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Re: Snow Drift Loading

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Our Canadian Code has a slope factor which for normal roofs varies linearly from 1.0 for a 30 degree slope to 0 for a 70 degree slope. "Slippery" roofs get a factor of 1.0 for 15 degrees to 0 for 60 degrees. These factors are applied to the full snow load on the roof including drift. The snow is assumed to slide off the roof. Believe the UBC has a similar factor. The problem with sliding snow is that it will possibly a) tear off the fascia or gutter system, b) block entrances/exits or c) injure passers-by. You'll often see crickets or gables over entrances to direct snow away from the entrance or even anchor details on the roof to hold snow in place. If none of the above hazards  are a factor then the sloping roof could solve the problem. I believe that snow drifting to lower adjacent roofs applies to leeward wind conditions. The snow from the higher roof is blown off and drifts down to the lower roof in a roughly triangular distribution. So I'm not sure that simply matching the slope of the drift would work.
 
John MacLean
Pomeroy Engineering Ltd