How Bad Is Bad?
By: Don Carter, MS, P.E.
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 and since clay shrinks and swells with moisture change, 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” wide typically don't leak. If you run your finger over that crack and it doesn't have a big offset, it can generally be left alone.
- Cracks Wider At The Top Than 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” every 20'. Most houses, even the 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 there to eliminate water but after about 20 years these pipes get 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.
- Leaning Wall - This is one problem water pressure can cause. The long wall's top gets pushed in and since 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 anything greater than 2” needs corrective action.
- Wall Sweep - Found in ranch style homes, sweep is often seen in the long front and back walls as inward arching. It's time dependent and grows with age as concrete undergoes a phenomenon known as creep. This problem can often be left as is 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, you just don't see it as much.
If your basement walls are masonry block you have a different set of standards. Significantly bowed or split block walls should be evaluated by a design professional. Be it concrete or block, we advise clients to monitor cracks for ongoing change. If the wall is moving, it is unstable and needs corrective action regardless of whether it meets the above limits. There are devices 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.