This is a 24 gauge panel system, installed up at Alpental, so the snow during winter is DEEP. The weight of the snow actually ripped the panels right off the roof, the screws cutting through the 24 gauge material. Before installing the panels, the Drag load needed to be determined to establish the number of "Drag Screws" to use. Drag Load is the force imposed upon a sloped panel caused by gravity and sliding snow. Standing seam panels, those attached to the roof structure with concealed clips, are free to “float” with expansion and contraction. If left completely free, they would slide off the roof. Drag load has to be combated by “fixing” one end of a standing seam panel. This is typically accomplished under the ridge/peak flashing to conceal the screw. At the “fixed” point, the panel is through fastened to the substrate. The type and number of screws needed, per panel, to resist drag load forces are determined by investigating the substrate material, slope, length of panel, panel width, and geographical snow load. It all comes down to the importance of following the manufacturers recommendations, reading and calculating the load tables, and understanding all of the conditions that might effect the metal roof installation.
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