What may appear to be an obvious solution to this problem leads to another misconception that is all too common in the construction industry today. Unfortunately many of the common insulating materials used today do a poor job of stopping air movement. Loose blown fiberglass and batt insulation can effectively slow conductive heat loss, but are susceptible to air moving around and through them. Compounding the problem, laboratory testing has revealed that air moving through fiberglass can degrade the insulation's performance to well below its rated R-value. Building scientists and researchers have concluded that adding insulation is not enough.
Insulation only works when it is installed in an air tight configuration.
Another common problem is outside air infiltrating ceiling cavities between heated floors via the eave. This is most evident in homes with one story and a half. As is shown here, this kneewall floor and wall are insulated. However outside air can easily bypass at the critical juncture and penetrate the heated cavity beyond. One frustrated homeowner had just moved into her newly built home when the bathroom plumbing, which was located next to a kneewall, froze.