A documentary series on Channel 5 Sinkholes: Buried Alive prompted one customer to call just to check that their buildings insurance would cover catastrophic damage should a sink hole appear and damage their building.

On this occasion, the answer was yes. Sink holes are a form of subsidence – albeit extreme subsidence and damage caused to the building is covered by your blocks of flats buildings insurance*.  There is also the option to take a policy with enhanced cover that includes the cost of repairs to the grounds, such as car parks and hard standing, damaged by sink holes up to £10,000, with an option to increase to £50,000.

The policy also provides for alternative accommodation if the area is deemed unsafe even though the building itself isn’t damaged.   The likelihood of a sinkhole appearing, however, is thankfully very low.

What causes sinkholes?

Even though sinkholes appear to form suddenly, the underlying causes may have been brewing for some time. They are usually caused by erosion underneath the ground’s surface due to a poor drainage of water. The water dissolves soluble rock such as limestone until, eventually, it cannot support the surface any longer, and the ground collapses.

According to the British Geological Survey prone areas include the karst (limestone) landscapes of the Mendips, parts of Wales, the Peak District, and the northern Pennines including the Yorkshire Dales, parts of Dorset, Hampshire, the Chilterns and Ripon. In open countryside in these areas, old sinkholes can look like grassy depressions in the landscape.

Some of the risk factors are man-made. Leaks from sewers or pipes can cause underground erosion; and areas where tonnes of rock have already been removed by mining are more susceptible. Remember, we have a long industrial history and mines can be long forgotten. Chalk was being mined way back in medieval times and many of those pits are long forgotten.

Sinkholes have been known to be just a couple of feet across but also so big that they have swallowed up cars and buildings. The deepest sinkhole to have ever formed is in the Chongqing district of China, and it is 2,171 feet deep and 2,053 metres wide.  UK incidences are thankfully a lot smaller.

  • Last summer, a sink hole opened up in Broadstairs in Kent, to reveal a secret network of war tunnels buried underneath. They are thought to have been dug over 100 years ago, and used for training in the First and Second World Wars.
  • At the end of 2016, a woman came within inches of falling into a giant sinkhole that swallowed most of her garden in the cathedral city of Ripon, Yorkshire.
  • 2020: and here are some BBC reports of more recent sinkholes.

Sinkholes rarely strike without giving some warning in the surrounding environment or in a nearby home.  Here are a few signs of subsidence to watch for that may indicate a problem:

  • Trees or fence posts that tilt or fall for apparently no reason
  • Cracks in the ground
  • New or widening cracks
  • Separation between walls and ceiling or floors
  • Cracks in interior walls
  • Cracks around door and window frames
  • Cracked grout between tiles
  • Doors or windows that no longer open or close easily

It’s worth remembering that all buildings are subject to some settling.  Many of these signs could exist without the presence of a sinkhole, however, be aware that the presence of one or more of the above ‘tells’ may require further investigation.

* Policy limits and exclusions may apply, please see policy wording for full terms and conditions


The sole purpose of this article is to provide guidance on the issues covered. This article is not intended to give legal advice, and, accordingly, it should not be relied upon. It should not be regarded as a comprehensive statement of the law and/or market practice in this area. We make no claims as to the completeness or accuracy of the information contained herein or in the links which were live at the date of publication. You should not act upon (or should refrain from acting upon) information in this publication without first seeking specific legal and/or specialist advice. Arthur J. Gallagher Insurance Brokers Limited trading as Deacon accepts no liability for any inaccuracy, omission or mistake in this publication, nor will we be responsible for any loss which may be suffered as a result of any person relying on the information contained herein.  Please note links in the article were active at the time of publication.