Standing Seam Metal Roof On A Bar Joist Roof
Standing Seam Metal Roof On A Bar Joist Roof
(OP)
I found a few old posts on this subject, but they weren't completely helpful. In my situation, the owner's contractor has requested that we use a standing seam metal roof on a new 53' x 64' on a clearspan bar joist structure with CMU bearing walls. The building is about 20' tall. I know that the metal roofing cannot be used as a diaphragm to brace the building. In addition, the metal roof slopes in the direction of the 53' bar joist length, so a sub-purlin system system is needed perpendicular to the joists at 5' on center max. But then there's the matter of providing a roof diaphragm. Reading the literature will tell you that you either need to provide horizontal x-bracing in the plane of the bar joists, or to use a plywood or metal deck substrate. If you use a substrate, it seems that the sub-purlins would no longer be required.
I feel that the best course of action would be to use a metal deck diaphragm/substrate. It runs perpendicular to the joists and the metal roofing... perfect! However, what happens in the cavity space between the roof and the deck? It seems like you'd have to ventilate the space, both from a thermal and moisture standpoint. Do the standing seam clips simply screw into the deck? Has anyone ever been involved in using such a system? I also know that telling the owner/contractor that they need metal roofing plus metal deck is going to be a hard sell. This is a "cheap" unconditioned building. I need some good advice.
I feel that the best course of action would be to use a metal deck diaphragm/substrate. It runs perpendicular to the joists and the metal roofing... perfect! However, what happens in the cavity space between the roof and the deck? It seems like you'd have to ventilate the space, both from a thermal and moisture standpoint. Do the standing seam clips simply screw into the deck? Has anyone ever been involved in using such a system? I also know that telling the owner/contractor that they need metal roofing plus metal deck is going to be a hard sell. This is a "cheap" unconditioned building. I need some good advice.






RE: Standing Seam Metal Roof On A Bar Joist Roof
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Standing Seam Metal Roof On A Bar Joist Roof
RE: Standing Seam Metal Roof On A Bar Joist Roof
XR250 did something similar recently where the roofing was able to be the diaphragm: Link. PBR roofing or something. Perhaps you could steer your client in that direction.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Standing Seam Metal Roof On A Bar Joist Roof
Several of the metal roof system manufacturers have systems that will do what you need. Be careful with which materials you specify (are you near the ocean? Do you have high uplift resistance requirements?). Tall clips with long panels don't perform well over the long term. I have investigated fatigue failure of such clips just from thermal cycling. Also be concerned with pull-out and pull-over strength of fasteners when fastening into metal decking.
RE: Standing Seam Metal Roof On A Bar Joist Roof
RE: Standing Seam Metal Roof On A Bar Joist Roof
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Standing Seam Metal Roof On A Bar Joist Roof
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Standing Seam Metal Roof On A Bar Joist Roof
RE: Standing Seam Metal Roof On A Bar Joist Roof
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Standing Seam Metal Roof On A Bar Joist Roof
RE: Standing Seam Metal Roof On A Bar Joist Roof
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Standing Seam Metal Roof On A Bar Joist Roof
Another curious thought about the Vulcraft publication. Every joist & joist girder bay, by itself, has no internal diaphragm, yet somehow transfers lateral loads to the bracing/column lines. Are the joists to be considered braced only at the bridging lines?
Again, I basically have a single bay building, and my single bay isn't magically OK internally like all the bays in the Vulcraft publication... not much help!
Thanks for the bracing concept KootK.
RE: Standing Seam Metal Roof On A Bar Joist Roof
I haven't read through it in a while but I believe that all of the examples in the Vulcraft publication are situation where you still have a steel deck but it's capacity is augmented with the strap bracing. So, in those scenarios, I suspect that the deck is being used to brace the joists and transfer their contribution to lateral load out to the strap bracing system.
To stabilize the system, I'd think that you'd need:
1) A strap bracing system like those we've been discussing and;
2) The ability to count on your sub purlins to brace your joists and move roof seismic mass around.
I'm not sure that I've ever seen on OWSJ system that had no deck diaphragm whatsoever. This may be why.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Standing Seam Metal Roof On A Bar Joist Roof
RE: Standing Seam Metal Roof On A Bar Joist Roof
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.