Experimental results obtained by guarded hot box testing of low density loose-fill insulations have been analyzed using convective models. Closed and open specimens have been studied in an attic configuration with heat flow up. Experiments were conducted with and without a transverse air flow across the top of the specimens. The occurrence of convective movements inside the insulation was investigated for different applied thermal gradients and air permeabilities of insulation. Comparisons between theoretical and experimental results are presented and discussed.

The study has shown that the boundary conditions at the open top surface of an attic insulation are the driving force in determining thermal performance. Both the model and the experiments have shown that a significant reduction in thermal performance for presently used glass fiber insulations can only occur under severe climatic conditions (i.e., where a temperature difference greater than 40°C will be present).