Snow drift on very small lower roof
Snow drift on very small lower roof
(OP)
What is your opinion on a very long Lu and very tall upper roof, against a very small lower roof and in which the calculated drift width W ends up being a LOT larger than the lower roof width?
Would you then use the drift width W the same as the lower roof itself or would use a truncated snow drift shape? (Trapezoidal shape) Doing that would increase the snow drift load by a factor 6 or 7.
Would you then use the drift width W the same as the lower roof itself or would use a truncated snow drift shape? (Trapezoidal shape) Doing that would increase the snow drift load by a factor 6 or 7.






RE: Snow drift on very small lower roof
Mike McCann
MMC Engineering
RE: Snow drift on very small lower roof
DaveAtkins
RE: Snow drift on very small lower roof
RE: Snow drift on very small lower roof
RE: Snow drift on very small lower roof
RE: Snow drift on very small lower roof
Use the truncated drift.
RE: Snow drift on very small lower roof
Use the truncated shape. ASCE is very clear on this and I don't believe it's open to much interpretation.
RE: Snow drift on very small lower roof
Never, but never question engineer's judgement
RE: Snow drift on very small lower roof
RE: Snow drift on very small lower roof
Is there an angle of friction for the snow that you cna use to justify reducing the snow load?
RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke
RE: Snow drift on very small lower roof
Never, but never question engineer's judgement
RE: Snow drift on very small lower roof
RE: Snow drift on very small lower roof
RE: Snow drift on very small lower roof
RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke
RE: Snow drift on very small lower roof
Never, but never question engineer's judgement
RE: Snow drift on very small lower roof
RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke
RE: Snow drift on very small lower roof
RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke
RE: Snow drift on very small lower roof
Never, but never question engineer's judgement
RE: Snow drift on very small lower roof
I've seen small eyebrow canopies with piles of snow like that many times in the midwest.
The thing is, whether the snow piles up or not depends on a lot of factors (prevailing wind direction, wet vs. dry snow).
For some conditions, it might not ever occur (per miecz's experience stated above), but it can happen (I've seen it) and therefore the code requires you to account for it.
RE: Snow drift on very small lower roof
There is no real clear definition, but it does say canopy in the title. How could justify NOT using it? You can't just dismiss the fact that canopy is in the description of the LL required. Although marquees is by itself in the IBC LL Table. My boss has always made us design to 75 psf, and didn't really care for what the code also states in 1607.11.2.4 that Awnings and canopies shall be designed for uniform live load of 5 psf + snow and wind loads. Then in section 3105 and 3106 it tries to define a canopy, awning and marquee, but I think it just makes things worse.
But I actually called ICC and they couldn't answer me for how to define a canopy, awning and marquee.
RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke
RE: Snow drift on very small lower roof
Never, but never question engineer's judgement
RE: Snow drift on very small lower roof
RE: Snow drift on very small lower roof
ASCE7 commentary: "C7.8 ROOF PROJECTIONS
Drifts around penthouses, roof obstructions, and parapetwalls are
also of the "windward step" type because the length of the upper
roof is small or no upper roof exists. Solar panels, mechanical
equipment, parapet walls, and penthouses are examples of roof
projections that may cause "windward" drifts on the roof around
them."
Therefore, lower roof Lu applies and the 10 ft tall snow drift disappears...
RE: Snow drift on very small lower roof
RE: Snow drift on very small lower roof
Mike McCann
MMC Engineering
RE: Snow drift on very small lower roof
I agree, if the upper roof is steeply sloped. In this case, I got the feeling the op was dealing with a flat upper roof.