Limitations

Laboratory attic tests have shown that light-density loose-fill prod­ucts may suffer a reduction as attic temperatures drop further. For example, the actual R-value of loose-fill fiberglass insulation has been shown to decrease by 20 to 40 percent under extreme winter conditions. Oak Ridge National Laboratory measured R-values as low as R-12 at an attic temperature of 9°F for an R-19 fiberglass installation. Follow-up testing at the same laboratory seems to sug­gest that convection currents actually resulted in an increase of only $20 in energy cost (gas heating bills) per annum. Electric resistance heat costs were slightly higher.10