Figure 2.4 — There is a problem with loose-fill fiberglass attic insulation in cold climates. It appears that , as attic temperature drops below a certain point, air begins to circulate into and within the insulation, forming “convective loops” that increase heat loss and decrease the effective R-value. At very cold temperatures (-20F), the R-value may decrease by up to 50%.
In full-scale attic tests at Oak Ridge National Laboratory, the R-value of 6 inches of cubed loose-fill attic insulation progressively fell as the attic air temperature dropped. At -18F, the R-value measured only r=9. The problem seems to occur with any low-densitiy, loose-fill fibrous insulation. (J.D. Ned Nisson, “Attic Insulation Problems in Cold Climates,” Energy Design Update, March 1992, 42-43)