NEWS for North Dakotans
Agriculture Communication, North Dakota State
University
7 Morrill Hall, Fargo, ND 58105-5665
June 18, 1998
With summer rain and humidity, damp basements become a common home malady. The cure is a roof-to-foundation approach to keeping moisture at bay, according to Kenneth Hellevang, agricultural and biosystems engineer with the North Dakota State University Extension Service.
One common contributing factor is ventilationadding warm outside air to cool basements can create high humidity and contribute to moisture problems, Hellevang says. That's because the relative moisture-holding capacity of air increases as the temperature increaseswarm air holds more moisture than cold air. When outside air at 75 degrees and 60 percent relative humidity is introduced and cooled to a 65 degree basement temperature, the relative humidity will increase to 85 percent.
"It may seem like a good idea to ventilate your basement to relieve humidity problems," Hellevang notes, "but basements should be isolated from outside air when the basement temperature is cooler than the outside temperature."
Remove moisture from the basement by using a dehumidifier or by running air conditioning, he recommends. Basement humidity levels should be kept below 70 percent to limit mold growth because mold can irritate the respiratory tract and causes damage to materials.
Hellevang urges homeowners to look outside to prevent moisture problems inside. Proper drainage around the home can solve or prevent many basement moisture problems. And saturated soil not only causes water problems in the basement, but also increases the soil pressure on the basement wall, which can lead to structural problems, he cautions.
Many problems can be corrected by controlling water above the ground. One inch of rain on 1,000 square feet of roof amounts to about 625 gallons of water. Getting that water away from the basement is critical, Hellevang says.
"All eave trough downspouts should have extensions to carry water several feet from the house," Hellevang says. "The ground should be sloped to carry the water away from the downspout discharge. Also, the ground should be sloped about one inch per foot near the wall." In some cases it is desirable to place an impermeable material under the soil next to the wall to ensure that the water flows away from the house.
A properly installed drainage system at the house foundation and under the basement floor will ensure a dry basement and eliminate saturated soil conditions next to the wall. A study of leakage problems showed that more than 90 percent were because drainage systems were not installed properly, Hellevang notes.
A properly installed foundation drainage system includes a drainpipe placed alongside the footing with the top of the drainpipe below the top of the footing. An underfloor drainage system should consist of a minimum of 4 inches of gravel under the floor with the gravel layer sloped to the depth of the footing. A drainpipe should be placed on the inside of the footing at the same depth as the drainpipe on the outside of the footing.
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Source: Ken Hellevang (701) 231-7243
Editor: Tom Jirik (701) 231-9629