The definition of subsidence is ‘the gradual caving in or sinking of an area of land’.
How can you tell if subsidence is occurring?
Depending on circumstances, there is a varying degree of effects on buildings which are astride or close to a patch of land where subsidence is occurring. Typically you would find diagonal stepped cracking through external brickwork with the more prominent separation at the highest points of the cracks. Internal symptoms include cracks in plasterwork, rucking of wallpaper and doors/windows binding within their frames.
What causes subsidence?
Subsidence is most common where finer soils are present e.g. clay soils, which are prevalent in the south east of England but also extends as far north as Hull and as far west as Exeter in what is known as the ‘Clay Belt’. Water is the primary cause of subsidence on fine soils, usually caused by a close proximity tree which can draw moisture away from soil causing it to shrink or a leaked drain which can cause fine soils to wash away from beneath foundations. A rarer type of subsidence is due to the presence of old mines beneath buildings which can cause sudden collapse.
What is the difference between subsidence and settlement?
Settlement is the downward movement of the ground as a direct result of the weight of the building acting upon the ground. Subsidence however is unrelated to the weight of the building and can happen as a result of unpredictable factors.
How do you remedy the effect of subsidence?
As soon as you see symptoms of subsidence, an expert should be called to provide a diagnosis. Once the cause has been ascertained, typical remediation processes could involve repairing drains, cutting and removing trees, underpinning the building or demolition and rebuilding parts of the building.