Local loss coefficients inside air cavity of ventilated pitched roofs

Abstract

Pitched roofs with a ventilated air cavity to avoid snow melt and ensure dry conditions beneath the roofing are a widely used construction in northern parts of Europe and America. The purpose of this study has been to determine pressure losses at the inlet (eaves) and inside the air cavity consisting of friction losses and passing of tile battens. These results are necessary to increase the accuracy of ventilation calculations of pitched roofs. Laboratory measurements, numerical analysis as well as calculations by use of empirical expressions have been used in the study. A large difference in the local loss coefficients depending on the edge design and height of the tile batten was found. The local loss coefficients of the round-edged tile battens were approximately 40% lower than the local loss coefficients of the sharp-edged tile battens. Furthermore, the local loss factor increased by increasing height of the tile batten. The numerical analysis was found to reliably reproduce the results from the measurements.