Aerodynamic and water penetration investigations upon pitched roof vents

Pitched roof vents (PRVs) can be used both to extract air into the atmosphere (‘blowing’) and to draw in fresh air (‘sucking’). In both of these situations, the PRV facilitates the exchange of air between the inside and outside of a building. Photographs of typical generic PRV designs are presented. As shown in these photographs, PRVs are mounted within a pitched roof, and may or may not protrude slightly above the roof surface. Hence their performance is likely to be influenced strongly by wind flowing above and around the roof. The internal and external design of PRVs is complex, and PRVs are designed to strike a balance between aerodynamic efficiency, weather-tightness performance, and cost of manufacture. ments have been undertaken at Building Research Establishment (BRE) to test the weather-tightness and aerodynamic performance of PRVs. This paper describes the test rig and the methods used to obtain experimental results. A particular feature of this test rig is that it is able to discriminate between leakage through the PRV, the roof covering, and the interface between the roof covering and the PRV. range of UK domestic and industrial marketplace PRV products were tested. For the aerodynamic performance tests, typical results are presented for different wind speeds and different roof pitch angles. An empirical equation is presented that was found to describe well the aerodynamic performance of every PRV tested. For the weather-tightness tests, a new visual criteria is suggested which, although subjective in nature, provides very useful information about water penetration that cannot be obtained in any other way. A typical weather-tightness plot is presented that uses the new visual criteria, together with the more traditional method of weighing the water ingress. For both the aerodynamic and weather-tightness tests, the findings and conclusions of the overall test programme are presented.