ASCE 7-16 Ch 28: Part 1 vs Part 2 1

[keen_mentee]

Most of the project I do satisfies the requirement for part 2 (Enclosed simple diaphragm low-rise buildings). I am trying to understand part 1 (enclosed and partially enclosed low-rise buildings) of ASCE 7-16 chapter 28 and have some confusion. I would appreciate any insights on this matter.
1. For part 2, we have both the horizontal (zone D)and vertical (zone G) pressure zones for the roof. This will lead to a different horizontal and vertical pressure on the roof. For a few test data, these value are very different from each other. In one case, I got the vertical pressure to be three times higher than the horizontal pressure.
2. For part 1, we have an equation 28.3-1 that indicates the pressure coefficient GCpf to generate the pressure. However, there is no distinction between the horizontal or vertical coefficient on the roof.
3. Does this mean using part 2, we get the same Horizontal and vertical pressure for roof? Also, what direction is the pressure/force that is given by the eqn 28.3-1? Is the force horizontal, vertical or perpendicular to the roof surface?

Please help!

Thank you.

 

[DanKile]

For chapter 28 part 1, the wind pressures are perpendicular to the surface. The only case where it is not is the minimum wind pressure. Then it is 16psf to the wall and 8psf to the vertical projection of the roof.