Snow Drift Loads on Roof Depression
Snow Drift Loads on Roof Depression
(OP)
I was wondering what the common practice was for determining snow drift loads on a roof depression. If you have a 3' deep trough around the egde of your roof that is surrounded by a parapet wall, I would think that more snow could build up in the trough than the amount calculated with the standard drifting equations. I suppose the highly conservative approach would be to assume the trough fills with snow to the level of the roof, then add the usual drifting load on top, but I didn't know if there are allowances in the code to be a little more efficient than this.






RE: Snow Drift Loads on Roof Depression
RE: Snow Drift Loads on Roof Depression
1) with unlimited snow available to contribute to drift, I expect that the trough would fill up first then drift would deposit against the parapet in the usual way until a snow ramp formed that was gradual enough to prevent additional snow deposit.
2) with limited snow available to contribute to drift, I would expect the trough to fill first then drift of the usual profile would accumulate such the volume of drifted snow would equal the volume of snow available less the snow in the trough.
So I guess that my answer would be that I'd go with the conservative answer (1) for a large roof and perhaps a less conservative answer (2) for a small roof. That being said, I have no non-arbitrary basis for distinguishing between a large roof and a small one.
I also wonder if a wind parallel to the trough could fill it after which wind perpendicular to the trough would superimpose drift. Perhaps that scenario is already built into the ASCE provisions.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Snow Drift Loads on Roof Depression