Making the Connection
The critical role of metal fasteners in roof
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.
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
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.