Literally, every house has some foundation cracks and smaller cracks cannot cause big problems. But you have to keep in mind that even smaller foundation cracks can grow bigger. If you have larger ones then you can get it repaired from https://revampo.ca/fr/blog/fissure-fondation/.
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If you see small hairline cracks in the foundation of your building then you have to keep an eye over it. If it starts to expand or get larger then also you have to keep in touch with the general contractors. A hairline crack cannot be bigger than the width of any regular pencil line.
If the foundation of the building has structural reinforcing and rebar installation within the footings then these hairline cracks can never get bigger. If the building foundation slab itself than also there are very few chances of expansion of cracks.
If you see larger cracks in the foundation of the building then the first thing that you have to do is to measure and evaluate the crack size. You can also take pictures and make videos of the crack.
It is common to have foundation cracks when you get home construction but the only thing that you have to keep in mind is the size of the crack. A crack that is wider than half-inch can cause you problems.