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Crawl space ventilation is something that every homeowner with a crawl space probably worries about. With the creation of energy-efficient homes that are better sealed off from the environment, crawl space ventilation has become an issue more than ever. A damp crawl space can cause damage to structural components of a house or cause wood flooring to warp, and can also provide an environment for potentially dangerous mold to grow. Installing vents, if there aren't any, or maintaining them, if they already exist, is usually the first step to maintaining correct crawl space ventilation. A good vapor barrier can also help a lot, and modern vapor barriers may eliminate much of the need for ventilation.
Many homes with crawl spaces already have vents, though those without them will often benefit from an installation. It is important that these vents remain unobstructed and undamaged, so that air is able to circulate through them. Some such vents can be closed, though this function should typically be ignored in warm climates. If a home is located in a cold climate, it is sometimes considered safe to close the vents during the winter, to keep the house warmer, though homes in warmer climates can simply leave the vents open all year long. Automatic vents are also typically available, which open and close according to the ambient temperature.
In addition to unobstructed vents and and an unbroken vapor barrier, a few other things can be done for excessively damp or humid crawl spaces. If a crawl space has a history of actually flooding, a pump may be installed to remove excess water. A fan can also be used to increase air flow and dry things out. If the crawl space is excessively humid and normal crawl space ventilation isn't working, a dehumidifier may be the answer. These devices are designed to actually dry out the air in the space.
In some cases, the need for crawl space ventilation can be obviated by a modern vapor barrier and the introduction of heat to the area. This situation is typically referred to as tempered, and can avoid the typically damp or humid conditions often associated with these areas of a home. A crawl space constructed in this way may not only not need vents, but may also allow the homeowner to use the area for extra storage. Since the space is slightly heated and is not damp, it can potentially provide a much safer storage solution than a traditional crawl space.