Ultimately, a major concern with the specification of any roof system is that system’s ability to withstand potential high winds and uplift pressures. In many cases, this is an issue not only of metal roofing product design but also of the condition of the roof deck or other substrate and the ability of that substrate to withstand pull-out of the fasteners.
In the case of deteriorated roof decking, the ability to withstand fastener pull-out will be diminished. This happens when the decking perhaps had quality problems to begin with or when it has diminished over time perhaps due to insufficient attic ventilation (see Technical Bulletin #15). It also can happen in the case of fire-treated decking (see Technical Bulletin #22) or when roof leaks have caused the decking to rot. Another issue can be unusual decking materials such as Tectum (see Technical Bulletin #41). The amount of fastener pull-out resistance required varies between panel designs. Thicker, more heavily formed metal roof panels will ultimately be subject to increased uplift pressures, requiring greater fastener pull-out resistance. When concerns about fastener pull-out exist, it is important to communicate with the product manufacturer for their input and expertise. Additionally, one must consider whether the roof deck’s ability to resist pull-out can be expected to lessen as time goes on.
When concerns over pull-out resistance exist, they can be somewhat addressed through using screws instead of nails and also by increasing the overall number of fasteners installed with the roofing. More fasteners means less uplift pressure on each individual one. There are tools available for checking pull-out resistance. However, by using a farm scale with a loop of steel strapping attached to the weight end and the fastener driven through the loop, one can do a reasonable “homemade” evaluation of pull-out resistance. (Proper safety steps must be taken when performing this on a roof surface.) It is Classic Products’ opinion that any cases where less than 100 pounds of resistance are found should be subject to further research and evaluation.
Classic Products, Inc.