Condensation
Due to the high humidity level in a dirt crawl space, cool surfaces such as the earth at 55 degrees, concrete and metal surfaces will sweat with water vapor condensing out the air.
Outside Air
Most dirt crawl spaces are vented to get the moisture out. The problem is that the vents let warm humid air in during the summer. This adds moisture to the crawl space, and makes the house harder to air condition as all this moisture needs to be wrung out of the air.
Mold Spores
Mold spores, the seeds of mold, are in the air everywhere. All they need to grow is organic material such as wood, the right temperature range and moisture.
Sealing Outside Air
Vented crawl spaces in warm and cold climates are a bad idea.
