TECHNICAL www.mrca.org — Midwest Roofer 14 Increasing the number of fasteners at and around the panel endlap has been helpful in more effectively handling the forces at the panel endlap. It is common to use the double fastener endlap pattern not just at the panel endlap, but also at least in the adjacent upslope and downslope purlins. Panel endlaps and adjacent purlins that utilize the “beefed up” double fastener pattern have fewer issues, particularly in two-piece roof applications (i.e., only one panel endlap in an eave to ridge panel run). 7. Fasteners applied to the top of roofing panel ribs have fewer issues than fasteners applied through the flat of the panel. Fasteners applied to the top of the panel ribs effectively create a gap between the fastener/panel intersection point and the wood purlin underneath—typically this gap is ¾” or the height of the panel rib. This gap allows the fastener shank to flex to some degree without damaging the wood purlin or the panel. However, there is a limit to how much movement can be handled with this connection design. 8. Southern Yellow Pine (SYP) purlins have an open cell structure vs. Spruce-Pine-Fir (SPF) purlins. Fasteners tend to back out of SYP much easier than SPF due to SYP’s open cell structure allowing moisture to move quickly and frequently in and out of the wood. These wood purlin moisture content changes encourage fastener backout. 9. The south side of a structure has more endlap issues than the north side. Those slopes that see the sun first warm up faster each day. The faster the temperature rises, the faster the roof panels expand. This rate of expansion makes a difference and causes more issues than slower rates of expansion and contraction. Expansion and contraction related endlap issues are not just from the annual changes in temperature but are also from the more frequent daily changes in temperature. 10. Insulation applied directly under the roof panels elevate the actual roof panel temperature during those more intense summer days. This further increases the expansion/ contraction panel length changes in the roof panels. The net result is more movement at the panel endlaps. Commentary Roof panel fasteners connect the roof panels to the wood framing underneath, and therefore transfer forces into and out of the roof panels of the post-frame structure. Roof panels in most post-frame structures try to “help” the structure carry various loads. These light-gauge roof systems have limits to their structural capacity. This is particularly true of the fastener connection between the roof panels and the wood purlins. More work is needed to understand these higher, wider, and longer post-frame structures relative to their roof panel system behavior, and to further explore potential solutions to issues that develop. Preliminary work and observations indicate that effective solutions can be developed and will vary depending on a variety of building parameters. Keeping in mind that panel endlap issues are often caused by a combination of different loads/forces, solutions must consider all these potential forces and not just panel expansion and contraction. For example, areas of a roof system can be strengthened such that movement is relocated to areas better able to handle this movement (i.e. beefing up panel endlap fastening patterns). In other cases, movement is simply too great and must be reduced through a stronger and stiffer frame design. In yet other situations, particularly very long eave to ridge distances, the roof panels must not be connected in any way to any adjacent roof panel. This “slip joint” approach, as illustrated in Figure 1, is becoming more common because it is very effective in solving the endlap weathertightness issue. However, careful consideration must be given to the structural implications of “un-connecting” roof panels from each other, particularly due to the fact that many post-frame structures depend heavily on the roof system diaphragm for at least some structural support. Contact your building design professional and your roof panel manufacturer to collectively establish an effective approach to connecting your roof panel system to your structure, and to establish a reliable approach to handling your panel endlap design. Taller, wider and longer post-frame structures offer many benefits to their owners and are here to stay. Our industry needs to realize that post-frame structures are not temporary structures but are in fact structures that the building owner expects to utilize for many years, in applications with high expectations for performance, appearance, and weathertightness. FBN Kenneth Guffey, PE, is general manager at Rigidply Rafters Inc., in Richland, PA, and can be reached at kenguffey@rigidply.com.
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