Loose-Fill Fiberglass R-Value vs Temperature.

Loose-Fill Fiberglass R-Value vs Temperature

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 (–20°F / –35°C), 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 –18°F (–28°C), 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)

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