Subsidence can be caused by a number of things. One of the biggest causes of subsidence cracks is clay soil. Whenever it rains, clay soil absorbs the water, swelling and pushing up against the foundation.
Once the rain dries up, the clay shrinks again and the ground settles back into position. All this movement is normally too much for walls and foundations to take, and huge cracks begin to appear.
Certain vegetation can also case havoc with your house. Big trees and thirsty shrubs need water to survive, so they take the moisture from the clay soil – causing them to shrink even more. This occurs especially during long periods of dry weather.
But Mother Nature is not all to blame. Leaking or damaged drains can make the ground beneath the foundation mushy or wash it way, also causing subsidence damage to your property.
Another, albeit less common, cause is if a house is built over, or close to mine workings. The blasting and shaking could also cause huge structural problems and leave you to deal with the cracks.