It is common in many of the heavy clay regions of Canada for shallow foundations to move up or down by several inches. There are several other causes of foundation movement worthy of mention. Freezing of the ground is a problem in most parts of Canada. When fine-grained soils such as silts and clays or even dirty sands and gravels freeze, water is drawn up from the water table to freeze into discrete lenses and cause a volume expansion. Usually the normal winter heating keeps frost away from footings, but the possibility of frost heaving under attached garages or depressed driveways is often forgotten and results in considerable damage to light structures.
Frost action is also a hazard during construction.
A large building under construction in Ottawa was badly damaged during a cold winter period. Basement floor slabs were heaved and cracked and the movements extended up through the structure, causing distortion and cracks in partition walls. In Northern Canada there are many cases of serious distortions of heated buildings due to the thawing of ice in the permafrost under them. Even bedrock is not always reliable. The basement floor of a downtown building in Ottawa began to heave mysteriously several years after construction.