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Stitch screws or not on steel roofing panels?

etting | Posted in General Questions on

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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Replies

  1. Expert Member
    MALCOLM TAYLOR | | #1

    Jeff,

    I agree. Stitch screws, especially with that gauge metal, are prone to backing out and don't have enough meat to hold onto keep the washer tight.

    I haven't any good argument to give the inspector beyond that practical one. However, unless you have broached the topic with them, I'm wondering how they would ever know. Our inspectors never look at roofing, or climb roofs.
    I'm not suggesting you lie to them, but there are all sorts of things on a build that you could get an inspector interested in if you try.

  2. user-36575 | | #2

    @ Malcolm, re getting inspectors interested in something else:
    a senior engineer that I knew used something he called "bitch-deflectors". Prior to a design review, he would intentionally include a design feature that was not good or correctly controlled. He knew that he could argue about it during the review, and eventually concede the argument, and the other party would feel good about contributing to improving the design, while the truly key features of the design slid through without too much discussion.
    I learned a lot from that engineer. Fun memories, too.

  3. Expert Member
    MALCOLM TAYLOR | | #3

    Andrew,

    That's a good idea. Generally I just fake a sudden injury.

  4. etting | | #4

    Thank you, Malcolm. The practical argument should be persuasive--if ever needed.

  5. georgeoliver | | #5

    Great idea , installation now can be done perfectly.
    http://www.dannysonroofing.com/

  6. Expert Member
    MALCOLM TAYLOR | | #6

    George,
    Can you re-link that? I don't see any new details.

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