Subsidence can surely be defined in different ways, however thankfully the majority of the insurance industry and professionals supporting and guiding the insurance industry have aligned to a view expressed by the Financial Ombudsman Service:
Subsidence is the downward movement of the site on which a building stands – where the
movement is unconnected with the weight of the building. Essentially, the soil beneath the building’s foundations is unstable. (FOS Technical Note – Subsidence)
The key element of the definition of subsidence which distinguishes it from “settlement” is the factor of the weight of the building. Where the property sinks “into” the site upon which it is built then this is generally indicative of inadequate design / construction. Where the site moves downward, and would have so moved even if there was no building upon it, then this is generally regarded as subsidence.
Insurance policies are generally quite specific that the cover provided is to meet the cost of repairing damage caused to the house as a consequence of subsidence of the site upon which the building stands, quite distinct from settlement of the property.
Closely associated with “subsidence” although very much rarer is “heave”. This is often listed as part of the same insured peril in domestic insurance policies. Heave is the opposite effect of subsidence, that is to say when the site upon which the building stands moves upwards (and often has a sideways element to it). As with subsidence, the term “heave of the site” (as generally covered by insurance) is quite distinct from heaving of parts of the building itself rather than the site below it. Such most often occurs when parts of the building expand as a result of chemical reactions within the building materials such as floor fill and concrete, usually brought about by moisture penetration.
Likewise closely associated to subsidence is “landslip”. Again this is often listed within the same peril in the insurance policy. Landslip is generally dramatic, obvious, needing little explanation!