Regardless of their construction, walls crack because they are overloaded or because the structure has settled or heaved. Vertical and angled cracks are usually caused by settlement or heaving. Horizontal cracks are more likely to be load induced or caused by side pressure.

NOTE: Surface cracks that do not pierce the wall and are not accompanied by displacement are not structural in nature and should be distinguished from the cracks discussed here.

VERTICAL CRACKS: If a wall has an upwards overload adjacent to a downwards overload, it may crack vertically so that one side rises or sinks with respect to the other (Figure 1). Vertical cracks are usually caused by settlement, compaction, or soil eroding under the footing. Overloading from above can occur when framing members fail forcing loads to areas that were not designed for them. Similar cracks can also be caused by overloads from below, such as frost or hydraulic expansion of the soil.

ANGLED CRACKS: When up and down loads are applied so the forces are offset from one another, cracks are likely to occur at an angle (Figure 2). Cracks of this type may be found when there is a major discontinuity in the soil or if a building is built on expansive clays.

HORIZONTAL CRACKS: When a wall is overloaded from the outside, as from frost, soil pressure, or improper backfill, it may bow inward and crack horizontally (Figure 3). In a block wall, the crack is usually in a mortar joint and is wider on the inner face. An additional cause of horizontal cracking may be settlement of the foundation. If a foundation is laid on top of unstable soil, the wall which lacks the proper support could drop resulting in a horizontal crack without vertical displacement of the wall surface.

Note: Surface effects such as poor grading or improperly located downspouts can increase the amount of water pushing against the basement wall.

CATASTROPHIC FAILURES: Walls are strongest in compression. As a result, they prevent a catastrophic failure which occurs from vertical loading in the absence of a horizontal component. Failure generally occurs when a horizontal component of the load causes the center of gravity of the wall to move beyond its base (Figure 4). The center of gravity is the midpoint of the mass of he wall. Unless it is specifically constrained, an object will overturn if its center of gravity moves outside its base.

Signs of possible foundation failures include:

  • Horizontal cracking or wall out of plumb.
  • Excessive bowing inward or outward.
  • Large vertical cracks (in excess of 1/4 inch).


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