In Quebec, foundation subsidence is a widespread problem. In Greater Montreal, as in most of the most populated areas of the province, the main causes of foundation degradation are related to three main factors: the nature of the soil, the quality of the concrete or backfill or a combination of both.


These three causes manifest themselves more or less visibly according to the geographical areas and the seasons. From Ottawa to eastern Quebec, more than two-thirds of the buildings are built on the clay deposit of the ancient Champlain Sea, composed of a clay that is particularly sensitive to rain/drought cycles. Depending on weather conditions, soil drought cycles, especially in summer, result in a loss of volume that can cause buildings to subside.

A phenomenon that could also be accentuated with the climate changes observed, periods of extreme rain and drought can multiply. If this is the case, the repetition of these cycles will further weaken the stability of the foundations in such an environment.

Secondly, it should be noted that many buildings have been built on old landfills after backfilling, on old rivers or on sites whose soils, for lack of sufficient density, do not have the bearing capacity to build there.

Finally, the quality of the materials used can compromise the longevity of foundations.  It should be noted, for example, that the useful life of foundations built between 1900 and 1930 is only 75 to 100 years, the dosages being often irregular and the concrete, of poor quality.  It is therefore not surprising that a large number of owners are concerned today.


The movements of the building, either uniform or differential, can be signs of a settlement of the foundations. It is then important to analyze the cause to determine if it is a movement due to the ground or  to the structure of the building itself.

Often, cracks, water infiltration or uneven floors highlight the structural weaknesses of the building.  This can, for example, occur as a result of a  drought or a change in the building environment.  We must also examin the cracks in the finishes (wood, floor, drywall, moldings, brick, concrete, etc.), each material having its own characteristics.

It is also necessary to check if the opening and closing of doors or windows is made difficult. It is obviously a question of taking into account all the relevant signs to be able to make the right diagnosis.


If it is the nature of the soil that is involved, the solution is often to drive steel piles to bedrock, support and stabilize the foundations, which should permanently solve the problem. If the cause is the quality of the concrete of the foundations, there may be a need to repair or even replace the foundations.

If you notice any signs that may suggest the degradation of your foundations, do not hesitate to contact Bisson Expert. Whatever the origin of the problem, the visit of a specialist on site will make it possible to make a serious diagnosis and to propose the appropriate fix. 

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