No matter how much attention is given to foundations during construction, foundations will crack when the soil beneath moves, upward, downward, and laterally. Foundation and building walls are typically design to only accommodate very small amounts of movement. In terms of residential buildings, the tolerance is significantly less. Due to the relatively light load the house must withstand, the foundations and structural walls are designed accordingly, thus when movement occurs, the residential structure is more likely to crack. Most residential walls are not designed to withstand this additional ground movement.
Foundation cracks that occur in the crawlspace are most likely due to foundation settlement as opposed to lateral earth pressure from backfill. Therefore, cracks usually stair-step down the foundation. By investigating the crack size and shape, Structural Design Solutions can determine the exact cause.
The NC Building code ensures that contractors pay close attention to chimney foundations. Due to the weight of the chimney, large foundations are typically used beneath. However, depending on the workmanship of the contractors, the age of the house, or the occurrence of unanticipated bad soil beneath the footing, the chimney foundation may settle. When this settlement occurs, the chimney rotates to create either a separation between it and the house or pushes into the house. Both scenarios are equally problematic. Without proper engineering analysis and foundation stabilization techniques, the leaning chimney could be potentially dangerous. We recommend that when chimneys are leaning, please contact a structural engineer to determine the severity of the issue.
Basement Cracks & Waterproofing
Basement walls are foundation walls that retain backfilled soil. Therefore, these walls experience both vertical and horizontal pressure that can cause a variety of structural and serviceability issues that can lead to foundation failure.
Basement walls must first support the structure above, which rest directly on the walls. The walls then rest on the ground beneath. When the soil begins to move, the foundation walls will crack depending on the amount of movement that has occurred. These cracks usually appear in a stair-stepped pattern. Various other type cracks may appear as a result of soil settlement, however, the stair-stepped is the most common. By having a structural foundation inspection, the types and locations of the cracks can be examined to determine the cause.
The next type of load the basement walls must resist is lateral earth pressure, which is induced by the backfill behind the wall. When walls are over-stressed, the wall will crack in a horizontal pattern. The over-stressing or over-loading can result from a number of issues including under-designed foundation wall, hydrostatic (water) build-up behind the wall due to inadequate drainage, or potential surcharges (heavy loads resting on the ground near the walls).
If proper drainage is not provided, the walls will typically crack to relieve the (water) pressures behind the wall. Once cracked, the water is free to pass through the wall if a proper waterproofing membrane (not painted on tar or damp-proofing paint). If basements are leaking, the structural damage has typically occurred and will continue to increase in severity if the problem is not solved. It is always recommended to consult a professional engineer before a new water-proofing system is installed. A hydrostatic (water) accumulation behind the wall can cause serious damage, which will accompany the new system if not properly installed.
Interior House Cracks
Most interior wall cracks are direct indicators of foundation settlements. As the soil settles, the foundation follows. The relatively weak sheetrock cracks as the walls move. Stress relieving cracks usually follow the path of least resistance, thus typically tend to extend off of door and window corners. However, many factors affect the crack location and direction. As cracks are typically signs of wall movements, the windows and doors will soon shift as well. This condition produces addition friction at the doors and windows, thus they tend to stick and jamb.