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Home >> Articles >> Ugly basement walls: How bad is bad?
 From The Best Times - May 2005By Don Carter, Structural Engineer Let’s agree on this. There are no perfect houses. Even a new house has flaws if you look for them. You and I live in a part of the world where clay soils are prominent. Since clay shrinks and swells with changes in moisture, most houses move - and movement produces damage. My company examines houses every day, but we don't look for perfection. Instead we benchmark against the following guidelines: • Straight basement wall cracks. Cracks less than .064 inches wide typically don't leak. If you run your finger over a crack and it doesn't have a big offset, it can generally be left alone. • Cracks wider at the top than the bottom indicate settlement. We use a laser level to define elevations around the basement perimeter and down the center beam to locate low spots. Change-in-elevation limits vary, depending on which code you consult, but we use 1 inch for every 20 feet. Most houses, even unsightly ones, are within this limit. • Dark spots adjacent to the floor probably indicate standing water outside the wall. Houses are built with a collector pipe to eliminate water, but after about 20 years, those pipes become plugged and water no longer has an escape route. While the dark spot itself does not represent damage, it is a harbinger of future damage from water pressure. • A leaning wall is a problem that may be caused by water pressure. The long wall's top gets pushed in, and because intersecting side walls won't give, the leaning wall splits diagonally near its corners. There is a formula to compute how much a wall can lean before it becomes unstable, but for simplicity, figure that a lean greater than 2 inches needs corrective action. • "Wall sweep" is often seen in the long front and back walls of ranch-style homes, appearing as inward arching. Wall sweep is time-dependent and grows with age as concrete undergoes a phenomenon known as "creep." This problem can often be left untreated, unless you see daylight between the wall top and wood plate. • Basement floor cracks are nearly universal and typically don't need fixing. Conscientious builders put control joints (saw cuts) in basement floors to minimize this problem. The floor still cracks, but you don't see it as much. If your basement walls are made of masonry block, you have a different set of standards. Significantly bowed or split block walls should be evaluated by a design professional. Whether in concrete or block, we advise clients to monitor cracks for ongoing change. If a wall is moving, it is unstable and needs correction regardless of whether it meets the above limits. Devices exist to monitor movement, but often a single swipe of spackle across a wall crack will show whether there is movement. If the spackle breaks apart, the wall is moving and it's time to call for help. Don Carter is a licensed structural engineer and managing general partner of Foundation Engineering Specialists LLC, a company specializing in residential design and assessments.  |
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