Proper lot grading is an important consideration when dealing with wet basements. No foundation wall system is completely waterproof. Water accumulating in the soil outside the building will usually leak through eventually. The secret is to keep the soil outside the building dry. If the ground around the building slopes so that surface water runs away from the building, soil close to the foundation is dry and the basement is far less likely to leak.
Common Problems with Lot Grading
WET BASEMENTS The theory is simple. If there is no water in the soil on the outside of the foundation wall, no water will get into the interior. Most wet basement problems can be eliminated or dramatically reduced with good grading and proper performance of gutters and downspouts. The ground around the home should slope down six inches for the first ten feet away from the home. This can often be done by adding topsoil (not sand or gravel).
Where the general topography directs water towards the house, further measures are sometimes required. A swale (a shallow ditch with gently sloped sides) may have to be constructed to divert water run off around the house to areas that are lower-lying.
If the general topography of the neighborhood is such that the house lies in the lowest area, grading improvements may improve the situation; however, further measures may be necessary. See Section 10 of the Interior chapter for more information on wet basement problems.