How to Ventilate a Crawl Space

Add vents to your foundation. If there are no vents in the foundation of your house, it's difficult for air to circulate properly. This lets moisture build up in the crawl space, causing mold growth and affecting the interior climate of the house. How you add a vent depends on the construction of your foundation. In most cases foundations are constructed of cinder block. With a sledgehammer and chisel, knock out part or all of one of the cinder blocks and put a screen in its place. Special sliding vent doors can also be installed--these have the added advantage of letting you regulate the temperature of the crawl space to some extent.

Add a crawl space fan. As before, you need to make a hole in the foundation, unless there already is one. Crawl space fans are readily available through commercial sources, and require a 110-volt electrical source for operation. When installing or selecting a fan, choose between setting it up to operate on a simple switch, or have it triggered to come on automatically when the humidity in the crawl space reaches a certain level. The latter is preferable, as it automatically monitors the status of the crawl space's humidity. Follow manufacturer's instructions when installing a crawl space fan.

Install a crawl space dehumidifier. This is an expensive option that's best undertaken only in cases of extreme crawl space dampness. While you're not, strictly speaking, ventilating the crawl space, a dehumidifier can solve the problem of moisture buildup very effectively. You need a power source for the dehumidifier of course--follow instructions for installation and mounting.

Install a vapor barrier in your crawl space. Again, this is not, strictly speaking, ventilating the crawl space, but a vapor barrier of impervious fabric stops the inflow of moisture and condensation that can result in a damp crawl space. Contact a local contractor or building supplies store for information on available materials, installation and cost.