COMMON CAUSES OF SUBSIDENCE
Often subsidence is related to the moisture content of the soil underneath the foundations. Certain soil types are more susceptible to subsidence than others. Clay soils are particularly vulnerable since they shrink and swell in relation to their moisture content.
Vegetation near the foundations can cause subsidence because roots suck moisture from the soil, causing it to shrink. This is more of a risk during long periods of dry weather as thirsty plants push their roots through building foundations in search of water.
Water escaping from damaged drains can sometimes soften, or even wash away the ground beneath the foundations resulting in ground movement and therefore building movement.