Since the crawl space is generally not very inviting space, a lot of people never go down there. It is not until a homeowner has strong musty odors coming up and through the home that they become concerned. A lot of times this odor is caused by mold and bacteria growth. If not treated correctly, crawl spaces are generally a damp, humid environment. This moisture will rise up into the wood above, and over long periods of time will cause mold and bacteria to grow. Although Colorado generally does not have a high humidity level, all soils hold moisture and in poorly ventilated and enclosed environment such as a crawl space, humidity levels can rise quickly. If large amounts of water from heavy rains or plumbing leaks are ever introduced into the equation, mold will likely begin to grow.