I have a major moisture problem with a home that is one block from Lake Michigan in South Haven, MI. I have a working sump pump below ground level and am still having rotting problems with the floor joists. A local contractor wants to staple plastic to the joists or lay it on the ground. Would you recommend either of these as a solution?
Moisture management typically involves several solutions working together. Adding plastic sheathing over the soil as a crawlspace vapor barrier is a good start. Also check your outside drainage conditions. Gutters must be clean, free-flowing and discharging 4 to 6 feet from the foundation. Grading has to also slope away. See more wet basement and crawlspace tips here.
If the moisture problem is severe, another step might be to install a crawlspace 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 hoists and potential rot/mold/insect problems that could ensue.