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Title
Air Intrusion and Its Effect on Moisture Transport in Mechanically Attached Roof Systems
Air Intrusion and Its Effect on Moisture Transport in Mechanically Attached Roof Systems
Date
9/2011
9/2011
Author(s)
Suda Molleti; Bas Baskaran; Peter Kalinger; Pascal Beaulieu
Suda Molleti; Bas Baskaran; Peter Kalinger; Pascal Beaulieu
Page(s)
Keyword(s)
air intrusion; moisture; mechanically attached; wind; dynamic pressure
air intrusion; moisture; mechanically attached; wind; dynamic pressure
Abstract
About one fourth of North American buildings with low-slope roofs (4:12 or less) have mechanically attached roof assemblies, and their popularity continues to grow. In such systems, because of the flexible and elastic nature of the waterproofing membranes and their attachment mechanisms, wind and building mechanical pressurization from the interior causes the membrane to balloon or flutter. The membrane deflection’s volume change causes negative or bubble pressure below the membrane, which is equalized by the indoor conditioned air moving into the assembly, which is termed “air intrusion.” To measure air intrusion in mechanically attached roof systems, the National Research Council of Canada began an experimental study and developed control data as part of the Special Interest Group for Dynamic Evaluation of Roofing Systems (SIGDERS) research. To relate air intrusion to moisture transport in mechanically attached roof systems, a spin-off project began in collaboration with the Canadian Roofing Contractors’ Association (CRCA), NRCA and four major roofing material manufacturers: Carlisle SynTec, Carlisle, Pa.; Dow Roofing Systems, Holyoke, Mass.; Firestone Building Products, Indianapolis; and Sika Sarnafil, Canton, Mass. The paper discusses the research findings from this ongoing study, which addressed the following tasks: • Test additional systems for air intrusion quantification and compare with the SIGDERS control data. • Determine effects of air intrusion on moisture transport in mechanically attached roof systems compared with vapor transmission and establish air intrusion limits for potential condensation in these roof systems.
About one fourth of North American buildings with low-slope roofs (4:12 or less) have mechanically attached roof assemblies, and their popularity continues to grow. In such systems, because of the flexible and elastic nature of the waterproofing membranes and their attachment mechanisms, wind and building mechanical pressurization from the interior causes the membrane to balloon or flutter. The membrane deflection’s volume change causes negative or bubble pressure below the membrane, which is equalized by the indoor conditioned air moving into the assembly, which is termed “air intrusion.” To measure air intrusion in mechanically attached roof systems, the National Research Council of Canada began an experimental study and developed control data as part of the Special Interest Group for Dynamic Evaluation of Roofing Systems (SIGDERS) research. To relate air intrusion to moisture transport in mechanically attached roof systems, a spin-off project began in collaboration with the Canadian Roofing Contractors’ Association (CRCA), NRCA and four major roofing material manufacturers: Carlisle SynTec, Carlisle, Pa.; Dow Roofing Systems, Holyoke, Mass.; Firestone Building Products, Indianapolis; and Sika Sarnafil, Canton, Mass. The paper discusses the research findings from this ongoing study, which addressed the following tasks: • Test additional systems for air intrusion quantification and compare with the SIGDERS control data. • Determine effects of air intrusion on moisture transport in mechanically attached roof systems compared with vapor transmission and establish air intrusion limits for potential condensation in these roof systems.