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Re: GCpi=0?

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> From: "John Peterson" <jpeterson(--nospam--at)>

> I am investigating the wind loads imposed on a standing seam metal roof
> system that is attached to plywood substrate, which is connected to the
> structural metal roof decking.  I am considering the standing seam metal
> roof as a component and cladding per section of ASCE7-02 where
> the building height is less than 60 ft.  In reviewing Eq. 6-22, it seems
> that GCpi should be zero since the standing seam roofing will not be
> subjected to any internal pressures since the deck below, which resists the
> internal pressures, supports it.  Is my assumption of Gcpi = 0 correct?

Probably, for the metal panel design.

Where is the architect's air barrier? Will the air be able to pass from
under the panel to the exterior at any locations?

If the air can pass through the cracks between the plywood, or at other
details, you can have interior pressure beneath the metal panel. It will
be attenuated considerably by the resistance to flow of "small"
openings. So, interior G beneath the metal panel may be so low that the
internal pressure is trivial for the panel design.

On the other hand, the panel is supported. Assume the worst and add more
fastenings. I'll bet the cost is relatively small. WARNING: You may take
some flack for being an overly cautious, conservative, a**-protecting,
criminal ... I mean, engineer.

Paul Ransom, P. Eng.
Burlington, Ontario, Canada
<mailto:ad026(--nospam--at)> <>

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