Snow Drift on Canopies
Snow Drift on Canopies
(OP)
I have a canopy that projects out 5 feet from the building. The roof of the building is flat and is 30 above the canopy. I considered windward drift which puts me at a maximum drift of 35psf. I don't think i should have to design for leeward drift, but i am looking for some hard evidence that states i do not. I don't see snow blowing off a roof 30 feet above and drifting onto a 5ft canopy. (Leeward drift calculation gives 70psf of snow max). Code is very limited on canopy loads. Is there any documentation that if the roof elevation change is X feet or greater you do not have to consider leeward drift?






RE: Snow Drift on Canopies
The code is silent in terms of a high vertical differential serving as a cutoff - if I remember the code right (too lazy right now to look it up).
RE: Snow Drift on Canopies
RE: Snow Drift on Canopies
RE: Snow Drift on Canopies
DaveAtkins
RE: Snow Drift on Canopies
RE: Snow Drift on Canopies
RE: Snow Drift on Canopies
How about the rest of you? Do you think a canopy qualifies as a "marquee"?
The Code defines a marquee as "a permanent roofed structure attached to and supported by the building and that projects into the public right-of-way."
DaveAtkins
RE: Snow Drift on Canopies
Interesting. That definition of 'marquee' would seem to fit a canopy if it extended out over a sidewalk or other public right-of-way.
I have always used IBC Table 1607.1, Item 30, 'Awnings and Canopies' for the minimum, non-snow, load on an entry canopy. But I can see your point if the canopy is over a sidewalk.
RE: Snow Drift on Canopies
The other day I saw some workers using a canopy as a stage area to set up their window washing platforms, etc. They had a few sheets of plywood protecting the canopy, the platform, a whole bunch of workers, and other equipment up there. I went back and asked the engineer who designed it, if he used 75psf and told him what I saw.
We do however reduce the load for a deflection check based on engineering judgement and material on the canopy.
RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke
RE: Snow Drift on Canopies
I can see the need for the Marquee loading on something that has a parapet (like a marquee would have or its sign) over an entrance. For flat roofs, I don't see the minimum 75 psf. Just compute the drift and apply it.
RE: Snow Drift on Canopies
I saw in the latest IBC code revision proposals one requiring a 1000 pound point impact load for all exterior canopies with a restaurant/bar useage under 30 feet directly above. Above 30 feet to the 60 foot limit, the load increases proportionately to 2500 pounds. Above 60 feet, if you read this far, the april fool jumps, so there is no load requirement.
Mike McCann
MMC Engineering
RE: Snow Drift on Canopies
Ron
things looking any better?
RE: Snow Drift on Canopies
Not really. I have one house job I am working on that pays and three pro-bono jobs I am involved in for two friends and my religion. Excellent time for that, right?
One bright note though...I saw that the price of our house went up 3K in March where it had been steadily declining. I don't know whether to believe it or not. I guess time will tell.
Mike McCann
MMC Engineering
RE: Snow Drift on Canopies
I'm optimistic...it's headed back and will get there quicker than others anticipate. Fingers crossed.