This study documented that houses in the southeastern United States built on typical wall-vented crawl spaces possess the following characteristics: 1) bulk water, water vapor and associated moisture issues, 2) mold spores, 3) measured holes between the crawl space and living space and 4) measured transmission of mold spores from the crawl space to the living space. When these characteristics exist together, the study indicates that contaminants (mold spores and moisture vapor) present in the crawl space are being transmitted through holes in the house floor and heating, ventilation and air conditioning (HVAC) system into the livable parts of the home, thereby exposing occupants to potentially harmful crawl space contaminants. These results confirm vented crawl spaces as important sources of mold species in the home environment. In order to reduce this exposure, closed crawl spaces in combination with thorough house and duct air sealing are recommended. Such a system was found to be a robust intervention that reduced the moisture and indoor air quality problems associated with typical wall-vented crawl spaces.