The Causes of Wet, Damp, Crawl Spaces
Groundwater Seepage
Crawl space foundations are built into shallow holes dug out of primarily clay soils creating “clay bowls”. These “clay bowls” hold water much like a pond holds water. Even after the foundation is back filled, this bowl that the basement was built in will still hold water, because the back filled soil is much less dense than the untouched soil around it. Water percolates through the soil and saturates the area in the bowl, and around the foundation. The result: a wet basement and/or crawlspace.
To prevent water from building around the foundation and getting into the crawl space, the builder installs a drainage system around the perimeter at the base, and seals the walls before back filling. However, sometime after construction, the water brings dissolved soil and sediment into the original drainage system and the drainage system begins to clog. Once this clogging process occurs, water builds around the foundation and hydrostatic pressure is created, forcing the water into the crawl space through weak points where the wall and floor meet, as well as through cracks in the walls and floor.
Many crawl spaces have dirt floors. If water is building around the foundation, a dirt floor makes it even easier for water to move in. Muddy crawl space dirt floors easily allow excess moisture to move upwards into the floor joists, flooring, and insulation above.
Vapor Transmission and Condensation in a Crawl Space
Other forms of moisture penetration are much more difficult to see. Vapor Transmission is a process where water molecules move through masonry foundations from the exterior to the interior even in areas where air cannot penetrate!
Also, warm, humid air moves into cooler crawl space environments in the summer. This warm air cools and shrinks. As this happens, the relative humidity rises, and water condenses onto cooler surfaces like cold water pipes, cold air returns, and foundation walls and floors. In the winter, warm air in the basement can condense onto cooler basement walls and floors.
The moisture from groundwater seepage and saturated air is evaporated into the crawl space environment. Once the amount of moisture entering the crawl space exceeds the its ability to evaporate it, signs of moisture begin to accumulate on the walls and floor. Visit our Education Center for more details.
Crawl Space Ventilation
Most crawl spaces contain vents that were installed to allow air to circulate in and out of the crawl space. The unforeseen problem is that it is not always a good idea to circulate air in and out of the crawl space. Warm, humid air in the summer can create high humidity in the crawl space environment increasing the relative humidity. As the warm, moist air cools once inside the cooler crawl environment, condensation can occur. That moist air is absorbed by the wood and insulation above, creating conditions for basement mold growth and structural concerns.
