When does a slab foundation crack become a problem?

When does a slab foundation crack become a concern?

The Shallow Foundation Committee of the American Society of Civil Engineers has published guidelines for evaluating cracks in slab-on-ground foundations based on the width of the crack.  Their recommendation is that if a crack is 1/16th inch wide, it should probably be looked at by an engineer.  They also state that cracks that are 1/8th inch or less do not typically indicate that the foundation is not capable of performing as intended.  Also, the Shallow Foundation Committee points out that the presence of cracks in slab-on-ground foundations “does not indicate a life-threatening, dangerous condition.”

When does a slab foundation crack become a serious problem?

Cracks due to foundation bending can result in significantly more flexibility in the slab. This means that the foundation will not do as good a job as it was intended to do to mitigate the amount of damage the soil distortion causes the house.  If the flexibility caused by foundation cracking results in structural damage to the house frame so that the frame structure can no longer carry normally imposed loads safely, then the foundation crack is a serious problem.  Also, if a crack increases the flexibility of the house so that doors necessary for an emergency exit cannot be opened and closed by a small child, that too is a serious issue that must be resolved.

Baring either of these two situations, a foundation crack may be a legitimate concern but it is not a serious problem from a structural engineering perspective.