The research includes a report commissioned by esure from the British Geological Survey (BGS) which describes how new driveways - and other impermeable surfaces such as patios - can cause rainfall to 'run off' into drains rather than penetrating lawns or flowerbeds where it will seep down to reach tree roots. This can then create the conditions for subsidence as roots searching for water upset the moisture balance in the soil that underpins nearby foundations.
The number of properties in Greater London at risk from this phenomenon is estimated by esure home insurance to top 100,000. This is equivalent to the 7% of homeowners in the South East who have already converted their front gardens into parking spaces (source ICM) - plus their direct neighbours - as a percentage of the estimated half million homes in the Greater London area built on London Clay with a large tree nearby (source: Addressology 2006).
Nikki Sellers, head of home insurance at esure, said: "It is very appealing for homeowners in busy streets to create a bespoke parking space for their property. Unfortunately, for houses with a street tree or large front garden tree nearby this can significantly increase the risk of subsidence. A dedicated space may increase the value of your home but subsidence damage will do quite the reverse.
"It is essential that driveway or patio conversions are sympathetic to the fact that nearby trees will always need moisture."
Lee Jones, of the British Geological Survey, said: "It is a simple fact that trees need moisture, so anything that deprives them of moisture over time in clay soil areas can create the conditions for subsidence. The dramatic rainfall we have seen recently will only reach trees if the ground above allows the water to penetrate the soil and reach their roots."
The risk of subsidence is further compounded if homeowners have laid impermeable surfaces such as concrete driveways or patios rather than gravel or brick paving which still allow some water to filter through.
Without adequate moisture entering the soil, esure's research concludes that tree roots may extend under properties in search of moisture. In clay soil areas - particularly during dry periods - this can contribute to soil 'desiccating' under properties. This can significantly increase the chances of subsidence, particularly if a number of adjacent neighbours all do the same thing, effectively cutting off one of the main water sources for a tree.
