaks and rain causes the soil to expand.

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.

RICS is urging people to periodically check their properties for evidence of cracking.

Cracks over 15 -25mm wide are considered to be ‘severe’ and require 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."

Action to permanently correct subsidence is drastic and involves the deepening of the foundations in a process known as underpinning.

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 and the appropriate building regulation certificates are available.

Partial underpinning of a property or block of properties, so that the underpinning is at different depth or on a different soil type, 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 manage the claim on behalf of the insurer), a building surveyor or engineer, and the building contractor.

Roy Ilott adds:

"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".

Subsidence – the underlying facts:

Things which exacerbate the problem include:

• An increase in paved areas, causing a reduction in the amount of water percolating into the subsoil.
• Fractured drains, which can either allow water to saturate the ground causing it to heave or can wash out the fine particles in the soil possibly leading to subsidence.
• Trees close to houses are also a threat as they take water from the soil through their roots and exacerbate any shrinkage caused by dry periods.
• 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 August 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.

Roy’s top tip is to make sure you have adequate insurance which is based on the cost of rebuilding, not the sale value of your home.