In many parts of the country, the basement or lower level might be damp during portions of the late spring and summer. Dampness in a basement is a normal phenomenon that occurs because cool air cannot hold as much moisture as warm air. It does not necessarily indicate that the basement has a water problem. The temperature of the air in the basement or crawl space during the late spring and summer is always cooler than the outside air. Consequently, when outside air infiltrates into the basement through open windows, doors, cracks, or joints, the temperature of that air drops. This cooler air cannot hold as much moisture and results in a higher relative humidity of the air that entered the basement. Depending on the temperature and the amount of moisture present in the air, some moisture might condense on cool surfaces such as foundations walls and cold-water pipes.
Sometimes water droplets on the foundation wall caused by condensation are erroneously diagnosed as caused by seepage through the wall. If you see a damp-wet foundation wall, you can easily check whether the condition is caused by seepage or condensation. Simply fasten a small piece (4 by 8 inches) of aluminum foil to the foundation wall. Using wide strips of an adhesive tape, seal all the edges of the foil to the wall. After the foil has been on the wall for at least twenty-four hours, examine its surface. If it is moist, the condition is caused by condensation. However, if the foil surface is dry and the area behind the foil is damp, the condition is caused by moisture seeping through the foundation wall from the outside. Of course, it is possible for both the foil and the wall to be damp, indicating both seepage and condensation.
Dampness in a basement or crawl space should be controlled. It can produce conditions conducive to the growth of mold and decay fungi. Dampness can often be detected by musty odors or a clammy, close feeling. In the drier portions of the country, normal dampness (not caused by seepage) in the basement can be controlled by opening the windows and ventilating the area. However, in areas where the climate is hot and humid during the summer, the benefit gained by ventilating the area is lost by the introduction of moist air into the basement. In these areas, the dampness in the lower level can be controlled with one or more electric dehumidifiers. Most of these units have a humidity control that automatically shuts the dehumidifier off when the moisture content in the air reaches a preset level. Depending on the weather and the size of the dehumidifier, the unit might have to run for many hours during each day in order to wring out sufficient moisture from the air so that it is not uncomfortably damp.
Water seepage- causes and control
Depending on the topography, drainage conditions of the soil, and groundwater level (water table), the basement or crawl space might be vulnerable to water seepage. Water seepage, as used herein, is a general term that refers to water intrusion into the lower level of the structure. It might manifest itself as a small wet area, a puddle, or layer of water completely covering the floor. If the ground under and around the house is wet, water can seep into the basement through cracks and open joints in the foundation walls or floor slab. Since water seepage can be caused by a number of factors and water can leak into the basement at any number of locations, it is important to determine the cause and source of the seepage so that the proper corrective action can be taken.
For example, if water is entering the basement through the foundation walls, installing a sump pit and pump below the floor slab will not correct the problem. Similarly, if water is seeping into the basement through the floor slab, sealing the walls will not correct the water-infiltration problem. All too often the unsuspecting homeowner is talked into a full waterproofing job, which can cost several thousand dollars, when all that might be needed is to redirect the water discharging from the roof drainage system (gutters and downspouts) so that the water does not accumulate around the foundation.