Convection and radiation in layers of low-density fibrous insulants

Attempts to reduce national energy demands have led to increases in insulation thicknesses in roof spaces in northern Europe and North America. Generally it has been assumed that the apparent thermal conductivity of each material used has been a constant and equal to the value obtained in a testing laboratory under different conditions. Examination of the vertical temperature profiles through various horizontal thicknesses of loose-fill mineral wool insulants suggests that convection in the upper surface layers exposed to the free air and radiation contributions result in much larger apparent thermal conductivities than those quoted in the literature and the magnitudes of these effects increase with the thickness of the insulant layer.