Ground instability - what does this mean?

twink1108

I have just had an environmental search come back on a property. The property has passed but it mentions ground instability which has been identified within 50metres. I'm not sure what this means and was hoping someone might be able to enlighten me! Does this usually need further investigation?

Thanks

browneyedbazzi

Ground instability is another way of saying subsidence. You can get a ground stability search which will provide more detail about the underlying geology and give you a better idea of the risk of subsidence in the house you are looking at buying. You should mention the issue to your surveyor so they can have a close look at the property for any signs of subsidence.

eddddy

twink1108 wrote: »

...but it mentions ground instability which has been identified within 50metres.

What concerns me about this type comment in a survey report is that the surveyor may tell you it is no cause for concern, and there is no real risk of building subsidence.

But is the comment in the survey report now a 'material fact' which has to be declared to insurers (and will some over-cautious insurers refuse to quote or impose special terms as a result)?

twink1108

Ive bought further reports from homecheck ground stability and subsidence one which is low risk and other seems to be infilled ponds on the map. Are these reports reliable?

Doozergirl

The Land Charges departmet at the local council will have more information on the specific location. You can call them for a chat. If your house isn't built over these ponds then there is no issue. If they are, then the house should be built with special foundations that rake into account the fact that 'solid ground' is much further down.

Ground instability is different from a natural subsidence risk, but if younaren't built directly over that area, then it is of no issue to the house.

twink1108

Hiya, thanks for all of your previous posts.

I have just had a bit more information on the ground instability but am struggling to get my head around whether there is anything to be concerned about here?

"The ground stability information in your report is derived from our GeoSure dataset. The hazards that GeoSure covers are rated from A to E where A&B are considered insignificant and C to E are low to high potential for the hazard to occur. The property you are interested in is situated very close to boundaries between the ratings and because the search will cover a distance around the property it will pick up the highest level of hazard rating within that search area.

Shrink swell clay - property located on level B, but an area of level C is mapped as 3m to the NW of the property.
Compressible ground - property is located on level B, but an area of level D is mapped as 7.5m to the NW (this is what returns the 'moderate' rating in your report)
Collapsible ground - property is located on a level B, but an area of level C is 3m to the NW
Running sand - property is located on a level B but an area of level C is 7.5m to the NW.

You should keep in mind that the geological line work that GeoSure is based on is only accurate to the nearest 50m. The data is based on the underlying geology and we can only be certain of a geological boundary where it is exposed at the surface. The boundaries beneath the surface are drawn using expert interpretation by the geologists. We ask the companies using our data in their reports to apply a 50m buffer to our data so that if the geological boundaries were not quite accurate the search would still pick up the highest rating likely for the site in question. This is another reason why your search will have returned a moderate rating even though the property is situated on a level B in the mapping.

Further information on GeoSure can be found at http://www.bgs.ac.uk/products/geosure/home.html
There is information on each of the hazards if you follow the links on this page, and the links titled 'Property Hazard Information' will give you information on each of the ratings within that hazard.

The ratings are based only on the geology beneath the site and the characteristics of the underlying rocks. They indicate the potential for the rocks to behave in a way that might cause subsidence. The ratings are not an indication that subsidence has occurred at the site or that it will necessarily occur at the site. They are also not based on a record of cases of subsidence in properties. We would always suggest that a qualified surveyor will be able to see whether subsidence has occurred or not."

Would be really grateful to anyone who thinks that they can explain this in layman's terms!

Thanks