Moisture management typically involves several solutions working together. Adding plastic sheathing over the soil as a crawl space vapor barrier is a good start. Also check your outside drainage conditions. Gutters must be clean, free-flowing and discharging four to six feet from the foundation. Grading also has to slope away. (See our article on wet basement and crawl space tips.)If the crawlspace moisture problem is severe, another step might be to install a crawl space foundation vent fan, wired into a humidistat. The fan can be set to kick on whenever humidity gets high enough and pull drier outside air through the space to minimize condensation on the floor joists and the potential rot, mold and insect problems that could ensue.