Foundation drainage problems, excess water, and flooding.

Water is a powerful and persistent force. It will erode gullies into valleys, and often causes landslides, mudflows, and floods. Water is responsible for the Grand Canyon – and frequently for foundation problems. As an interested observer of foundations in distress over the past five decades, I find that most foundations and hillside problems are either caused or aggravated by water.

Some dry clay soil particles can expand twenty or more diameters when they become wet. On a sloping site, a unit of clay will expand downhill as gravity inhibits uphill expansion, as shown in the example above. When the same unit of soil dries, it contracts in the downhill direction, because gravity inhibits uphill contraction. The net result then, is a downhill creep.

Too much water makes mud. We know mud has less bearing capacity than dryer soil. We walk on average soil without sinking. On mud our weight displaces the soil and we sink. We should expect a similar experience with the footer of a foundation accompanied by standing water saturating the perimeter soil.

DESIGN AND BEHAVIOR

Now consider the wind-force gathering, or sail profile effect on the roof and the sides of a house. The forces from the wind buffet the roof and get transferred vertically through the framing members and help pound an already deficient bearing medium downward. Consider only 1/10 of an inch per season. In ten years, one might expect one inch of differential settlement at the perimeter.