Exposed Fastener Metal Roofing: Is It Standing Seam?
I get a lot of questions about exposed fastener metal roofing. Also called “screw-through” metal roofing or sometimes “channel drain”, these are rollformed products that are vertically oriented on the roof. They have some sort of corrugated wave or rib pattern formed into the panels. Some common names to the corrugated patterns are “R Panel,” “PBR Panel,” and “5V Crimp.” They are installed using screws that penetrate the panels, leaving the screwheads exposed.
Many people refer to these products as “standing seam” roofing. I have even heard contractors call them that. In fact, though, they are not standing seam metal roofing systems. Standing seam products do not have exposed fastener heads and they also have some sort of interlock joining the panels one to the next. Exposed fastener metal roofs have a simple overlap from one panel to the next. Also, whereas standing seam comes in continuous length panels with no seam from the bottom of the panel to the top, exposed fastener metal panels are often in standard lengths meaning there are horizontal overlaps from one panel up the roof to the next.
Exposed fastener panels have had extensive use in the agricultural markets, from barn roofs to metal buildings. Many of these products, depending upon their gauge and design, can be installed over battens or strapping rather than a solid roof deck. With the rapid growth in popularity and awareness of metal roofing in recent years, these products have ended up frequently installed on homes. They install easily and quickly in most cases.
However, when homeowners ask me about these products, I must tell them that may not be getting what they think they’re getting when they buy exposed fastener metal roofs. Most metal roofing customers make their purchase thinking they’re getting the full gamut of metal roofing benefits – long life expectancy, energy efficiency, increased home value, and no maintenance to name a few. In most cases, with exposed fastener metal roofing, though, they are not really getting these benefits.
Exposed fastened products, having been made largely for the very price conscious agricultural market, are often made from lower grade raw materials. They may be G60 (or even less) galvanized rather than G90. They may be AZ 45 galvalume. They may have polyester paint finishes rather than Kynar 500® and Hylar 5000® PVDF resin-based finishes. All of these things affect their life expectancy, often making these products 20 – 25 year products rather than the 50+ year products that homeowners want when they choose metal.
And then there are all of the fastener holes. The average through-fastened metal roof will have hundreds and even thousands of screws penetrating the panels. These screws have washers or grommets on them but those dry out and crack over time. Additionally, because exposed fastened products have no allowance for the metal’s natural expansion and contraction with thermal, cycling, the fastener holes “wallow out” over time. Fasteners can even break from the pressure and fatigue. Once all of this happens, water can penetrate the holes, jeopardizing the protection offered by the roof system and also setting off a process of corrosion of the metal.
As far as maintenance, again, the exposed screws are a problem. The forces from the metal expanding and contraction can cause the screws to loosen. They can be re-tightened but eventually to maintain the roof’s service life, the screws need to be replaced with new screws of slightly larger diameter.
Now, whenever folks ask me about these products, I tell them that they have a decision to make. While these products are indeed metal roofs and they do offer some of the benefits of metal roofing, they also have serious shortcomings. These shortcomings can even detract from, rather than increase, home value over time. Most folks who invest in a metal roof want it to last the life of their home. Exposed fastened metal roofs can leave them sadly short of that goal.
As always, I am happy to answer any specific questions you have about roofing or ventilation. You can email me at firstname.lastname@example.org.
Kynar 500® is a registered trademark belonging to Arkema Inc.
Hylar 5000® is a registered trademark belonging to Solvay