snow load on roofs - Page 2 - Fiberglass RV


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Old 02-11-2014, 03:38 PM   #15
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Wikipedia - Snow - (scroll down to Density) gives a far better explanation than I can give you for it.

Per Wiki new snow commonly has a density of around 8% of water. After settling on the ground it goes to approx. 30% water - by late spring it can be as much as 50% water - mostly caused by melting and refreezing.
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Old 02-11-2014, 03:40 PM   #16
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But where does the additional weight come from? Is the snow absorbing moisture from the air?
Only where the laws of physics don't apply.

The only way for snow to get "heavier" as it melts is for more snow or rain to fall on it, thus adding more water.

There may be an added danger to roofs as snow melts if it causes pooling somewhere on the roof, though.
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Old 02-12-2014, 09:41 AM   #17
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Carol, the snow gets more dense, yes. So a cubic foot of snow will weigh more than it did. But if you have a foot of snow fall on a roof, weigh it, and then weigh it 3 weeks later when it's melted/refrozen to 2-3 inches, it will not WEIGH more. There is no increase in MASS, just in density.
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Old 02-12-2014, 09:44 AM   #18
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Carol, the snow gets more dense, yes. So a cubic foot of snow will weigh more than it did. But if you have a foot of snow fall on a roof, weigh it, and then weigh it 3 weeks later when it's melted/refrozen to 2-3 inches, it will not WEIGH more. There is no increase in MASS, just in density.
Did you factor in the coefficient of vapour loss due to the applied solar energy upon the snow mass?
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Old 02-12-2014, 10:49 AM   #19
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Carol, the snow gets more dense, yes. So a cubic foot of snow will weigh more than it did. But if you have a foot of snow fall on a roof, weigh it, and then weigh it 3 weeks later when it's melted/refrozen to 2-3 inches, it will not WEIGH more. There is no increase in MASS, just in density.
Your correct when the snow has melted down 9" as you suggest above but my comment was in response to your general comment below that although snow does in crease in density its "total load" doesn't increase, which isn't correct.

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Huh? The density goes up, but the total load should stay the same or less, right? Or am I missing something?
Bottom line one can not look at their trailer and say I know its good for at least 1' of snow. no 1' of snow is created equal or weighs the same. To many variables.

In areas of frequent snow its not common to go 3 weeks without any new snow falling on another layer of old higher density snow - which can result in that 1' of snow on the roof weighing far more than the first seasonal 1' of snow fall. Also as I mentioned depending on the water content of that original 1' of snow there can be a great weight difference to what a cubic foot of it weighs to start with.

Bottom line is its good practice to remove snow from the roofs of fiberglass trailers and boats as they are just not built to withstand the roof loads created by snow
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Old 02-12-2014, 12:18 PM   #20
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Carol, no doubt that the foot of snow on a camper at the end of a season could weigh more than the foot of snow at the beginning of the season due to the bottom several inches having been partially melted and then new snow fallen on top of. BUT, my original response was in reference to Craig's statement:

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and as the snow melts the load gets heavier.
And this statement is NOT correct.

And yes, you're right, a foot of snow is NOT a foot of snow. I have no issue there. Just the way that Craig's statement is written looks to me as to say that snow GAINS mass as it melts.
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Old 02-12-2014, 12:50 PM   #21
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Your correct when the snow has melted down 9" as you suggest above but my comment was in response to your general comment below that although snow does in crease in density its "total load" doesn't increase, which isn't correct.
Yes, it is.
Density is a unit of measure and load is a unit of weight- if speaking of "totals", neither has any effect on the other.
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Old 02-12-2014, 12:53 PM   #22
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Old 02-12-2014, 01:24 PM   #23
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Old 02-12-2014, 01:50 PM   #24
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Old 02-12-2014, 04:55 PM   #25
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Snow loading of the roof...

...is the reason I was working my tail off last December to finish my Scamp shed. This picture was taken two days later, on 12/15/2013 (Central Vermont). It sure is very nice not to have to worry about pulling the snow from the Scamp after every storm.
And, to put it simply, a thousand pounds of snow is still going to be a thousand pounds, unless it melts, or more stuff falls. When we get a March rain after three feet of snow, that is when I head for the roof with a shovel.
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Old 02-13-2014, 04:01 PM   #26
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I think it's time to clear off the trailer !!!!!!!!!!! Tomorrow !!
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Old 02-13-2014, 04:42 PM   #27
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I think it's time to clear off the trailer !!!!!!!!!!! Tomorrow !!
If "tomorrow" doesn't get here quite in time, you may find this interesting reading:

Advice repairing caved in Scamp 13 roof



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Old 02-13-2014, 06:10 PM   #28
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I cleaned the snow off of my camper today three times...didn't want to know how much snow would it take to harm it. Just knew I had to do it. Got just shy of 2 feet of snow.
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