A textbook is attempting to convince me that the following figure:

Represents the generic zones for a Case B wind loading including roof overhangs based on the ASCE 7-10 Chapter 28, Part 2 (Enclosed Simple Diaphragm Low-Rise Buildings) procedure. This procedure addresses roof overhangs via footnote 8 on Figure 28.6-1:

"Where zone E or G falls on a roof overhang on the windward side of the building, use EOH and GOH f`or the pressure on the horizontal projection of the overhang. Overhangs on the leeward and side edges shall have the basic zone pressure applied."

I absolutely do not agree that the figure is a correct application of the Chapter 28, Part 2 wind loading provisions for Case B wind direction. Please see below for ASCE 7-10 Figure 28.6-1 Case B zoning. You may observe that zones H, E , A and C correspond, while zones G and F have been flipped.

I would like to know if the textbook is not applying the wind provisions properly, or if I am missing something in the code? Thanks.

Assuming ASCE 7-10 Figure 28.6-1 is correct and footnote 8 applies, I believe the following (edited) figure shows the correct distribution.

• Does the textbook display the coefficients for each of the areas as well? Maybe it also switched the coefficients for zones G and F, in which case it would just be a difference of nomenclature. Or does it say "these are the zones, but check the codes for the coefficients"? Also, check which version of the code is used by the book. Maybe it's an old version of the code which switched the zones.
– Wasabi
Feb 26, 2016 at 10:21
• Textbook is using ASCE 7-10. Note that this is the "Enclosed Simple Diaphragm Low-Rise Buildings Procedure" based on Chapter 28 Part 2. This procedure does not have any GCp coefficients (or anything like that) but rather refers the designer to the tables on Figure 28.6-1. There are no coefficients. Feb 26, 2016 at 15:21
• Would you mind sharing the title, author, and edition of the textbook this is from? Feb 26, 2016 at 17:48
• Hi William, this is from "Design of Wood Structures - ASD/LRFD, 7th Edition" by Donald Breyer. The figure is in the 2nd Chapter (I believe). Feb 26, 2016 at 17:57

I believe you are correct, the diagram in your book is incorrect in the way it has labeled Zones F and G. This is a bit of a stretch, but I think this may be related to/as a result of an error in Figure G6-5 of a publication released by ASCE called, Wind Loads, Guide to the Wind Loads Provisions of ASCE 7-10 by Mehta & Coulbourne and published by ASCE Press that I came across last month. This publication is an ASCE officially endorsed "How To" guide for ASCE7-10 wind provisions.

Figure G6-5 in this publication (below) is an attempt to replicate the image shown in Figure 28.6-1 of ASCE7-10 but was pretty horribly botched. You'll notice the same mistake with Zones F and G for Case B (called "Longitudinal in my book's figure) as well as some general drafting errors with the linework and arrow hatches.

There doesn't seem to be a published errata for this publication and when I attempted to contact ASCE about the figure last month I didn't get a response.

In addition to that point, I also think that there are at least three other errors in your figure as well.

1. Note 8 of Figure 28.6-1 of ASCE7-10 states (emphasis mine),

Where zone E or G falls on a roof overhang on the windward side of the building, use EOH and GOH for the pressure on the horizontal projection of the overhang. Overhangs on the leeward and side edges shall have the basic zones pressure applied.

Therefore, I think that the pressures on the overhangs on the side edges should be E and G instead of EOH and GOH as shown in your figure. The application of EOH and GOH on the windward side in your figure is correct.

2. There is also an error with the boundary line between EOH and GOH on the windward side. The boundary between EOH and GOH should project parallel to the axis of the building.

1. There is nothing in Figure 28.6-1 of ASCE7-10 that suggests the length of Zone E on the gable side of a structure is equal to $2a$ as implied in your figure. I believe that Zone E (and G) should extend all the way to the ridge as shown in Figure 28.6-1 of ASCE7-10. The width of Zone E is equal to $2a$ only on the eave side of the structure.
• Great information, thanks. I have edited the original question with a proposed correct distribution. Please let me know if you agree with the edit. Feb 27, 2016 at 5:08
• Yeah, it's looking pretty good to me. Note though that you also replaced your example for the original, wrong, figure with your revised correct one. Feb 27, 2016 at 13:51