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47.5 MB - The Whole Building Design Guide

47.5 MB - The Whole Building Design Guide

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m For structural metal roofs, it is recommendedthat a roof deck be specified,rather than attaching the panels directly topurlins as is commonly done with pre-engineeredmetal buildings. If panels blow offbuildings without roof decking, as shownin Figure 3-17, wind-borne debris and rainare free to enter the building.Roofs over rooms used to store importantrecords (such as police station evidencerooms) should incorporate secondarymembranes to avoid water leakage damage.To preclude water infiltration damage fromexterior walls, avoid locating importantstorage rooms adjacent to exterior walls.Structural standing seam metal roof panels with concealedclips and mechanically seamed ribs spaced at 12 inches oncenter are recommended. If the panels are installed over aconcrete deck, a modified bitumen secondary membrane isrecommended if the deck has a slope less than ½ :12. If thepanels are installed over a steel deck or wood sheathing, amodified bitumen secondary membrane (over a suitable coverboard when over steel decking) is recommend, followed byrigid insulation and metal panels. Where the basic wind speedis up to 110 mph, a minimum 2-inch thick layer of insulationis recommended. Where the speed is between 110 and 130mph, a total minimum thickness of 3 inches is recommended.Where the speed is greater than 130 mph, a total minimumthickness of 4 inches is recommended. Although some clipsare designed to bear on insulation, it is recommended thatthe panels be attached to wood nailers attached to the deck,because nailers provide a more stable foundation for the clips.If the metal panels are blown off or punctured during ahurricane, the secondary membrane should provide watertightprotection unless the roof is hit with missiles of very highmomentum. At the roof shown in Figure 3-87, the structuralstanding seam panel clips bore on rigid insulation over a steeldeck. Had a secondary membrane been installed over the steeldeck, the membrane would have likely prevented significantinterior water damage and facility disruption.m Based on field performance of architectural metal panels inhurricane-prone regions, exposed fastener panels are recommendedin lieu of architectural panels with concealed clips.For panel fasteners, stainless steel screws are recommended. Asecondary membrane protected with insulation is recommended,as discussed above for structural standing seam systems.MAKING CRITICAL FACILITIES SAFE FROM High Wind3-109

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