Mining, Sinkholes and Subsidence – Avoiding the Sinking Feeling of a Money Pit

When buying a property in the South East many people will not think of mining or subsidence as a real risk. This is partly because industrial age mining of coal and tin has never been an industry for the home counties of Hampshire, Surrey, Sussex and Berkshire and the perception that where a building has stood on ground for a number of years it has ‘stood the test of time’ and the ground is unlikely to slip beneath it.

Potentially these are grave errors and too much reliance on this reasoning could be disastrous.

If you look at any town you will see a diverse multitude of buildings. All the materials to construct those buildings – bricks, cement, steel, glass and wood – originally came out of the ground. Take Guildford as an example. There are houses for its 150,000 population, a cathedral, science park, shopping centre and university, all of which came out of the ground.

Clearly somewhere in this country or perhaps abroad there are some holes in the ground corresponding in size with all these structures on the surface. But surely these holes in the ground are elsewhere and not here?

Again a dangerous assumption. As an example: over thousands of years, chalk has been excavated through deneholes. These are vertical shafts in the chalk dropping maybe twenty metres with a bulbous excavation chamber at their foot (think of the shape of a lightbulb). When the digger back in prehistory had finished their excavations, the entrance was sealed with wood. Over time that wood has rotted leaving a deep and widening hole beneath.

The drive of industrialisation has gone beyond simply removing items from the ground. There is an entire infrastructure of pipes and wires beneath the ground which break and release substances which may be considerably more noxious than water.

The ground itself is not a uniform entity but made of different layers each of which reacts differently to the incursion of water or something worse.

Sinkholes caused by broken sewers occur frequently under roads, causing traffic disruption but the scale of this is minor compared to some of the extreme sinkholes which have been seen in recent years. Last year a 6 metre deep sinkhole opened in Norwich and in 2014 a 9 metre sinkhole, which swallowed a car, opened in Buckinghamshire. This hole was not under the main road but the driveway of the house just a few feet away from the building.

So what can a property buyer do to protect itself against this potential risk? There are three key steps here:

First, a thorough desktop environmental search. These search available historical records. There are some key indicators of potential risk (old maps showing industrial sites or in the case of deneholes, the edges of old fields) and if there are contrary indicators such a search will flag these up.

Secondly, look very carefully at your insurance policy and speak to your insurance advisor to find out whether or not sinkhole damage would be covered. While policies may refer to subsidence the insured risks do not specify what a sinkhole is. Please bear in mind that insurance only covers damage to your property not, for example, any reduction in value because a nearby sinkhole has devalued properties in the area.

Thirdly, there is no substitute for having a proper survey carried out on your own behalf and not relying on the mere valuation provided for the benefit of a mortgage lender.


John Guthrie

Senior Associate, Commercial Property

John started his career at Hart Brown in 2016. He is a Commercial Property Senior Associate with 21 years post qualification experience in property. He...

John Guthrie Associate, Commercial Property

Senior Associate, Commercial Property

John Guthrie

John started his career at Hart Brown in 2016. He is a Commercial Property Senior Associate with 21 years post qualification experience in property.

He is a member of the Law Society and has written articles for the local press in Kent, Sussex and Surrey.

John's specialisms:

The full cycle of business leases, buying and selling businesses as a going concern, specific expertise in the leasing and disposal of licensed premises, development work and residential leasehold extensions.

His most memorable case:

Handling the property aspects of a £20 million company acquisition and restructuring the leaseback arrangements to achieve a substantial SDLT saving.