b'TECHNICALissues, and assisted with their solutions. Following ispanel lengths has not proven effective on these more a review of these experiences.recent, much larger structures.What Is Happening?2. Roof systems with more than one endlap in an eave 1. Thermal expansion and contraction of the metalto ridge panel run (i.e. three or more panels) have panels generate forces if resistance to this movementmore issues than an application with a single endlap occurs. Any resistance forces generated need to bein an eave to ridge panel run (i.e., two-piece roof). effectively handled, or alternatively the movementApplications with a single panel and no endlaps have of the roof panels must be allowed. Roof panelsfew issues, provided the panel length is below 36 can change in length significantly over their entirefor steel and 20 for aluminum.temperature exposure range. It is not uncommon for3. Endlap issues tend to be more significant at weaker, a steel roof panel to change in length at leastinmore flexible areas of the roof system. Post-frame 40 of panel length from the coldest to the warmeststructures by design have variations in building temperature exposure. Roof panels of 100 percentflexibility/stiffness within the structure. The stronger aluminum move at approximately twice the rate ofand stiffer roof areas seem to resist movement better, steel.and force the issue to weaker, less stiff areas. Roof 2. Tall,wide,andlongpost-framestructurescansystem movement combined with panel expansion structurally tolerate more movement than conventionaland contraction often overload panel endlaps on construction. This increased movement, however,larger structures. The contribution of each, however, can cause problems with building weathertightness.is currently very difficult to determine.The post-frame structure resists the various loads4. With problem endlaps, the top or upslope panel at as an assembled unit. It is important to note thatthe endlap is the most likely to experience endlap even when the roof system is not used as a structuralfastenerholeelongationovertime.Fastener diaphragm by the building design professional in thewashers at these endlaps are typically also damaged building design, it is still part of the structure anddue to the panel movement under the washer. In will take load unless the framing below is stiff andsome cases, fasteners have fractured. Even if roof strong enough to prevent load from entering thissystem movement from weather-related building roof system. In reality, the framing in a post-framedesign loads is minimized through stronger and structure is rarely stiff enough to keep forces outstiffer framing, roof system metal panels expand of the roof system. Therefore, areas such as paneland contract at very different rates than the wood endlaps can become overloaded. framing underneath.Symptoms of Endlap Compromise 5. With problem endlaps, the endlap fasteners often 1. Leaking panel endlaps are observed to be backing out. Butyl endlap sealant tape is commonly omitted at panel endlaps in post-2. Endlap and nearby fasteners backing out frame structures. Water and dirt siphon upslope 3. Holes in the metal panels at the endlaps becomingbetween the endlap panels, creating a visible stain elongated (both steel and aluminum) and dirt line. If the moisture reaches the shank of 4. Endlap fasteners shearing off just below the washer the endlap fasteners between the panels, it enters the building, causing the wood around the fastener 5. Endlap fastener washers tearing and separating shanktobecomewetandweakened,andthis 6. Wood framing deterioration under the endlap area moisture eventually causes the wood to deteriorate. Common Observations with Endlap Compromise This moisture issue reduces the endlap fasteners structural capacity, promoting fastener backout. 1. Individual roof panel lengths in applications requiringButyl endlap sealant tape needs to be installed in endlaps tend to be 24 or less for steel, and 168panel endlaps. We cant just worry about handling orlessforaluminum.Individualpanellengthsthe forces involved with the endlapwe must keep longer than these values have a significantly higherthe endlap dry.frequency of endlap issues. Reducing individual panel lengths below these values does help to6. 1 long roof panel fasteners have fewer issues reduce endlap issues and has historically been thethan 1 long roof panel screws in larger structures. industrys suggestion. However, reducing individualLarger diameter screws also have fewer issues. www .mrca .orgMidwest Roofer 13'