As with fixing all types of roofing material, there are certain guidelines to follow on how to screw polycarbonate roofing, some of which, are rules that work in general, and others which are specific to polycarbonate sheets.
Since flat profiled polycarbonate sheets such as Solid Flat, Solid Embossed, and Hollow profiles are normally fixed in, or on top of frames, and which the screws required are more directed towards fixing the frame itself and seldom, if ever, come in contact with the actual polycarbonate sheets; this article will focus on how to screw polycarbonate corrugated profile roofing sheets.
A major difficulty with fixing non-metallic sheeting such as polycarbonate sheets is its relatively high coefficient of thermal expansion. Current industry practice is to ream a I0mm hole in a non-metallic roofing profile to install a #12, 4.5mm diameter screw. This requires two tools, two operations and a reasonable amount of time, effort and skill. It is a significant time-consuming procedure. Oftentimes, screws are positioned at one side of the hole, instead of in the center, which can result in insufficient clearance for expansion in the relevant direction.
Another difficulty in the installation of sheet roofing profiles is screw over-run or over-drive. This is the over-tightening of fixing screws such that there is a squashing of the raised profile through which the screw is passed. It is quite common for even professional installers to overdrive a fastening screw, squashing the relevant ridge in the profile, and requiring them to reverse the screw rotation in a secondary operation to bring it to the correct position. Not only does this procedure take more time than necessary, but it may also damage the sheets.
Poly-Fast and PolyXpand fasteners were invented and designed for affixing to an underlying structure, in most cases steel or timber purlins and battens, architectural sheet profiles made from polycarbonate which have a high coefficient of thermal expansion.
During the drill and drive process, the cutting saw on Poly-Fast and the drilling-tip wings on PolyXpand both creates an 11mm diameter thermal expansion hole, which is then completely covered by the extremely durable domed EPDM washer to create a perfect seal against the elements.
To prevent damage from overdriving screws and damaging the sheets underneath, Poly-Fast polycarbonate screws have an additional knurling on the shaft right after the threads. Normally, knurls on metal roofing screws acts as a brush to clear off excess swarf created during the drill and drive process. On PolyFast fasteners however, the knurl acts a stopper for the round cutting saw, the height at where it stops upon coming in contact with the purlins is designed to match the pitch of VULCAN polycarbonate ROMA and GRECA profiles; enough so that it provides a perfect seal on the enlarged hole, but not deform the corrugations.
When working with PolyXpand fasteners, it is absolutely critical to drive the screw perpendicular to the sheets, and not to the point that the washer is squished, which will result in the washer losing its flexibility, and a gaping hole gouged out by the hex washer flange.
VULCAN accessories are designed to work seamlessly with VULCAN Polycarbonate sheets. Consult VULCAN or your local dealer before using any non-conforming accessories. Failure to do so could result in damaging VULCAN Polycarbonate sheets and void warranty.