ASCE7-02, 7.7.2 Adjacent Structures

[jheidt2543]

Could someone review this paragraph in ASCE7-02 and explain what they are trying to tell me? My confusion is with the "factor" in the last sentence, (20s)/20. To me that equals "s", but then what? Do you divide it into or subtract it from something???

The problem I am looking into is putting a new, taller addition next to an existing, lower roof building. What spacing is needed to ensure no snow drift load on the lower roof? In the old State of Wisconsin Building Code (I think it was adopted from the Canadian Code) they used a dimension of 15'. I want to design the new addition roof with a step in it, so the new roof adjacent to the existing roof is at the same elevation for a distance equal to "s" and then step up to full height.

 

[jheidt2543]

Anyone out there? I'm just wondering if my copy of the ASCE7-02 code is the only one with this misprint and I would like to confirm what the equation should be. I sent an e-mail to ASCE and haven't heard from them either! Is this just a trivial question that I don't see the answer to?

 

[aggman]

From my interpretation....The paragraph reads that if an adjacent structure is within 20 ft of a roof then the drift load is to be reduced by a factor (20*s)/20, where s is in feet. I take this to mean that is the structure is 5 feet away, you would take (20*5)/20 = 5, then reduce the drift load by 1/5.