The positive effects of sliding pins versus set screws
With the rise in popularity of rooftop solar panels, engineers at Plainville, Conn.-based AceClamp/PMC Industries began asking the manufacturers of standing seam metal roofs (SSMR) what their major concerns about solar panel roof installations were.
Two concerns immediately stood out.
Because standing seam metal roofs are designed to be installed with no exposed fasteners, the first requirement was that fastener installation should cause no penetrations through the roof surface. Secondly, there should be no scratches to the roof finish. After all, coil coaters have worked long and hard to develop high-performance finishes that allow the panels to be rollformed to the roof’s configuration, and to withstand years of hot sun, salt air and the myriad of pollutants that can collect on a rooftop.
With these two requirements in mind, AceClamp eliminated set screws as a means of securing clamps to metal roof panels. Effective as some set screws can be, there was the concern that, if improperly installed, the roof panels’ polymer coatings could be damaged by the rotational action of the set screws, potentially voiding the roof manufacturer’s warranty. AceClamp already had a patented, non-penetrating clamp designed to fit over the larger “T” and “Zip” rib configurations. Tightening the top-mounted hex bolt, the two halves of AceClamp’s ML clamp move together to squeeze across the SSMR rib with enough tension to keep a photovoltaic (PV) array on the roof during the most severe wind loads and, importantly, without damage to the roof surface.
But because the ML version was larger than needed for some of the more common roof configurations, the AceClamp team ultimately settled on, and patented, a smaller profile design (the A2) that incorporated two sliding pins driven by a single 9/16-inch hex head bolt.
There is no rotational motion with the A2, as the pins close or push against the SSMR rib and, if installed properly, no scratching of the roof coating occurs. Also, load testing by third-party laboratories shows that the clamp-to-rib fastening is generally strong enough to meet the most demanding wind uplift building codes.
Positive Effect
The positive effect of sliding pins versus set screws is even more obvious when accessories are installed over standing seam metal roofs that have been rejuvenated with a liquid-applied roof system. There are thousands of roof square feet that have been subjected to more than 20 years of salt spray, pollution and excessive activity that damages or removes rooftop components. The roofs might still be watertight, but the seams could be in need of repair, or the surface is discolored from corrosion. Rather than replacing the roof, a liquid-applied system is sprayed or rolled onto the surface creating a 0.03-inch to 0.04-inch membrane-like protective coating. But now the owner decides to install a solar array. This is a case where the rotational motion of set screws will easily penetrate the new coating to the bare metal, voiding a brand new warranty. A clamp with sliding pins, however, will grip the SSMR rib without penetrating through the coating: warranty maintained!
Static load testing show the force required to cause a clamp to fail, either from an upward force (wind uplift) or from a force parallel to the roof plane (snow loading). Some building code groups, especially on the West Coast, have been concerned that continuous seismic vibrations could cause set screws to loosen. To address that issue, a vibration test was created at AceClamp’s development labs.
An AceClamp fastener was attached to a section of roof panel and tightened to a specified torque level. A weight was attached to the top of the clamp, the panel tipped to a 30-degree incline, and the vibratory unit started. After 750,000 cycles, the unit was stopped and the torque on the hex bolt measured. The resulting torque was within 5 percent of the initial torque levels. The secret of this performance was the soft, flat washer inserted between the serrated flange and the hex bolt.
Upon tightening the bolt to the torque limit for the SSMR, the flange serrations embedded into the washer. The pins on the opposite face of the washer formed shallow grooves into the washer face. The combination of the grooves and the serrations acted like a lock washer preventing any back out. This is important in any application, whether it is an installation in a seismic area, a rooftop subject to vibration from machinery on the floor below, or a solar array on the roof where winds blow continuously causing the array to flutter.
Caroll Marston is AceClamp sales engineer at PMC Industries Inc., Plainville, Conn. To learn more call (860) 428-4970 or email
cemarston@pmcind.com.
