There is an old saying: “Concrete is guaranteed to do three things—get hard, turn gray, and crack.”
Small cracks in concrete foundations occur due to concrete curing and normal expansion and contraction of materials as temperatures change. No matter how thick the walls, no matter how solid the ground on which the house is built, some cracks will occur. Small, hairline cracks do not affect the strength or safety of the concrete.
Warranty coverage for cracks in concrete foundations are specific to the type of concrete work and its location. Consult your Standards of Performance for more specific information.