. Properly ventilating the basement will help keep the humidity down, and insulating the main floor will prevent moisture intrusion into the house and heat loss into the basement.
--Welmoed Sisson
(Maryland Home Inspector)
WOW, just wow.
I built new homes for a living and work in a textbook area when it comes to difficult moisture, and mold issues in basements and crawl spaces. I generally build sealed, conditioned crawl spaces. Just a few things that I have learned using everything from building inspector input, published research, personal trial and error, and observing countless sucesses and failures in local post war construction.
First and foremost, ventilating a basement in many (most) climates WILL NOT keep humidity down. In many mixed climates it will greatly increase humidity and do serious damage to the structure and the health of the occupants. It's basic common sense. The exterior air being exchanged needs to be dry <50% M.C. driven by wind pressure at an adequate rate of exchange, and of a suitable temperature that it neither heats or cools the interior space at undesirable levels. Fact is that this magical set of conditions doesn't happen too often. Ventitation in cold conditions can be both an expensive waste, as the heating system works to compensate for the loss, and a disaster if pipes freeze. In hot, humid summer conditions, full ventilation leads to serious moisture and mold issues as the wet, hot air condenses on cool interior walls and causes the interior moisture level to spike.
Second, using the homes HVAC system to control basement or crawl space conditioned can lead to serious health issues. If conditions deteriorate in the below grade area, ( ie, moisture levels climb, and mold growth proliferates) and it isn't noticed or controlled by the occupants, the HVAC system will distribute mold throughout the home. I HAVE had it happen.
Third, insulation DOES NOT control moisture, it isn't designed to do so, and it shouldn't. If you are refering to the practice of installing kraft faced fiberglass with the "vapor barrier" toward the warm side (up in this case) in the false belief that it is somehow preventing vapor transfer, well good luck with that. In a basement where moisture issues are properly addressed, floor insulation can be beneficial. In a wet basement or crawlspace, floor insulation, particularly fiberglass batting, can be an absolute disaster. IF the O.P were to follow your advice to install a vapor barrier, then insulation, under his floor joists and maintain the space as vented, he will end up with a mess. I have seen a case when the floor joists were rotted, full of carpenter ants and the floor was collapsing into the crawl space because it was fully vented with the vapor barrier and insulation installed per your recommendations. Given the hot humid conditions in TN, I would seal the space tightly, get a dehumidfier cranking 24/7 and not worry about insulating, or installing a vapor barrier anywhere. Naturally the underlying issues of grading, gutters, etc need to be addressed, asap. As for the "wet when rains" issue, you may be in a situation where it will be impractical, or too expensive, to really eliminate the issue entirely. Especially if the issue is a water table that rises temporarily. Thoroseal brand masonary waterproofing done with their acrylic additive can give some amazing results when used on the interior of the block wall. Good luck