Peer-to-Peer Standards Exchange

I have recently noticed that more of the jobs I have been reviewing, where glass railings on the roof of a building have combined loads of roof and wall loading. I understand the concept behind designing the physical parapet in this manner, but I do not understand using the same loading for a railing that is attached on the interior side of the parapet. Because of the gaps in the glass as well as the gaps in the glass shoes that are attached to the wall, I don't see how the leeward and windward pressure stack. Has anyone else encountered issues similar to this? the designs of the glass railing on the roof have gone from 1/2" laminated tempered to 13/16" laminated tempered or even thicker. I have read through the ASCE 7 code, but any additional insight would be greatly appreciated.

thank you.

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Chris Zambrano A.M.ASCE
Structural Engineer
Carlstadt NJ
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This is how I typically design glass roof railings. Since they aren't explicitly addressed in the code, I've compared a few approaches and settled on parapets (with the rail functioning as an extension of the parapet height if it's attached to a parapet) as both the most similar condition that is explicitly addressed, and the most conservative of the potential options. I have seen one design where the glazing shoe for a rail was vertically offset from the roof surface and laterally offset from the parapet face by long (1'+) outriggers and I could see the argument for that case not needing roof suction to be considered, but I really rarely see detailing like that. 

Regarding the joints, for what I work on they're usually ≤1/2" on a 5' mod (<1% of the length) with the gaps between glazing shoe segments usually being much smaller. I'm not aware of a way to justify a reduction in wind load or that roof suction won't be present on the back surface because of these gaps, but I'd love to learn if you are!

This structuremag article might also be helpful https://www.structuremag.org/article/frequently-asked-wind-questions/

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Renn Henry, PE
Staff Engineer
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