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Greenville Utilities recommends following the North Carolina Uniform Residential Building Code on the number and placement of crawlspace and placement of crawlspace foundation vents. The E-300 Program favors placing a polyethelene ground cover in the crawl space, which allows the code requirement for the net free ventilation area to be reduced by 50%.

In past years, an industry-wide "set recommendation" was to close foundation vents in the winter to reduce the potential of pipes freezing in the crawl spaces and to leave the vents open at all other times during spring, summer and fall. However, now sufficient evidence suggests that a change in procedure is needed for most homes in our area because TOO MUCH ventilation occurs during our hot and humid summers.

Simply put, during hot and humid weather the warm, moist air migrates into the crawl spaces and through the vents and condenses (turns into water) on metal ductwork, duct insulation, floor joists, floor insulation and curtain walls. This moisture can rust and damage ductwork and contribute to mold, mildew and fungus growth. The moisture also eliminates the insulation value of the duct and floor insulation, and it can contribute to wood rot.

Greenville Utilities recommends not using automatic foundation vents that open only when the outside temperature is warm. A simple solution to this problem is to dry the crawl space with natural air movement in the spring and fall, and LEAVE THE VENTS CLOSED during the hot, humid summers and throughout the winters to prevent the moisture problems mentioned.