How do you know what’s wrong in a basement just by looking at it? Don’t you need to take stuff apart to figure out the problem?
We’re geniuses. Next question!
Just kidding. We look at a number of physical symptoms that help us diagnose the problem. Many of the symptoms we use will be the same things that caused the homeowner to call a contractor or engineer in the first place.
To risk oversimplifying, a residential foundation’s job is twofold: 1) to keep the home from sinking and 2) to keep soil outside the basement or crawlspace in place. Almost by definition, if a foundation has problems it’s because it’s not doing one of those two jobs. Certain patterns of cracking or distress in the wall and its finishes will almost always indicate the particular type of problem in much the same way that a sick person’s symptoms lead a doctor to a diagnosis without surgery.
1) Sinking – or more accurately settlement – occurs when the soil underneath a portion of the foundation is not strong enough to support the weight of the house. That portion of the foundation settles, and we see doors and windows that don’t operate properly or diagonal cracking in walls as the house racks slightly.
2) Soils outside the basement or crawlspace push in on the foundation wall. A foundation wall works in this case by being restrained at the top and at the bottom as well as being strong enough in the middle not to bend or break. Imagine a book shelf full of books – a thick shelf with good supports works well. A thin shelf bends too far or cracks. A shelf missing a support on either end falls. In a soil pressure failure, we see inward movement of the top of the wall, horizontal cracking in the middle, or sliding out of the bottom depending on the part having trouble. We may see some diagonal cracking at the corners of the wall as stresses distribute themselves around the corner in the wall. We generally don’t see window or door problems because the first floor of the home stays relatively planar.
Occasionally a foundation will exhibit symptoms that are more puzzling, but usually when we see the cracking patterns described above, we can decipher the gross problem without taking walls apart.
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