Home sweet home?

Citation

(2001), "Home sweet home?", Property Management, Vol. 19 No. 1. https://doi.org/10.1108/pm.2001.11319aab.023

Home sweet home?

Home sweet home?

Check for subsidence and flood before buying your new home

Many people will choose their home based on the old saying that only three things matter – position, position and position. Whilst it is true that the price of a house and its future value are largely influenced by such things as a good neighbourhood, well thought of schools and proximity to transport links, serious subsidence or flooding risk can cost thousands of pounds in repairs and lost value.

But how do you know about the risk when buying a house? Unfortunately it is not as simple as commissioning a survey or seeing if any problems show up in the searches. According to David Ovadia, of the British Geological Survey, climate change and different building regulations mean that the risk of subsidence can be very different between one end of the road and the other. Even if a structural survey shows no evidence of cracks from subsidence in the past it does not mean there will be none in the future.

Most subsidence is caused by the movement of clay soils around the foundations as the clay dries out in summer (shrink) or becomes wet in winter (heave). Thus it is the change in water content that causes the problem, not simply whether or not the house is built on clay. Areas where the clay always stays fairly wet throughout the year, known as "low soil moisture deficit", have fewer problems from subsidence. But climate change means that the soil moisture deficit in the future may not be the same as in the past.

To make matters worse the building regulations in the past often failed to take into account the effects of ground movement, leaving many houses built in the 1960s vulnerable to subsidence as soil moisture deficits increase. Other causes of ground movement include mining, landslip and underground dissolving of certain rocks such as gypsum or chalk that can produce surface collapse.

Most people are covered against subsidence by their buildings insurance but that does not take away the problem. First of all, insurance companies are getting wise to which postcodes are more susceptible to subsidence and if you buy a house in one of these high-risk postcode areas, you may find that you have difficulty obtaining buildings insurance – or pay a much higher premium. Secondly, most insurers apply a £1,000 excess for subsidence claims. Most importantly, though, if you have builders in to deal with subsidence damage the hassle and disruption is likely to go on for months.

The same concerns apply to flood risk. Sometimes it is obvious that there is a risk of flooding, especially if the house is built on low-lying land with a river in sight. But often the risk is less obvious, as many people discovered to their cost in April 1998 when heavy rain across the country caused rivers to flood in areas that had not been covered in water in living memory.

Identifying such areas is possible by studying the soil. As David Ovadia explains, records of actual floods go back, at most, a few hundred years but if the soil types are of river or estuary deposits, this indicates that water has covered the area at some time in the last few thousand years, since the end of the Ice Age. This does not mean that there will be flooding in future because river banks may have been built up, but it is an indicator of possible risk and is safer than relying on historical records alone.

So a careful examination of a geological map can tell you if the dream house you are about to buy could be at risk from cracking or flooding. However, unless you have a background in geology you will find that a geological map is not an easy thing to interpret.

For most home buyers it is better to obtain professional advice on subsidence and flood risk from an organization like the British Geological Survey who, for a small fee, will give you a risk report for most areas of the country. (Contact Anthea Brown, enquiries, on 0115 9363100, e-mail: a.brown@bgs.ac.uk) Alternatively ask your insurance company if they charge higher rates for the particular postcode you have in mind and, if so, why. They will not necessarily be able to tell you if the higher rate is caused by flood or subsidence, as opposed to a high crime rate or simply a vulnerable building type, but any loading of a buildings insurance for your postcode is a clear sign to investigate further.