b'TECHNICALIncreasing the number of fasteners at and aroundRoof panels in most post-frame structures try to help the panel endlap has been helpful in more effectivelythe structure carry various loads. These light-gauge roof handling the forces at the panel endlap. It is commonsystems have limits to their structural capacity. This is to use the double fastener endlap pattern not just atparticularly true of the fastener connection between the the panel endlap, but also at least in the adjacentroof panels and the wood purlins. upslope and downslope purlins. Panel endlaps andMore work is needed to understand these higher, wider, adjacent purlins that utilize the beefed up doubleand longer post-frame structures relative to their roof fastener pattern have fewer issues, particularly inpanel system behavior, and to further explore potential two-piece roof applications (i.e., only one panelsolutions to issues that develop. Preliminary work and endlap in an eave to ridge panel run). observations indicate that effective solutions can be 7. Fasteners applied to the top of roofing panel ribsdeveloped and will vary depending on a variety of have fewer issues than fasteners applied throughbuilding parameters. the flat of the panel. Fasteners applied to the topKeeping in mind that panel endlap issues are often of the panel ribs effectively create a gap betweencaused by a combination of different loads/forces, the fastener/panel intersection point and the woodsolutions must consider all these potential forces and purlin underneathtypically this gap isor thenot just panel expansion and contraction. For example, height of the panel rib. This gap allows the fastenerareas of a roof system can be strengthened such that shank to flex to some degree without damaging themovement is relocated to areas better able to handle wood purlin or the panel. However, there is a limitthis movement (i.e. beefing up panel endlap fastening to how much movement can be handled with thispatterns). In other cases, movement is simply too great connection design. and must be reduced through a stronger and stiffer 8. Southern Yellow Pine (SYP) purlins have an openframe design. In yet other situations, particularly very cell structure vs. Spruce-Pine-Fir (SPF) purlins.long eave to ridge distances, the roof panels must not Fasteners tend to back out of SYP much easierbe connected in any way to any adjacent roof panel. than SPF due to SYPs open cell structure allowingThis slip joint approach, as illustrated in Figure 1, is moisture to move quickly and frequently in and outbecoming more common because it is very effective in of the wood. These wood purlin moisture contentsolving the endlap weathertightness issue. However, changes encourage fastener backout. careful consideration must be given to the structural 9. The south side of a structure has more endlapimplications of un-connecting roof panels from each issues than the north side. Those slopes that seeother, particularly due to the fact that many post-frame the sun first warm up faster each day. The faster thestructures depend heavily on the roof system diaphragm temperature rises, the faster the roof panels expand.for at least some structural support.This rate of expansion makes a difference andContact your building design professional and your causes more issues than slower rates of expansionroof panel manufacturer to collectively establish an and contraction. Expansion and contraction relatedeffective approach to connecting your roof panel system endlap issues are not just from the annual changesto your structure, and to establish a reliable approach in temperature but are also from the more frequentto handling your panel endlap design. Taller, wider and daily changes in temperature. longer post-frame structures offer many benefits to 10. Insulation applied directly under the roof panelstheir owners and are here to stay. Our industry needs elevate the actual roof panel temperature duringto realize that post-frame structures are not temporary thosemoreintensesummerdays. Thisfurtherstructures but are in fact structures that the building increases the expansion/ contraction panel lengthowner expects to utilize for many years, in applications changes in the roof panels. The net result is morewith high expectations for performance, appearance, movement at the panel endlaps. and weathertightness. FBNCommentary Kenneth Guffey, PE, is general manager at Rigidply Rafters Inc., in Richland, PA, and can be reached at Roof panel fasteners connect the roof panels to the woodkenguffey@rigidply.com.framing underneath, and therefore transfer forces into and out of the roof panels of the post-frame structure. 14 www.mrca.orgMidwest Roofer'