Uncovered crawl space vents have been linked to many different problems, most of which stem from the dampness that takes root as a result of this exposure. The most common are:
Mold Formation
Mold and mildew quickly take root in damp environments, and your crawl space can offer the perfect conditions. While mold in your crawl space may not seem like a huge issue, it can be; some forms of mold are toxic, while others attract pests such as cockroaches. All in all, mold in your crawl space is to be avoided.
Cracked Walls
Dampness in your crawl space can cause and compound structural damage as the water repeatedly freezes and thaws during sudden cold snaps and thaws. As these cracks widen, they will let more water in and gradually undermine the structural stability of your property.
Uneven Flooring
Damp and rotting joists and supports can quickly begin to sag. When this happens, you will notice gaps between your walls and floor or a slight tilt to your flooring.