Numerical Studies of Air Flow by Natural Convection in Ventilated Insulated Slanting Roofs

A common roof design in the Scandinavian countries is the ventilated slanting roof. Ventilation of the roof has two purposes; to transport any moisture that has penetrated the roof construction out of the roof and to keep the outer roof surface cold enough to avoid snow melting. Snow melting on the roof's outer surface can cause pools of water freezing near the eave construction, which again can cause mechanical degradation and leakage. There have been some discussions regarding how large the air gap in ventilated roofs should be in order to provide sufficient ventilation for ensuring low temperatures and for allowing transport of moisture out of the roof. This paper presents temperature distribution, stream contours and mass flow rates found from 2D CFD simulations of natural convection is some typical roof configurations in Norway. The flow rates are reported for two sizes for the roofing battens, two different roof angles, and roof size. External wind effects are not included in these studies. The results may be used as input in heat and moisture simulation tools, where ventilated roof constructions are investigated.