The critical role of metal fasteners in roof construction
Roofs designed for maximum performance and durability can extend the life of the structure by providing protection from the elements, resisting uplift, and transferring horizontal and vertical loads to the building frame. Metal fasteners play a fundamental role in properly designed and installed roofs. According to FEMA’s “Local Officials Guide for Coastal Construction,” evaluations of coastal buildings damaged during high-wind events show that structural failures often begin with the roof, and more specifically, with connection failures. Factors, such as wind and seismic forces, must be considered not only in the design phase of a roof, but also when specifying fasteners. To maximize structural strength and ensure that the building envelope is not compromised, it is critically important that all of the components of a structure work in concert.
Welds
For decades, welds were the most popular fastening method for steel decking attachments. Welds provide great connection capacities; however, this fastening solution requires that installers be trained and certified for this type of application. This opens the door to tremendous variations in applications based on training, individual skill and experience. According to Dr. Ed Sutt, vice president of fastening systems at Simpson Strong-Tie, Pleasanton, Calif., “Welds require special inspections, but there is no real way to make sure how effectively a weld connection has been executed. It can only be seen from the outside. You can’t really see the quality of the weld by visual inspection.”
Mechanical Fastening Solutions
The industry is shifting from welds to mechanical fastening solutions because of the many benefits associated with mechanical fasteners. Metal fasteners are tested to specific standards to ensure that each fastener offers the same level of performance. Unlike welds, which can vary, mechanical fastening systems can provide greater reliability and a faster installation, resulting in roof assemblies completed to code in less time. High-performance metal fasteners have been shown to perform as well as, and in some cases better than, welds.
Auto-feed Screw Driving Systems
Auto-feed screw driving systems are now available that provide a performance-proven alternative to other less-efficient methods of attaching steel decking. Unlike welding and powder-actuated tools, no special inspection or certifications are necessary. Additionally, collated fastener strips virtually eliminate fastener waste and the need to handle individual screws. This facilitates a faster installation while reducing costs. Added benefits include the elimination of the costs of welding leads, welding rods, portable welders and fuel.
For example, Quik-Drive auto-feed screw driving systems from Simpson Strong-Tie can be used to efficiently attach structural and side lap attachments. The Strong-Drive XL Large-Head Metal screws with 5/8-inch diameter hex washer head are designed for high shear strength and maximum uplift resistance for profiled steel diaphragm applications. They are high-performance screw alternatives to welds and pins and have approval reports including IAPMO UES ER-326, FM Approval #3050714, Florida Approval #FL16937, City of Los Angeles
#RR26009 and SDI DDM03 Appendix IX. For assistance with selecting metal fasteners for metal roof construction, The Metal Construction Association has published “Fastener Compatibility with Profiled Metal Roof and Wall Panels.” This bulletin provides important information to consider when specifying fasteners.
Residential Metal Roof Fasteners
High-wind events, such as Hurricane Katrina along the Gulf Coast and Hurricane Sandy in the Northeast, have put local residential building codes in the spotlight. Although the International Building Code establishes and governs design standards for new home construction, and now requires homes to be built with a continuous load path, there are still certain parts of the country where codes are not enforced.
Strengthening the structural frame of homes can be accomplished with a system of wood, shear walls and metal connectors to connect the roof to the structural frame. Research, as well as historical evidence, shows that structural connectors and fasteners increase the strength of a home, resisting the powerful effects of storms or earthquakes that can damage the building envelope. A toe-nailed connection was once standard practice in residential construction. However, during high winds and earthquakes, nails tend to pull or pop out. Builders who choose to use metal roof fasteners can offer this benefit as an upgrade, differentiating these well-constructed homes from others in the same area.
Expense and Performance
Adding connectors is a relatively inexpensive investment. Depending on the size of the home, upgrading to metal connectors and fasteners can cost between a few hundred dollars and a few thousand dollars. This cost is nominal when compared to the cost of repairing or rebuilding a home.
In both residential and commercial construction, structural connectors and fasteners can make a significant difference in the durability and life of the structure. Investing in performance-tested metal fasteners can mean less damage and fewer repairs in the face of high-wind and seismic events.
Neelima Tapata is a research and development engineer at Simpson Strong-Tie Co. Inc., Pleasanton, Calif. To learn more, visit www.strongtie.com.
