The foundation walls are connected to the top of the footings. The purpose of a foundation is to carry the weight of the house structure down through the foundationlist to the footings.
Whatever their construction, (concrete, brick, concrete blocks, etc.), foundation walls crack because of lateral force, settling, heaving or uneven loads (more weight than designed on a specific section of the foundation), of the foundation walls. Natural forces such as earth quakes can also be a contributor in earthquake regions.
To begin your inspection, use a pad and pencil while observing the exterior foundation. Make notes of cracks and their locations. When inside the lower level, you will want to try to locate them on the inside. If the crack goes entirely through the foundation it may be a red flag. Small hair-line cracks that do not go through the foundation wall are common and nothing to worry about; they may have been caused by shrinkage of the concrete or mortar joints.
A found crack sometimes has a similar type crack on an opposite wall of the foundation. Similar cracks on opposite walls may have the same cause, with the exception of horizontal cracking caused by a lateral force.
Types of Cracking
Vertical and 45 degree cracking is usually caused by settlement and heaving. Horizontal cracking is commonly caused by side pressure on the foundation, such as hydrostatic pressure (a lateral force). Surface cracks that do not go entirely through the wall and with no signs of displacement are not normally a structural defect. Isolated vertical cracks that do not extend to the lower edge of the foundation wall are usually shrinkage cracks. They are caused by the concrete shrinking during curing.
Causes of Horizontal Cracking
The foundation should act as a retaining wall, resisting lateral pressure of the soil on the outside of the basement or crawl space. If the foundation does not provide enough lateral support, the walls will deflect inward and create horizontal cracking. Some of the causes are foundation walls that are too thin or do not have, (or not enough), reinforcement, such as rebar in the concrete foundation, backfilling the foundation too soon before the foundation has a chance to fully cure, or during back filling if big stones or hard frozen chunks of ground were dumped against the foundation.
Causes of Heaving Foundations
Heaving cracks in foundations made out of brick, blocks, or stones,(not concrete), will generally have cracking in the form of a step, called “step cracking”. Step cracking usually follows the mortar joints in these materials.
In concrete foundations, cracks from heaving are usually vertical and are wider at the top of the crack than at the base.
Some areas of the country have expansive soils, which increase in size when they absorb water, causing heaving cracks. Moisture added to dry expansive soils, say from a sudden down pour, will drastically change the volume of the soil and cause serious heaving problems as well as structural damage in some cases. When the expansive soil dries, the shrinkage can also cause a pulling effect on the foundation. The method of prevention is to maintain the soil moisture content, by keeping the soil as dry as possible along the foundation. This can be achieved by proper grading around the perimeter.
Causes of Foundation Settlement
Settling of the soil under the foundation is usually the cause of settlement cracks in the foundation walls. Cracks caused by settling resemble cracks caused by heaving, except the crack is wider at the lower end of the crack.