Cracks in a concrete foundation can't be prevented. They occur because of thermal contraction, drying shrinkage, and settlement of the soil beneath the foundation. Vertical cracks caused by your home's foundation settling can indicate a structural problem, depending on factors such as width, location and number of cracks that occur. In most situations, homeowners should call a professional to inspect the cracks and the foundation.
Settlement cracks are caused by your home settling into the soil. This can be a problem if the settling is caused by damaged or inadequate footings or if the soil around your home is saturated with water or is extremely dry. When the soil is saturated, the groundwater rises and puts pressure against the foundation walls and floors, causing cracks. When the soil experiences long periods of drought, it shrinks as the water evaporates, and this causes the foundation to sink. This sinking may occur only at one end of the foundation, at both ends, or in the middle. In all three cases, the concrete cracks.
Settling versus Shrinkage
Vertical cracks occurring between two foundations may be caused by varied settlement between the two foundations. For example, where a garage is added onto an existing structure, settlement cracks can occur if the garage is built on footings that are shallower than the existing structure's foundation. Almost straight or meandering vertical cracks in poured concrete, brick, or masonry foundations that have an even width and occur intermittently are usually caused by shrinkage of the concrete rather than settling. These cracks usually pose little risk to the foundation's structural integrity.
Vertical foundation cracks typically appear in multiples, and are often seen in more than one area of the foundation. If you notice a vertical crack, no matter how small, inspect the entire foundation to determine if you have more than one crack. Continue to check the foundation regularly for new cracks. If new cracks continue to appear, this may indicate problems in the soil or the concrete itself, and should be inspected by a professional.
Vertical cracks that are wider at the bottom of the crack than the top in any foundation indicate significant settling has occurred in the soil and may indicate that the foundation is at risk of collapsing. Cracks that are the same width down the length of the crack, but that are higher on one side of the crack or wall than the other, indicate differential settlement in the foundation's footings. This may be a sign of serious defect in the home's foundation. It may also indicate that a footing has broken and the foundation has settled straight down on one side of the crack. In poured concrete and concrete block walls, cracks that are wide at the top typically mean that the ends of the foundation are dropping or that the middle is rising. In all situations, a structural engineer should inspect the foundation to determine if repair is necessary.