47.5 MB - The Whole Building Design Guide

Edge Flashings and CopingsRoof membrane blow-off is almost always a result of lifting andpeeling of the metal edge flashing or coping, which serves toclamp down the membrane at the roof edge. Therefore, it is importantfor the design professional to carefully consider thedesign of metal edge flashings, copings, and the nailers to whichthey are attached. The metal edge flashing on the modifiedbitumen membrane roof shown in Figure 3-61 was installed underneaththe membrane, rather than on top of it, and then strippedin. In this location, the edge flashing was unable to clamp themembrane down. At one area, the membrane was not sealed tothe flashing. An ink pen was inserted into the opening prior tophotographing to demonstrate how wind could catch the openingand lift and peel the membrane.Figure 3-61:The ink pen shows anopening that the windcan catch, and causelifting and peeling of themembrane.ANSI/SPRI ES-1, Wind Design Standard for Edge Systems Used in LowSlope Roofing Systems (2003) provides general design guidance includinga methodology for determining the outward-acting loadon the vertical flange of the flashing/coping (ASCE 7 does notprovide this guidance). ANSI/SPRI ES-1 is referenced in the IBC.ANSI/SPRI ES-1 also includes test methods for assessing flashing/coping resistance. This manual recommends a minimum safetyfactor of 3 for edge flashings, copings, and nailers for critical facil-3-76 MAKING CRITICAL FACILITIES SAFE FROM High Wind