Will the snow load drifting double up at corner ?

[struct6]

Hi Folks,

what I have is a sloped lower roof which is surrounded by higher roof area along the north and east side. I calculated the drift width and drift load which is 6 ft and 30 psf respectively. my question is will the drift load be doubled up at the north east corner ?

Thanks

 

[JAE]

It will intersect like a valley of a sloped roof.

 

[jimstructures]

Per ASCE 7 05 and earlier, NO. The drift does not double. I haven't reviewed ASCE 07 10 yet, but I haven't heard of a change in the snow drift requirements in that area. Just use the higher drift load into the corner and then the lower drift as you turn the inside corner.

Your judgement may require you to add some load if the steps are very high and the upper or lower roofs are long. But that is a judgement call not a code requirement.

I havn't reviewed the Washington state Structural Eng's Associations comments on snow for a while so they may also suggest bumping the load up.

Jim

 

[struct6]

jimstructures,

Please can you tell me the section in ASCE 7 05 where I can find that the loading need not be doubled. Thanks

 

[msquared48]

I can visualize a special situation where the load might be higher very locally due to an ice crust forming, then more blown snow on top of that from a 90 degree direction, so I agree with the valley shape of the load pattern.

Mike McCann
MMC Engineering
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