The purpose of this study was to investigate how natural convection in air-permeable glass wool insulation affects the thermal transmittance in walls, roofs and floor structures. The results can be used to evaluate the need for a convection barrier in thick mineral wool layers. Natural convection is affected by several parameters. In this study, the angle of inclination, the heat flow direction and the temperature difference across the test section have been studied. Thermal transmittance and temperature distribution measured using thermocouples placed inside the insulation cavity clearly showed convection in the insulation when the test section was in pitched roof and wall positions. An efficient measure to reduce the natural convection is to divide the insulation layer into two thinner layers using a diffusion open convection barrier. A convection barrier is recommended by the authors both in wall and pitched roof structures if the insulation thickness exceeds 200 mm.
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