Does anybody have some experience building over shallow mine working and know what the pit falls (sorry for the pun) are?
How does building over old mine workings, to the Mine Subsidence Boards standards, affect the end sale price or value of the newly built property?The footings for any buildings over a mine subsidence area should be designed to allow for reasonable subsidence movement, in accordance with the requirements of the Mine Subsidence Compensation Act (1961). They will therefore be more substantial and therefore more expensive than footings for equivalent buildings on standard foundation material. This therefore adds to the cost of the buildings.
Typically, houses in subsidence areas show symptoms of movement such as hair line cracking on internal and external walls, and binding of doors and windows. Cracking may be more severe where greater subsidence has occurred. These are the accepted risks for living in a coal mining district.
You should take into account the age of the property (the newer the better, as footing design will be more to current standards), the housing demand in the area, and the expected life of the mine (for future demand).Thanks Trev for your comments,
The site I am interested in is directly over a mined 5m coal seam less than 25 meters below the surface. The mine closed in 1960, There also appears to be a fairly large amount of “fill” on the land left from the mining activity.
My project would involve building up to 4 houses and selling at 2 or 3 on completion. I am most concerned about the degree resistance potential buyers might have to buying property on such land. Do banks worry about lending for such properties and are there any ongoing insurance issues?
Also would there be any lasting liability that I (as the developer) might have if a sink hole should appear and damage a house that I sold.It looks like you will need approval to build from the Board. This should indicate whether they think there are likely to be any problems.
The consulting engineer who does the footing designs for any houses in a mine subsidence area will need to factor subsidence into his designs. He should also recommend other design features (e.g. articulation joints, avoidance of brickwork above doorways and window openings) to minimise any damage due to subsidence. This will most likely add to the building cost, compared to a building with standardised footings. If there is any fill on the site it will be recognised in the soils test and the engineer's recommendations will include allowance for that as well. The Mine Subsidence Board provides design guidelines that the consulting engineer should be aware of.
The Mine Subsidence Board will endorse the designs when they are submitted for Development Approval. Provided the houses are built in accordance with the consulting engineer's recommendations and are endorsed by the Mine Subsidence Board you should not have any liability for future damage due to subsidence. Should any damage occur due to subsidence the owner could apply to the Board for compensation.
With documented evidence that the houses have been built to minimise subsidence and have been approved by the Mine Subsidence Board, the loan approvals and reaction from potential buyers should be favourable.
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