The moisture content of the soil that supports and surrounds your home’s foundation is critical to its structural integrity. Too much moisture, and that soil can expand, soften or wash away. Too little, and it can dry out and shrink. In this case, we’ll concentrate on reducing problems caused by too much moisture.
As the seasons pass, we experience cycles of wet and dry periods. These affect the soil that surrounds and supports our home. Depending on the type of soil, increased moisture can cause it to expand, putting additional stress on the foundation walls. Excess moisture can also develop hydrostatic pressure in addition to the lateral pressure exerted on the walls by the soil. These pressures can exert several thousand pounds per square foot of additional pressure on your home’s foundation, causing it to crack and eventually fail. During dry periods, soil can shrink and crack, reducing its structural integrity.
When you have a heavy rainfall or a large snow melt, excessive amounts of water enter the soil surrounding your home. In rare cases, the speed and amount of water ingress can actually cause soil to wash away around or under your home, leaving empty space that cannot support the massive weight of your home and its contents. This can lead to part of your home’s foundation cracking and settling as it sinks into these voids.
Ideally, you want water to drain away from your home’s foundation, so it won’t cause the problems mentioned above. You can help ensure this by measuring the drop as your yard slopes away from your foundation. In most cases, you should aim for a five percent grade, or a drop of about six inches for the first 10 feet away from your foundation.
You can measure this drop with a couple of stakes, a ten-foot piece of string and a ruler (a spirit level can be handy too). Simply pound two stakes into the ground, one right by your foundation and the other 10 feet away. Tie one end of the string to the stake by the foundation and make sure it is at ground level. Tie the other to the stake ten feet away. Then make the string run level as it stretches from one stake to the other and measure how far up the second stake it sits. If it’s six inches, you’re good! If it’s less, you may need to add fill dirt around your home’s foundation and tamp it down.