Misconceptions About the Common Crack
Are you concerned about cracks in your house or building? Cracks can be unsightly, but are they an indication of serious structural distress or possibly unsafe conditions? Cracks appear in brittle materials such as concrete, sheetrock, tile, wood, stone, brick, and stucco. Structural distress does cause cracks, but the vast majority of cracks are not structural in nature.
Cracks are most commonly caused by expansion and contraction of building materials due to changes in moisture content and temperature. These types of cracks do not represent a structural concern. Concrete, mortar, grout and stucco can shrink and crack for months after construction as they slowly dry and lose moisture. Shrinkage cracks in concrete floor slabs are expected and very common, and do not compromise structural integrity. Wood framing, wood floors, and trim can also shrink as the wood dries and becomes acclimated to lower inside humidity. Temperature changes cause construction materials to expand and contract daily and seasonally. For example, the temperature difference between the exterior and interior sides of a wall can cause as much as 1/2 inch of bowing stress daily. The temperature in an attic can fluctuate daily, by as much as 100 degrees Fahrenheit.
|The temperature in an attic can fluctuate daily, by as much as 100 degrees Fahrenheit.|
Due to this fluctuation, cracking is expected; which is why builders use construction joints in materials such as concrete, brick, stucco, and tile. The joints allow for stress relief in the form of controlled cracking along a pre-determined alignment. Cracks often emanate from doors and windows since these wall openings act as large construction joints to relieve stresses.
It is important to note that all foundations on soil move to some degree. Soils that support the foundation may consolidate and settle due to the weight of the house. They may also shrink and swell due to soil moisture fluctuations, or heave due to frost activity.
In new homes and buildings, it takes time for soils to adjust to the new foundation and landscape irrigation, which is why builders prefer to wait until the end of the typical 1 year workmanship warranty period to make any repairs.
Most foundations are designed for up to 1 inch of soil movement; however, in highly expansive soil areas, slab foundations can be designed for up to 4 inches of soil movement. When the foundation moves, the entire structure moves with it causing some degree of racking, distortion, and cracking. The foundation should be designed to maintain structural integrity as it moves, but some cracking is inevitable. In new homes and buildings, it takes time for soils to adjust to the new foundation and
|In highly expansive soil areas, slab foundations can be designed for up to
4 inches of soil movement.
landscape irrigation, which is why builders prefer to wait until the end of the typical 1 year workmanship warranty period to make any repairs. Cosmetic repair of common cracks is considered routine, long-term home maintenance. The vast majority of cracks are cosmetic, but
how can you
tell if a crack is a true structural concern? As a general engineer’s guideline, cracks that are hairline up to 1/8 inch in width are considered negligible to slight, 3/16 – 9/16 inch are moderate, 9/16 – 1 inch are severe and over 1 inch are very severe (Forensic Geotechnical and Foundation Engineering, R. W. Day, 2011). Cracks alone are not necessarily indicative of a structural concern.
Cracks are more likely to be a structural concern if accompanied by other indications of structural distress, such as inoperable doors and windows, or excessively sloping floors and surfaces. Cracks with significant vertical displacement across the face of the crack may indicate a structural concern. Cracks in basement walls, especially horizontal cracks, accompanied by bowing or leaning of the wall are cause for concern.
If in doubt about the seriousness of cracks, retain the services of a qualified professional structural engineer, licensed in your state. The engineer will make observations and take photos and measurements. A floor elevation survey may be conducted to evaluate structural deflection (bending) and tilt. The measurements and survey may be used as reference points, if needed, to compare with any future measurements and surveys. The engineer may recommend remedial measures such as drainage improvements, landscape adjustments, rain gutters, foundation watering or foundation repair. The best time to make any cosmetic repairs is when foundation movement has ceased. If the home is covered by a third-party structural warranty, the warranty company has qualified warranty administration personnel available to answer coverage questions over the phone.
-Walt Keaveny, MS, PE, PG.