Snow Drift on Lower Roofs from multiple sides

[jeffhed]

I have a project I am working on with a lower roof that has higher roof on three sides. So I have run three drift calculations. The drifts all overlap each other. Typically I have looked at all of these drifts as one load case occurring at the same time. Is this correct? Or do I actually have three load cases where I look at it with drift from side A, drift from Side B and drift from Side C and take the worst case? I think it should be all at the same time but I haven't found any direction in ASCE 7 on how to deal with this. So I thought it wouldn't hurt to verify that I am not over applying the drift loads.

 

[BAretired]

Wind is unpredictable. It can change in direction overnight, pushing fresh snow in all directions before the old snow has had a chance to melt. Higher roofs on three sides means the snow has nowhere to go, so it stays on the low roof. The answer depends on the size of the roof and the differences in elevation, but this roof has a tendency to fill with snow because it is shielded on three sides. Conservatism is warranted, so consider all three cases simultaneously.

BA

 

[jayrod12]

This was discussed here,

thread507-471843

Take a gander in that thread and see if it gives you enough of an answer.

 

[jeffhed]

BAretired,
We are in agreement. This is what I have done in the past and was doing on this project. The loads were getting so high on this project (compared to what I normally deal with) that I started to wonder if I wasn't overkilling it. Thank you.

jayrod12,
Thank you for the link. There was some good information in there.