Components and Cladding Wind Pressures - Permeable Facade

I am in charge designing some supports for a facade.
In calcing the C&C wind loads per ASCE 7-05 Method 2, the question arose as to if I should be including +/- 0.18 for internal pressures.
The cladding is permeable so wind can get behind the panels and maybe create pressure behind the panel, but this is definitely not internal pressure.
I think I feel comfortable using +/-0.0 for my internal pressures and just using GCp in my wind load calcs.

See below:


Great question, it really made me think about the way I design my cladding systems.

My first thought was to go to ASCE 7-10 Chapter 30 commentary C30.1.5 which deals with air-permeable cladding. To summarize it states that the applied pressures across the assembly will vary drastically so using the net pressure (including the internal pressure) is recommended. However it does leave the door open saying the designer may used an alternate design methodology.

I personally would still use the internal pressure coefficient when designing my cladding elements.

Above is a snippet.