What is natural ground subsidence?
Natural ground stability refers to the upward, lateral or downward movement of the ground that can be caused by a range of natural geological hazards, such movements are typically in the order of centimetres, but exceptional circumstances can be larger. Significant natural ground instability has the potential to cause subsidence damage to some weaker buildings and structures.
Subsidence risk in property transactions
Alice Hopkins, Environmental Consultant, Groundsure.
Subsidence is defined as the downward movement or sinking of a property. It is essential to consider the possible subsidence risks when buying a property as it can cause thousands of pounds worth of damage and can affect any property across the country.
Being aware of the risks ahead of purchase allows you to conduct further investigations if you find them to be necessary before any contacts are signed.
All of Groundsure’s environmental searches for both residential and commercial properties include the British Geological Survey’s (BGS) data on natural ground subsidence.
The BGS data assesses six datasets to provide an overall rating which will fall in to one of three categories:
- Negligible to very low
- Moderate to high
If you are concerned about potential subsidence risk we would recommend in the first instance to look around the property to identify any physical signs of subsidence – this could include cracks or movements in the walls. From there you could contact the local authority who may be able to advise you if there have been any incidences of subsidence in the past. If you are still concerned we would recommend a structural survey be carried out on the property by a Chartered Surveyor.
If you have any queries about subsidence or the findings within your report please contact our expert consultants who will be able to advise you further.
How is the assessment calculated?
The ground subsidence rating has been produced by British Geological Survey (BGS) Geologists and Geotechnical specialists and is based on the evaluation of six natural ground stability hazard datasets (shrink-swell clay, dissolution, compressible and collapsible ground, running sand and slope instability – landslides). The subsidence data provided within our reports is not property specific and is designed to highlight the highest risk ranking within a 50m buffer.
The overall subsidence rating is divided into 3 categories: Negligible – Very Low, Low, and Moderate to High.
What to do next
As this data is not property specific, further enquiries should be made to clarify the actual risk of subsidence at a property if the potential (Low, Moderate to High) has been identified. Such enquiries include;
- Obtaining a structural survey, which will be undertaken by a professional property surveyor,
- Obtain expert advice before changing the ground conditions in any way (such as building work, removing plants or shrubs),
- Contact the Building Control Department at the local authority to determine if they hold any records of previous subsidence occurring in the area.
Professional advice should always be sought prior to changing the ground in any significant way including building work and planting/removing large shrubs and trees.
The information behind the data
The subsidence hazard has been assessed using 1:50,000 scale maps of bedrock geology and superficial deposits, combined with information from several hundred thousand borehole records, scientific documents and engineering reports, photographs and geotechnical property values from the National Geotechnical Properties Database.