Sinking floors and uneven floors are usually caused by subsidence due to water in the soil or ground movement. This means that the ground beneath your flooring may be moving in response to a variety of factors such as un-compacted fill, voidage from compromised plumbing services, such as storm water, sewer, or leaking water mains. This will result in the moisture content of the soils changing: in reactive clays, this will result in the ground expanding and contracting forming voids; and in sandy loams and sands, these factors will contribute to washouts, again compromising the load bearing.
