Crawl Space Moisture Problems


Most crawl spaces will eventually experience moisture problems due to heavy rain, high humidity or leaking plumbing. Left unchecked, these sources of moisture can cause mold and damage the home's wood frame. Identify the problem and take steps to prevent it from reoccurring.


  • Check underside plumbing for signs of prolonged leakage. Look for soil under pipes that is consistently wet, or small bands of fungus growing under the pipes. Look for cracks or holes in the foundation walls--water can work its way into the smallest areas. Insects can also find their way into the damp openings and set up breeding grounds. Wet soil and insect fecal matter can provide a home for mold. Mice and rats may soon follow and invade the upper floors.

Clean Up

  • Remove items from under the home, including fallen insulation or stored material. Stacked boxes can create hiding places for insects and impede air flow crucial for ventilation. Proper ventilation will aid in removing moisture. Install crawl-space air vents and seal the ground with a layer of thick plastic sheeting--the plastic will stop ground moisture from rising during heavy rains. Repair all foundation cracks and holes. Check to ensure that ground water is not flowing under the home; this may entail the installation of drainage ditches. Properly insulate all flooring that is exposed to the crawl space--temperature differences can cause condensation. Condensation can then build up on floor joists and the flooring itself.

Fans and Dehumidifiers

  • Homeowners living in areas with high humidity may need to install a ventilation fan or a dehumidifier. Ventilation fans, properly oriented with metal screened vents, can be controlled by a humidistat. The humidistat will operate the fan when the crawl space's humidity rises to a certain level. Air can be drawn across the space through the metal vents and pushed out by the fan. Dehumidifiers are used when the area is constantly damp and no ventilation can be installed. In these cases, the dehumidifier is connected again to a humidistat. The controller switches the unit on and off when needed. A drainage hose is connected to the collection tank so the water can be piped a distance from the home. A strict schedule of maintenance needs to be performed to keep the unit clean.

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