Why is the insulation in my crawlspace falling down? As humidity from the crawlspace evaporates into the insulation, it becomes heavy and begins to fall. The longer the insulation absorbs moisture, the more it tends to fall apart and become less effective.
How does humidity affect the insulation? When fiberglass insulation becomes filled with water from evaporation of standing water, it will temporarily lose a substantial measure of its thermal resistance (R-value). In this case the spaces between the fibers that were previously occupied by air are now occupied by water. Since water is a much better conductor of heat than air, the water presence would cause the insulation to have reduced thermal performance. However, this is only a temporary situation. As soon as the water evaporates and the insulation becomes dry again, it will regain its original performance level.
If the product has been saturated with dirty or contaminated water, Owens Corning recommends that it be replaced. Here is the reasoning: when the water evaporates, deposits of foreign materials that remain may decrease the R-value, and may also give mold and or mildew nourishment and a place to propagate. This growth, and/or odor, may then also be transferred to other building materials.
Since crawl space dampness always moves toward the drier upstairs areas, higher humidity will result in costlier heating and air conditioning bills. When the underflooring insulation collects moisture, or sags from excessive wetness, the heating and air conditioning costs are driven even higher.
What can I do to fix the problem? The only way to remedy the situation is to control the humidity in your crawlspace area.
This information was taken from the Owens-Corning Web site: http://www.owenscorningblog.com/blog/mt-tb.cgi/144