Mold growing on wood joists can contribute to wood rot. It also has a significant impact on indoor air quality. Approximately 50% of the air you breathe in your home comes from your crawl space. With mold/mildew in the crawl space, this means pollutants are getting into the air you breathe inside your home. You may also notice symptoms such as mildew or musty odors in your home, or high humidity in the home.