Influence of wind-tightness quality at the wall-roof intersection on the heat flow through lightweight roof constructions

Abstract

For a reduction of heat energy losses much effort has been undertaken during the last years to improve insulation, heating and ventilation systems. Despite, wind-tightness is often disregarded, even though the importance of heat losses through wind-washing has already been shown by research findings. Especially the realization of the wind-tightness at the intersection of wall and rafters proves to be challenging due to difficult geometrics at this position. The presented study clarifies the influence of different wind-tightness qualities at the wall-roof intersection on the heat flow through a rafter roof. For that purpose laboratory tests were carried out. The gained data shows that the insulation material has a very strong effect on the increased heat flow through the roof caused by wind-washing. The results also point out that a certain duration and value of the pressure difference (wind load) between eaves and attic is necessary to cause an effect. The influence of the pressure difference is more pronounced compared to the influence of the gap geometry at the wall-roof intersections. While the projecting roof and the fixation of the roof underlay have a very strong effect, the inclination of the roof has no significant influence on the additional heat flow due to low wind-tightness.