I have very high humidity in my house during the winter season. There is electric ceiling heat throughout the house with a crawlspace and vents. there is plastic on the ground. Seems like the heat penitrates the floor because my crawlspace is very warm in the winter, summertime it is cool. During springtime when days are nice we open the windows and within 15 minutes the humidity drops drasticly, but when we close the windows, the humidity level starts to rise. My floor joists are not insulated, just the stringer joists are. Only one spot under the house seems to be wet but there is no plumbing leaks. Problems in the past with water underneath the house, but that was taken care of with slopping the land away from the house and sinking a perferated tile and installing new gutters and downspouts.