Standing Seam Fastener Essentials

Standing seam metal roofs use raised, interlocking, dual seams to connect their panels together. Contractors build these roofs vertically, from eaves to ridge. Concealed fasteners with a clip or nail flange system provide built-in allowance for the expansion and contraction of the metal panels with temperature change. Protected from weather elements, these hidden fasteners are secured to the roof to hold the panels in place while still allowing the panels to float with expansion.

A critical component to connecting the roof to the building structure

By Mark Robins

Photo courtesy of Direct Metals Inc.

“Standing seam fasteners play a critical role in metal construction,” explains Josh Krohn, engineering services manager, Triangle Fastener Corp., Cleveland. “They are the connection between the standing seam roof and the building structure. Fasteners used for standing seam roofing should be produced to industry standards such as ASME B18.6.3, SAE-J78 and ASTM C1513-18. To ensure good quality, you should use fasteners from a supplier who can certify their compliance to standards like these. [Meeting industry standards and minimum requirements] reduces variations in strength from manufacturer to manufacturer for the same sized fasteners. As the diameter of the fastener goes up, so does the strength. Using the specified fastener size per the roof system designer will ensure good performance.”

Photo courtesy of Dynamic Fastener

Low-Profile Considerations

Standing seam metal roof panels use fasteners under the panel screwed through clips. “The clips have vertical legs that nest within the panel side joint, and when the roof is seamed these tabs are rolled and formed into that seam of the panel,” says Peter Graves, vice president of engineering and technical services, ST Fastening Systems, Tyler, Texas. “The screws for the clips are usually a pancake head or wafer head to keep a low profile to hide below the panel. For installation into wood substrates, they can be stainless steel or spin dip-coated, and for steel purlins, there are self-drilling screws. Clips come in several options: fixed, articulating, low-floating and some high-floating clips. These clips allow for thermal expansion to occur without binding while trying to move the purlins or substrate. The high floating clip allows for insulation to be installed between the panel and substrate.”

“Low-profile standing seam fasteners are available to fasten clips to wood or steel,” says Ken Webb, sales manager, Dynamic Fastener, Kansas City, Mo. “T-17 point acts as a self-driller into wood and a self-drilling point is required when drilling into steel.” Steve Butler, sales manager at Dynamic Fastener, explains that when choosing a standing seam clip screw, “The most important detail is choosing the proper fastener to attach clips to the substrate. If fastening into wood or plywood one would want to choose a #10, #12 or #14 Type 17 clip screw. These clip screws have a flat pancake head.”

Photo courtesy of LSI Group

Andrew Mullen, president of Direct Metals Inc., Fort Myers, Fla., explains the reason pancake head fasteners are used instead of traditional hex-headed construction fasteners is that they have a low-profile internal drive design allowing a low-installed profile while still maintaining a load-bearing surface beneath the head of the fastener. Also, “Standing seam panel fasteners can consist of one or two components, in the case of nail strip or nail fin snap lock standing seam panels only a screw fastener will be required. Most other standing seam panels such as mechanical locking, snap lock and batten seam panels require a metal panel clip to working with a Panclip screw fastener [from Direct Metals] to secure the system to the substrate. Standing seam panel fasteners for nail strip panels will feature a wafer-style thin head such as a Panclip XLP (extra low profile) fastener that fits in the nail fin part of the panel providing the lowest installed profile to avoid fastener telescoping or showing through the installed panel.”

Other Differences

In addition to having a low-profile head to prevent interference with the next panel being installed over the top of it, standing seam fasteners have other unique attributes. “[They] differ from through-fastened fasteners in that they do not have separate bonded or EDM washers,” Graves says. “Standing seam roof fasteners have a recessed internal driving system using a square drive, cross top or torx driving system. Through-fastened roof fasteners drive using a hex head driving system.”

Krohn explains, “A screw with a low-profile head typically requires an internal drive bit for the screw gun. This bit goes into a square or star shaped recess in the screw head. The most common head for structural or other fasteners is a hex washer head which requires a hex driver for the screw gun. It engages the outside of the hex and often has a magnet inside.”

Photo courtesy of ST Fastening Systems

The Load Path

Robert Baker, president of LSI Group (Logan Stampings, BPD, Roof Hugger), Logansport, Ind., cautions, “If the fasteners fail, so does the entire system. Fasteners are a very critical component.”

Baker’s company focuses on standing seam clips, and he stresses that, “Their form and function are critical to the performance of the roof. We consider how much they must move, how they will properly fold into the panel seams, where they are weak and how to stiffen those areas. All important stuff but there is one pesky thing engineers call load path. We build some of the strongest clips in the market, to hold the strongest panels in the market but none of this strength will develop unless the fasteners properly secure the clips to the structure below. The load path is the trail of the forces of uplift, download and shear that must pass through the panels into the clips, then to the fasteners and finally down to the structure below. All standing seam panels are tested using a specific test criterion. The ASTM E-1592, FM 4471 and UL 580 and 1897 tests all help to define a system’s total capacity. When you are reviewing a particular panel system look up or ask the supplier for their test results. It will define the panel profile, the attachment clips and the type and quantity of fasteners that were used to achieve the stated results.”

Baker suggests taking the time to read about “how the panel you intend to use is attached, what clip and what fastener is specified. The type, number and location of the fasteners can determine the overall roof systems performance. Failure to comply with the manufacturers recommendations can also adversely affect the warranty of their roof system.”

Photo courtesy of Triangle Fastener Corp.