b"THE OFFICIAL NFBA MAGAZINEKEEPING LONG-SPAN ROOFINGWEATHERTIGHT By: Kenneth J. Guffey, PERESEARCH & TECHNOLOGYFigure 1P ost-frame construction is continuing to expand its footprint. Part of this expansion involves much larger structures than was common just a few years ago. Improved materials and expanded design knowledge have helped to increase the number and size of these larger structures. Post frame can now handle building widths well over 100' wide, and heights of 20' or more at the eave are possible. Even in this size range, post frame can provide a structure that meets even the strictest design criteria, at a cost that is very competitive relative to other types of construction.One of the design considerations now getting increased attention is how to effectively use traditional, exposed-fastener metal roofing panels in these large structure applications. Multiple panels are needed to reach from eave to ridge, creating the need for panel endlaps. When all aspects of the roof system design and installation are not carefully considered, these large structures can develop weathertightness concerns at the roof panel endlaps and other areas. The buildings contents, as well as the structure itself, can be damaged when moisture is allowed to get past the roof system and enter the building.Leaking roof systems are not acceptable. Roof system movement, for example, can overload panel endlaps and cause them to become compromised over time, resulting in moisture getting past these panel endlaps. There are several load cases that generate the forces known to cause roof system movement. Currently, there are only a few known effective solutions to prevent and repair post-frame panel endlaps and other areas that become compromised. Differences in building design and construction (i.e., truss roof system vs. post and beam roof system), differences in building materials (i.e., 100 percent aluminum vs. steel roofing), etc., make a universal solution difficult. However, with a better understanding of roof system movement, effective panel endlap designs and other solutions can be identified to allow the roof system to remain weathertight over its life span.The focus of this article is the roof panel endlap, recognizing that other areas of the roof system can also experience damage (i.e., other shear transfer areas, etc.). More work needs to be done to understand roof system movement and the interaction between the various roof system components. Over the past several years, Rigidply Rafters Inc. 28 / FRAME BUILDER - VOL5 1"