Shrink–swell — property hazard information

If active clay shrinkage/swelling appears to be affecting your property, inform your insurance company, mortgage lender or landlord. Get specialist advice from a suitably qualified expert such as a structural surveyor, geotechnical engineer or chartered engineering geologist.

If active clay shrinkage/swelling is not affecting your property but the area has a potential for shrink–swell clay being present this should be taken into account before starting new buildings or changes in land use:

  • take specialist advice before starting major building work
  • consider the effect of laying impermeable drives, paths, hard standing on the rainfall reaching the soil below and changing its moisture content
  • seek expert advice before planting trees near to the house
    The safe planting distance will depend on the tree species, type of house foundation and soil composition.
  • ensure foundations of new constructions or extensions are designed for the shrinkable clay soil conditions that are present
  • Do not plant potentially large trees next to the house
  • Do not remove mature trees that predate the construction of the house before taking advice. Tree management by crown reduction or thinning may be better than removal because it will maintain a stable soil moisture profile

If you have received a GeoReport the following key provides further information on the BGS shrink–swell hazard rating:

Potential for shrink–swell clay and advice for preventative or remedial action

  Hazard rating Advice for public Advice for specialist
A Ground conditions predominantly non-plastic. No actions required to avoid problems due to shrink–swell clays. No special ground investigation required or increased construction costs or increased financial risk due to potential problems with shrink–swell clays.
B Ground conditions predominantly low plasticity. No actions required to avoid problems due to shrink–swell clays No special ground investigation required or increased construction costs or increased financial risk due to potential problems with shrink–swell clays.
C Ground conditions predominantly medium plasticity. Do not plant trees with high soil moisture demands near to buildings. New build — Test for plasticity index is recommended, Possible increase in construction cost to remove possibility of potential shrink–swell problems.

Existing property — Possible increase in insurance risk in droughts or where high moisture demand vegetation is present due to shrink–swell clay problems if foundations are not suitable.

D Ground conditions predominantly high plasticity. Do not plant or remove trees or shrubs near to buildings without expert advice about their effect and management. New build — Test for plasticity index is necessary, Probable increase in construction cost to remove possibility of potential shrink–swell problems.

Existing property – Probable increase in insurance risk in droughts or where high moisture demand vegetation is present due to shrink–swell clay problems if foundations are not suitable.

E Ground conditions predominantly very high plasticity. Do not plant or remove trees or shrubs near to buildings without expert advice about their effect and management. New build — Test for plasticity index is essential, Definite increase in construction cost to remove possibility of potential shrink–swell problems.

Existing property — Significant increase in insurance risk in droughts or where high moisture demand vegetation is present due to shrink–swell clay problems if foundations are not suitable.



You may also be interested in...

  • I have received a hazard rating from the BGS and would like more information
  • Buy a GeoReport giving details of six ground stability issues for a particular area or property
  • Apply for a digital data licence for GeoSure data sets from our IPR Section
  • Contact Enquiries for more information on the GeoSure data sets and reports