Effect of Fastener-Deck Strength on the Wind-Uplift Performance of Mechanically Attached Roofing Assemblies

A roofing system consists of a waterproof membrane, attachments, cover board (if present), insulation, and vapor or air barrier [retarder (if present)]. A roof assembly is a roof system that includes the structural deck. Wind-uplift ratings are reported by subjecting roof assembly mockups to wind dynamics. Most of the time, technical reports clearly document the properties of membranes and attachment systems (fasteners, plates, and seams) and only briefly mention the strength of the fastener-deck interface. Research by a North American roofing consortium established at the National Research Council of Canada, the Special Interest Group for Dynamic Evaluation of Roofing Systems, has demonstrated the significant influence of fastener-deck parameters on the wind-uplift resistance of mechanically attached roofs. This paper presents data and information from this ongoing investigation. Seven different roofing assemblies using three widely used roofing membranes with different fastener-deck combinations were constructed and tested under dynamic wind conditions. Assembly responses were measured based on two design factors: pressure and force. The present study identified three parameters characterizing the fastener-deck interface strength: deck grade, deck gauge, and fastener type. The study found that assemblies tested with steel decks having thicker gauge or higher yield strength tend to have greater fastener-deck strength and therefore they sustain higher wind-uplift pressures compared to assemblies with thinner gauge or lower yield-strength decks. Similarly, assemblies where the membrane attachment is made with fasteners with larger shank diameters sustained higher wind-uplift pressures compared to assemblies installed with smaller shank diameter fasteners. This study also found that fastener pullout resistance could be used as a verification factor for estimating assembly wind resistance.