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S-5 corrubracket engineering

I have a corrugated thru fastener roof. How does one determine the number of, or allowable weight per S-5? S-5 provides fastener pull out and shear data, but they seem to be silent on the allowable weight on the metal roofing itself, that is so it doesn't deform or crush. Is this a blind spot, or am I just not finding this data? Maybe it's assumed this will never be an issue?
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
I have a corrugated thru fastener roof. How does one determine the number of, or allowable weight per S-5? S-5 provides fastener pull out and shear data, but they seem to be silent on the allowable weight on the metal roofing itself, that is so it doesn't deform or crush. Is this a blind spot, or am I just not finding this data? Maybe it's assumed this will never be an issue?
It's not an issue for S-5 but rather for the roofing and the supports; S-5 has no control over how much the array weighs. You may need to get help from a structural engineer.
 
It's not an issue for S-5 but rather for the roofing and the supports; S-5 has no control over how much the array weighs. You may need to get help from a structural engineer.
Right, I had the same thought, that S-5! Doesn't supply the roofing, but come on this stuff is mostly all the same, and besides they supply pull out and shear which is certainly coordinated with the gauge of the roofing material.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
Right, I had the same thought, that S-5! Doesn't supply the roofing, but come on this stuff is mostly all the same, and besides they supply pull out and shear which is certainly coordinated with the gauge of the roofing material.
I think your main unaddressed concern is the dead weight loading on the roof support structure, which depends on joist spacing, purlin material, etc. which S-5 (understandably, IMO) does not want to address. Somebody else's problem.
 
I think your main unaddressed concern is the dead weight loading on the roof support structure, which depends on joist spacing, purlin material, etc. which S-5 (understandably, IMO) does not want to address. Somebody else's problem.
No not the roof loading, that has been approved by an engineer. I am talking about the point load of the array on the metal roofing ribs. It just seems to be a blind spot that nobody addresses.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
No not the roof loading, that has been approved by an engineer. I am talking about the point load of the array on the metal roofing ribs. It just seems to be a blind spot that nobody addresses.
Point loads should only be falling on structural elements below the roof deck, never between. Are you talking about continuous loads? Take a piece of Unistrut and lay it on the roof, it is a continuously loaded beam, but it is actually supported by the structure below the sheet metal.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
No not the roof loading, that has been approved by an engineer. I am talking about the point load of the array on the metal roofing ribs. It just seems to be a blind spot that nobody addresses.
Well for standing seam it's literally a blind spot, because you can't see the fasteners holding down the panelling. But with the Corrubracket aren't you screwing into the roof structure? If so why do you need to worry about loading in the roof metal? Also what are you then putting on top? Rail? Follow the rail manufacturers guidance?
 
Point loads should only be falling on structural elements below the roof deck, never between. Are you talking about continuous loads? Take a piece of Unistrut and lay it on the roof, it is a continuously loaded beam, but it is actually supported by the structure below the sheet metal.
Well for standing seam it's literally a blind spot, because you can't see the fasteners holding down the panelling. But with the Corrubracket aren't you screwing into the roof structure? If so why do you need to worry about loading in the roof metal? Also what are you then putting on top? Rail? Follow the rail manufacturers guidance?


Some of the clamps put the weight on the flat part of the metal roofing. If there is sheathing under, then yes that weight would be then immediately transferred to the sheathing. But if you don't have Sheathing, and don't put the brackets over purlins, then just the metal roofing will be taking the weight. But consider these, which put the weight on the rib, where there is no backing:

 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
Some of the clamps put the weight on the flat part of the metal roofing. If there is sheathing under, then yes that weight would be then immediately transferred to the sheathing. But if you don't have Sheathing, and don't put the brackets over purlins, then just the metal roofing will be taking the weight. But consider these, which put the weight on the rib, where there is no backing:

All this doesn't make any difference from my imagined S-5 perspective. S-5 provides the coupling between the roof membrane and the racking. They test, publish, and warranty their brackets' ability to resist being pulled off the roof, which is the only thing they have control over. The dead and point loading on the roof is determined by the weight of whatever the installer puts on them; that and the structural integrity of the roof system are not within S-5's purview.
 
All this doesn't make any difference from my imagined S-5 perspective. S-5 provides the coupling between the roof membrane and the racking. They test, publish, and warranty their brackets' ability to resist being pulled off the roof, which is the only thing they have control over. The dead and point loading on the roof is determined by the weight of whatever the installer puts on them; that and the structural integrity of the roof system are not within S-5's purview.
Again, I am talking about the interface between the S-5 and the roofing, and how much weight the rib it is attaching to can take before yielding. Seems like a very fundamental thing to test and provide a number for. Like I said, they do provide pull out and sheer which involve the yield strength of the roofing material so I don't buy that argument that they don't have control or it's out of their purview to provide acceptable load normal to the plane of the roof.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
Again, I am talking about the interface between the S-5 and the roofing, and how much weight the rib it is attaching to can take before yielding. Seems like a very fundamental thing to test and provide a number for. Like I said, they do provide pull out and sheer which involve the yield strength of the roofing material so I don't buy that argument that they don't have control or it's out of their purview to provide acceptable load normal to the plane of the roof.
Are you talking about how much weight you can put on an S-5 clamp before the clamp itself collapses? I'm pretty sure that would be such a high value as to be pretty much meaningless in a normal analysis. S-5 does not warranty anything but the clamps themselves and their ability to resist being pulled off the roof. The integrity of the roof system itself is not their problem, nor should it be. You are tilting at a windmill here; their policy is not likely to change.

When I was doing commercial array designs on standing seam roofs for a PV company, we had a structural engineer look at every job to validate our clip count, spacing, rail span, wind loading, etc. based on the type, orientation, and condition of the roof in question. The pullout strength of individual clips is a different analysis from the wind loading of an entire array; S-5 does not warranty total wind loading, either.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Again, I am talking about the interface between the S-5 and the roofing, and how much weight the rib it is attaching to can take before yielding.
In addition to depending on roof material and thickness, this is going to depend on the rib and sheet geometry, as well as the locations where the panel is fastened to the roof framing. In other words, this is a global question.

Like I said, they do provide pull out and sheer which involve the yield strength of the roofing material
Yes, but this is a local question which just depends on the roof material and thickness. I don't have access to the testing reports, but I expect the tests are done with a fairly small sample of roof material that is clamped on its perimeter.

Cheers, Wayne
 
Ok well seems like I am in the minority here thinking they should supply these values. I guess we'll just have to agree to disagree. This would not be rocket science to provide. This is industry standard stuff, there are only a few different profiles and gauges for through fastener roofing, and they're clearly taking the roofing material specifics into account anyway with their pull out values. Do you really think their pull out values are based on the tensile strength of the screw LOL.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
Ok well seems like I am in the minority here thinking they should supply these values. I guess we'll just have to agree to disagree. This would not be rocket science to provide. This is industry standard stuff, there are only a few different profiles and gauges for through fastener roofing, and they're clearly taking the roofing material specifics into account anyway with their pull out values. Do you really think their pull out values are based on the tensile strength of the screw LOL.
As far as I can see you are in a minority of one. Have you looked at any of the S-5 pullout tables? Yes, of course, they consider the roofing material and show different numbers. What you are suggesting, however, is that S-5's warranty should cover factors over which they have no control. Get a structural engineer; that's what they do.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I agree with ggunn. For example if I'm designing a system with Ironridge or Unirac rail and flashings, those companies give guidance on rail spans and such based on the pullout of the lag screws from solid wood rafters. They don't address the issue of whether the rafters are overspanned, which depends on the rafter size and spacing and where they are supported, things the rack manufacturer can't reasonably assume. What you're asking after here seems to be the equivalent of the latter. The point-load withstanding strength of the corrugated metal depends not just on its thickness and form (which may vary itself) but also on how far a distance it spans between being supported underneath. You need someone besides the S-5! to do those calcs for the particular building.
 
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