Use The Right Fastener Stephen Childs, Technical Services Manager, OMG Roofing Products Commercial, industrial and institutional buildings can be constructed with several different roof deck types, including steel, wood, concrete, gypsum and others. Each has a unique set of characteristics that require different mechanical fasteners to meet the various needs of the roof assembly. Regardless of the specific deck type, contractors should always ensure that the fasteners used to secure any roofing components are proven for the application and are code-compliant (e.g., Factory Mutual, Miami-Dade County). Since first used to attach insulation in the early 1980s, roofing fasteners have evolved a great deal. Prior to 1980, fasteners had not been specifically designed or engineered for commercial roofing applications. Fastener pullout, back-out and corrosion resistance requirements were unknown and, as a result, fastener performance was not always up to the task. As fastener manufacturers started working closely with roof system manufacturers, more sophisticated and task-specific roofing fasteners were developed. At first, wood and steel were the only roof decks suitable for mechanical fastening. Cementitious wood fiber (Tectum), gypsum, lightweight insulating concrete and even structural concrete decks possessed unique properties that did not allow insulation or membrane to be secured with traditional screws. Fastener manufacturers began to recognize the roofing world as a new opportunity and dedicated resources to design and engineer products to address market demands. New fastener companies solely dedicated to the roofing industry emerged, bringing with them new fastener designs and better performance. Below is a general description of the most common decks and fastener options.
new designs for specific applications. Today, there are a wide variety of roofing screws for steel deck applications. The specific screw used depends on the component being installed. Membrane and insulation fasteners have different performance characteristics and are not generally interchangeable. “Standard” screws, often referred to as #12, are typically used to secure insulation (Figure 1), while larger diameter screws (#14, #15 and #21) are typically used to secure membrane. These larger diameter screws also have buttress style thread designs (Figure 2) as well as point configurations that maximize pullout and backout resistance for improved wind-uplift resistance. Insulation attachment is less dynamic and insulation fracture is more likely to occur than fastener pullout, so insulation screws are less sophisticated in design.
Figure 1: #12 Standard Drill Point Fastener
Steel Deck
The most common commercial roof deck is steel and it is available in several different configurations, thicknesses (gauge) and tensile strengths. Thickness and tensile strength play a major role in fastener performance. It’s important to understand that when a screw pulls out of a steel deck, it’s the deck that fails not the screw but there are some fastener designs that perform better than others. The change in test protocols at Factory Mutual in 1992 – after Hurricane Andrew severely damaged South Florida – from a 5’ x 9’ to the current 12’ x 24’ test sample size for all mechanically-attached systems over 4-feet wide and for fully adhered, built-up and modified bitumen systems requiring wind uplift ratings over 90 psf, not only exposed the limitations of many of the screws used in steel roof decks at the time but also helped spark 20
FLORIDA ROOFING | March 2022
Figure 2: Buttress Style Tread Design
Regardless of the screw type, all steel deck fasteners are designed to be used with a stress plate that has also been designed for the specific application. Most roof cover manufacturers have fastener programs and generally require the use of their fasteners to comply with warranties. Approval listings, especially Factory Mutual approved systems, also have minimum deck requirements. The roof cover manufacturer should always be consulted for specific deck and fastener requirements.
Wood Deck
Dimensional lumber, plywood and oriented strand