Over the past several months we’ve talked a lot about standing seam panels and their ability to resist all kinds of weather-related challenges as well as fire, hurricanes and salt air. We’ve compared Galvalume to galvanized steel, polyester to PVDF coating and different metal and aluminum gauge thicknesses.
But the one thing we haven’t talked about are the two different types of metal roofing fastening systems—a very important topic that involves economics, aesthetics and maintenance.
Image may be NSFW.
Clik here to view.
The two most common ways of attaching a metal roof to a structure are exposed fasteners and concealed fasteners. Exposed fastened panels use a screw or nail to secure the metal roofing to the roof deck or purlins whereby the nail or screw actually penetrates an area where two panels overlap. This can involve hundreds and even thousands of fasteners which must be spaced and driven to maintain the integrity of rubber grommets which serve to prevent precipitation from gaining access through each hole.
Conversely, concealed clip fastened panels use a system where the fasteners are driven through the clips into the roof deck with no connection or piercing of the metal panels. The clip and fasteners are concealed beneath the standing seam panel material. The panel is then laid over and attached to the clips and then mechanically or hand locked to them.
Granted, exposed fastener metal roofing panels are a less expensive alternative to concealed fastener standing seam roofs. They work best in simple roofs like gables or shed roofs but get difficult to work with on structures with dormers, valleys and complex architectural features.While many people swear by them and have enjoyed years of service from them, exposed fastener roofs have lesser warranty times than concealed fastener systems. Problems can occur if the fasteners are driven too tight by the contractor or installer. Because metal expands and contracts with temperature change, screws driven too tight leave no room for expansion and contraction. In contrast, a concealed fastener system is driven through the clip and not the panel itself and is designed to flex or move under the panel. And of course, the concealed fasteners are never exposed to the weather and are insulated from the movement.
Cost will differ depending on location, but concealed fastener is more expensive because of the clips and the time it takes to install the hidden fasteners. Their biggest benefits are peace of mind and aesthetics. Instead of hundreds or thousands of tiny holes filled with screws with an oversized cap head, you have an aesthetically smooth surface broken only by the seams which give the concealed fastener system its elegance. Because of this aesthetic, concealed systems are seen largely on residential and commercial structures while the exposed fastener system is more likely to be found on large industrial and commercial buildings.
Some building owners will tell you their exposed fastener systems have stood up to precipitation and UV light from the Sun for years. But unlike concealed fastener systems, the warranties are shorter and less robust and some experts suggest that screws be randomly backed out periodically to see if the grommets are intact and still snug in the drill holes and the wood substrate is free of any dampness.