The " Sink Hole " phenomenon !

A homeowner at Swansea Heads, near Newcastle got an unpleasant schock this week when a gaping great hole opened up beneath his home.    Part of the foundations were left hanging over what was called a " sink hole " that was fifteen metres wide - and twenty-five metres deep.  He quickly learned that houses in his street were over a coal mine that was closed over sixty years ago - and that most owners were unaware of it's presence when homes were built in 1996.

Repair crews rushed to fill the hole with concrete and now another sink hole has opened nearby. The entire street may be at risk but at least the damage is the responsibility of the Mine Subsidence Board.  Mining in this state is levied with a tax to fund repairs to home damaged by subsidence caused by mining.   What is unclear is how this discovery will affect home prices.    This street contains million dollar homes with marvellous water views - and even a hint of land instability can send values crashing.

Usually, council regulations are very strict where mining activity has occurred.  The type of homes permitted are designed to spread the weight load and usually this is by way of a concrete slab foundation, and the building materials permitted are carefully selected to be repairable in the event of any land movement.

Unfortunately, there is another cause of sink holes that is not covered by the Mine Subsidence Board.  In areas where the underlying strata is of a porous nature - such as limestone - water penetration can dissolve the rock and lead to vast underground caverns forming - and eventually this can lead to a cave-in.   It is a world wide phenomenon and in some cases the area is huge - and devours an entire shopping centre.

We are warned that global warming may exacerbate these incidents.   Extreme rainfall tends to increase water penetration underground - and speed up the rock disintegration.   This is not a risk covered by home insurance and usually any claim is rejected on " Act of God " grounds.

It seems that land stability is a new worry for homeowners to ponder.   When it comes to buying a building block or negotiating the sale of an existing home, we usually make no enquiry about the underlying structure of the land involved.   Perhaps future property searches may be more diligent in ascertaining that the area is entirely mine free - and that the  nature of the rock structure below is composed of the type of rock not subject to water erosion.

Land stability is a new worry for twenty-first century home owners !