Drainage

When it comes to moisture around your foundation, you are striving for consistent, moderate moisture; not saturation. Too much moisture is just as bad for your foundation as not enough. Next to a controlled watering program, nothing is more important to a stable foundation than proper drainage.

POSITIVE DRAINAGE
All sides of the house should exhibit positive drainage. Positive drainage means water properly flows away from the house. A recommended slope is 1 inch per foot for a distance of at least 4 feet from the foundation.

NEGATIVE DRAINAGE
Negative drainage means water flows toward the house often resulting in large puddles around the foundation. Pooling water near the foundation can cause a moisture differential around the perimeter of the house. When water is allowed to pool near or against the foundation, 1 of 2 things will occur. The first is that the soil will absorb the moisture causing the soil to expand and this will heave (lift) the foundation causing foundation damage. Conversely, when the soil is saturated and reaches what is called the liquid limit, it can lose its ability to carry a load. This will cause the foundation to sink into the saturated area, like quicksand.

Water, both standing and running, can also dissolve and carry soil which supports the foundation. Wet spots can be caused by negative/neutral drainage, dripping faucets, leaking drains, plumbing leaks, air conditioning condensate drains, etc… The effect is much more pronounced if the surrounding soil is dry.

Provide positive drainage away from the slab perimeter. Any standing water near the foundation slab, current or future, should be eliminated. This will promote even moisture content underneath the slab and cause less movement of the soils beneath the foundation slab.