I have found an issue lately in several of the houses I have inspected. The moisture readings in the crawl spaces has been very high. Everytime I have found this issue I have also found numerous vents for thee crawl spaces closed. When i mention this to the listing agent or buyers agent they tell me the vents were closed for the winter months to keep utility bills down.
Please everyone understand, most floors have insulation in them now closing the vents does not really help with heat loss or lower utility bills that much. What it does do however is create a moisture issue in the crawl space. The humidity in this area elevates and that in turn helps promote microbial growth. The vents are there to promote even and proper air circulation in the cral space. Closing these vents can possibly lead to mold growth on the wood in a crawl space and this is not only bad for the wood but invites insects and MOLD growth which then may become an environmetal health hazzard.
Crawl spaces should be vented to the outdoors to permit water vapor to escape. If the vents are located near each corner, the vents will permit good air movement through the crawl space. A standard metal foundation vent is eight inches by 16 inches and is usually located in the top eight inches of the foundation. It has a metal grid of one-inch squares, may have screen wire to elude mice, etc. and may have an operating metal shutter. See Figure 9. One standard suggestion for vent sizing is one square inch of unobstructed ventilating area for each square foot of crawl space area. Thus, each standard eight inch by 16 inch vent has about 60 to 75 square feet of unobstructed area and is adequate to ventilate about 75 feet of crawl space area. The function of the foundation ventilator is to dissipate the moisture vapor in the crawl space, therefore the ventilator should remain open year round except during the coldest few days.
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