board (OSB) can all be used in wood roof deck construction. Currently there are not any commercial roofing fasteners on the market specifically designed for use in wood decks. Instead, steel deck screws – especially the “standard” screws – are commonly used in wood substrates due to a coarser thread profile that provides the best pullout resistance for wood. In addition to the “standard” fasteners, #14 “heavy duty” or allpurpose fasteners (Figure 3) can also enhance pullout resistance in wood decks. The pullout resistance values in dimensional lumber are usually high due to the thickness and density of the wood. However, in plywood and OSB, especially in boards less than 3/4-inch thick, obtaining consistent and adequate pullout values can be very challenging due to limited thread engagement and voids in the laminations. This is of concern with mechanicallyattached single-ply, where the wind uplift forces are more dynamic. Having a qualified technician perform a fastener pull test is recommended for plywood and OSB construction or where there is question of the roof deck’s condition.
connection with the fastener fails. This is because movement of the insulation or roof cover moves the screw back and forth and the deck is not resilient enough to take this movement. The deck becomes damaged, greatly diminishing the pullout resistance. The fastener performance can become inadequate to support the roof assembly. The same auger-type fasteners that are used for cementiFigure 5: OlyLok tious wood fiber are used
Figure 3: #14 Heavy Duty Fastener
Cementitious Wood Fiber
Some roof decks, like cementitious wood fiber, are not capable of holding a “traditional” screw. The wood fiber and cement construction are simply not dense or stable enough to hold small-diameter, shallow-thread screws. Instead, large-diameter coarse thread auger-type fasteners made from glass-filled nylon (Figure 4) were developed to accommodate the varied density of these decks. Some can be installed without Figure 4: GypTec pre-drilling; however denser decks Fasteners typically require pre-drilling. There are other fasteners with this general design that are made from steel and look like monster screws. It is also common to attach base sheets to this kind of deck. Drive-type fasteners with barbs that extend into the deck (Figure 5) after the fastener is seated, provide an excellent attachment method. A fastener pull-test is a must with this type of deck.
As with cementitious wood fiber decks, gypsum roof decks do not effectively hold traditional roofing fasteners. While many have tried putting concrete screws into this type of deck and have even achieved relatively high pullout resistance, over time the deck FRSA third page.indd 1
www.floridaroof.com | FLORIDA ROOFING
10/19/2020 10:01:24 AM