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All construction must be based on foundations. They are the ones who carry the house and ensure its stability. And when cracks appear in the foundations, the whole structure of the house is weakened.

What is the role of foundations in a house?

Foundations can not be seen. They are buried in the ground and the house rests on them. They ensure the stability of the building by evenly distributing building loads on the floor. The charges are the weight of the house, all that it contains and its occupants. But it is also the forces acting on the building like the wind, the weight of the snow, etc.
Foundations allow your home to resist all these constraints without moving unless they are weakened and cracks appear.

Why foundations crack?

Foundations must meet very strict standards. To install them, it is always necessary to look for a soil having a good bearing capacity that is to say a stable ground, the most rigid possible.
It is the study of the soil that will determine the type of foundation: superficial, semi-deep or deep foundations. It is sometimes necessary to go several meters under the ground, a bearing ground. Foundations too superficial or poorly done are sources of major disorders.

But other elements come into play and cause differential settlements and thus cracks in the foundations:

  • The type of buildings to build. The foundations of a detached house are not the same as those of a skyscraper! A house built on a semi-basement will be more likely to crack than one built on a full basement. Unless the foundations take into account this difference in load distribution (The part with basement is heavier).
    Similarly building a terrace on the wall of the house can cause an imbalance if the foundations of the new construction are not strong enough.
  • The nature of the soil: Clay, sandy, rocky soil or heterogeneous soil with different lift depending on the location. Under the weight of the construction, the soil will settle differently and thus lead to the appearance of cracks.
    A construction performed on embankments poorly compacted or of different natures causes the same problems.
  • Climatic conditions: The alternation of rainy episodes followed by droughts lead to land movements especially in clay soil. Soil swells, shrinks, then swells and shrinks, etc. All these movements move the foundations.
  • The state of groundwater: Large fluctuations in the level of groundwater can affect the stability of the soil and thus the foundations (rain, drought, pumping, diversion of watercourses).
  • The environment is just as crucial: Major excavations right next to an existing building can weaken the foundations.
    Achieving a drainage on the surrounding grounds the construction will change the nature of the soil that will dry up.
  • The freeze: The foundations must be frost free. Depending on the region and the altitude, they are therefore more or less deep.

Failure to comply with these rules will result in the appearance of cracks in the foundations. "A differential settlement of 1 cm between two support points of 5 m apart is enough to cause a crack..."

The particular case of swelling clays

This type of clay is particularly "destructive" for buildings. Very sensitive to water, they swell and rise with the rain to retract and settle in drought. The withdrawal can reach ten centimeters. Particularly put to the test, foundations move, crack and cracks appear in the walls of the building.
The risks associated with the shrinkage-swelling phenomenon of clays is the second compensation item for natural disasters of single-family houses. In some regions, a Risk Prevention Plan indicates the precautions to be taken for this type of terrain.

How to repair cracked foundations?

When foundations are reached, it is imperative that consolidate: Undercover work, installation of micro piles, injection of resin under the foundations, etc. It is only when the foundations are stabilized that cracks in the facade can be capped.
When cracks appear always warn your insurer. Do not hesitate to seek the advice of an independent expert. Also notify your town hall especially if your municipality has been classified as "natural disaster zone".

Video Instruction: How to Repair a Crack in a Concrete Foundation - This Old House