The main reasons for underpinning are that the structure of a property has become unstable. In turn, this happens when the foundations can no longer adequately support the building because:

• Its usage has changed, for example, because an extension has added which puts extra strain on the foundations of the main building.
• The wrong type of foundation was chosen when the property was designed arising from mis-classification of the soil type.
• The structure of the soil in which the foundations sit has changed, usually because of too much or too little water in it, causing subsidence.