Roof Wind Pressures

[Deadblow]

Hello,
I am working on a structure that will get "over-build" trusses installed on top of a flat roof to create a look like a mansard roof. I am trying to determine my reaction forces for these trusses. I have calculated my wind loads but I'm not sure when to use roof uplift or pressure with wall pressure or suction. Please refer to the attachment. I would think that #1 and #4 of the attachment are the forces that I need to design for. Are #2 and/or #3 ever possible loading conditions?

Thank you for your input!

EIT

 

[JedClampett]

I'd definitely use all of those combinations. The outward wind cases are substantiated by wind tunnel testing. As the wind blows over the object, there's a low pressure zone formed which creates those pressures. As a matter of fact, you're approaching a parapet design, which has even higher wind cases.
In my opinion, if you're not sure, you should include it.

 

[Deadblow]

Jed,
Thanks for the quick response and the explanation. I agree and plan to check the design as a parapet also.

EIT