Snow Drift Accumulation with respect to RTU Spacing (ASCE 7 Guide to the Snow Load Provisions) 1

[FoxSE14]

Hello,

For those that own the ASCE 7-10 or ASCE 7-16 versions of the text "ASCE 7 Guide to the Snow Load Provisions"....do they illuminate any opinions/conclusions on the tendency for snow to accumulate between closely spaced RTUs? Similar to the "15 foot rule" is there any guidance/threshold for spacing at which one might assume drifting between multiple pieces of equipment can begin to occur?

Our situation is an array of 3' to 6' square RTUs, with each spaced at ~3' apart, sometimes less. The entire array of RTUs is ~35' long...of course we could throw drift on each side of the 35' swath of roof and sleep at night...not sure if the client will appreciate the added cost though. Issue at hand is I need to respond to this question from our client: "Well, we can move the units around. How far apart should we space them?"

Of course the answer I want to give them is: "If you space them X' apart, we don't have to consider snow drift around the units"

Thanks,
Fox

 

[straub46]

I have access to the 7-10 snow guide, and the only thing it mentions is elevating the units as mentioned in ASCE 7-10 C7.8. My rule of thumb is if the units are spaced further apart than they are wide, I don't worry about drift accumulating on the group. Part of that depends on what the site/wind conditions are, but I've always felt that's a pretty safe assumption.

Go Bucks!

 

[FoxSE14]

Thanks for the input. Surprised the code & commentary offer no guidance on this. Engineering judgement it shall be.

 

[structSU10]

I have email the author of that guide in the past for some guidance. He was quick to respond and gave good insight - it was prior to the updated provision for clearances and he told me what the new code was going to define. I can't seem to find his email address, however...

 

[FoxSE14]

Great idea, I'll see what I can dig up.