Snow Drift on Adjacent Building with Separation

[rabroke]

I have a new, taller building being constructed next to an existing building with about a one foot separation. I know I need to check for snow drift on the low roof. I am using ASCE 7-05 for the drift, and due to the separation I can reduce the drift loads on the lower rood according to section 7.7.2. My question is, this makes sense for leeward drift for the snow blowing off the higher roof. But with the separation, does windward drift need to be checked? It seems to me that the snow would simply blow off the low roof into the gap. Any thoughts on this?

 

[ameyerrenke]

The snow can very easily dam up to cover a 1' gap.

 

[structSU10]

I have always seen drift accumulation illustrated with a wind current that folds up as it hits whatever obstruction that causes the windward drifting. I would imagine, with the same thing taking place, that a nice drift will stiff accumulate even being offset from the obstruction. I would imagine that leeward drift will control unless the low roof has a much larger fetch length, due to the 0.75 factor that can be applied to windward drifts.

 

[msquared48]

Sounds like a cornice situation to me.

Mike McCann
MMC Engineering