Stitch screws or not on steel roofing panels?
I’m installing 29 ga Classic Rib steel panels on a simple gable roof with a 4:12 pitch. The panels are 12’9″ long from the peak to the end of a 2′ overhang. They are attached to 2×4 purlins over underlayment and OSB sheathing. I’m in central Arizona.
The manufacturer’s installation guide for the Classic Rib panels says to install stitch screws every 12″ along the side laps, but the guides from a couple of major retailers of Classic Rib say stitch screws are optional with a 4:12 or greater pitch. They all agree that butyl tape along the side laps is not necessary, as the Classic Rib has an anti-siphoning groove built in. I finally decided to follow the manufacturer’s recommendation, but when I installed the first few stitch screws, they pulled the upper panel’s steel up all the way to the screw’s washer before starting to penetrate the lower panel so that, as the screw penetrated the lower panel, the washer became greatly overcompressed. I ended up having the back the screws out over and over again to get them finally to penetrate the lower panel and seat properly.
I’m using a highly recommended screw gun, the Dewalt DW-268, and I think I’m applying correct pressure. The same problem was occurring on roughly 20% of the wood screws I was installing on the flats, into the purlins, until I stacked the next seven panels and predrilled 3/16″ holes for them, just barely larger than the screw’s diameter, which made everything much easier, neater, and quicker. If I’m going to install any more stitch screws, I’ll predrill holes for the upper panel’s overlapping rib and leave the lower panel to be drilled by the screw itself.
Even if predrilling the upper panel eliminates the problem of the screw separating the panels as it’s driven, I wonder whether stitch screws are a good idea. First of all, fewer holes in the steel seems better, and secondly, as Malcolm pointed out in another, otherwise unrelated discussion, 29 ga steel alone doesn’t seem as if it would hold a screw all that securely, especially as the panels move around with wind and thermal expansion and contraction. The screws in the flats immediately on each side of the overlapping ribs between panels seem to hold the overlap quite securely.
Would you use stitch screws in my application or not? Your comments will help me decide and, if I decide to omit the stitch screws, make a case for the building inspector’s approval.
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