b'TECHNICALKEEPING LONG-SPAN ROOFING WEATHERTIGHTBy: Kenneth J. Guffey, PEP ost-frame construction is continuing to expandmovement, for example, can overload panel endlaps its footprint. Part of this expansion involvesand cause them to become compromised over time, much larger structures than was common justresulting in moisture getting past these panel endlaps. a few years ago. Improved materials and expandedThere are several load cases that generate the forces design knowledge have helped to increase the numberknown to cause roof system movement. Currently, there and size of these larger structures. Post frame can noware only a few known effective solutions to prevent handle building widths well over 100 wide, and heightsand repair post-frame panel endlaps and other areas of 20 or more at the eave are possible. Even in this sizethat become compromised. Differences in building range, post frame can provide a structure that meetsdesign and construction (i.e., truss roof system vs. even the strictest design criteria, at a cost that is verypost and beam roof system), differences in building competitive relative to other types of construction. materials (i.e., 100 percent aluminum vs. steel roofing), One of the design considerations now getting increasedetc., make a universal solution difficult. However, with attention is how to effectively use traditional, exposed- a better understanding of roof system movement, fastener metal roofing panels in these large structureeffective panel endlap designs and other solutions applications. Multiple panels are needed to reach fromcan be identified to allow the roof system to remain eave to ridge, creating the need for panel endlaps.weathertight over its life span.WhenallaspectsoftheroofsystemdesignandThe focus of this article is the roof panel endlap, installation are not carefully considered, these largerecognizing that other areas of the roof system can also structures can develop weathertightness concerns atexperience damage (i.e., other shear transfer areas, the roof panel endlaps and other areas. The buildingsetc.). More work needs to be done to understand roof contents, as well as the structure itself, can be damagedsystem movement and the interaction between the when moisture is allowed to get past the roof systemvarious roof system components. Over the past several and enter the building. years, Rigidply Rafters Inc. has investigated numerous Leaking roof systems are not acceptable. Roof systemprojects, has viewed their roof system weathertightness 12 www.mrca.orgMidwest Roofer'