snow load on roofs - Page 3 - Fiberglass RV


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Old 02-13-2014, 06:54 PM   #29
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You certainly can't increase the total weight of a given volume of snow by melting it. Carol may have and Francesca may have but God bless the child who knows this ain't so (you know who you are). Of course the residue of a month or two of snowfalls and freezing rain may present as a depth on the roof not much greater and in some cases less than the first powpow of the season.

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Old 02-13-2014, 08:54 PM   #30
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You certainly can't increase the total weight of a given volume of snow by melting it. Carol may have and Francesca may have but God bless the child who knows this ain't so (you know who you are).

jack

Say what??????

Please take a moment to review my posts on the subject, quoted below...no skimming this time, please...


First I said:
Quote:
Originally Posted by Francesca Knowles View Post

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.
Next, my response to Carol's assertion below:

Quote:
Originally Posted by Carol H View Post
.. snip... my comment was in response to your general comment...that although snow does increase in density its "total load" doesn't increase, which isn't correct.
Quote:
Originally Posted by Francesca Knowles View Post
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.
...Well?
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Old 02-13-2014, 09:25 PM   #31
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I'll make this easy. You win. "Load" is not a unit of weight so maybe it's offsetting penalties. Who cares?

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Old 02-13-2014, 09:49 PM   #32
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Originally Posted by rabbit View Post
You certainly can't increase the total weight of a given volume of snow by melting it. Carol may have

jack
With all due respect Jack I am going to suggest that you re read my post 10 which was the point I was attempting to make - the snows water content can increase and the weight goes up - doesn't need to melt or an increase in snow volume to happen.
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Old 02-13-2014, 10:31 PM   #33
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anyone got any popcorn?……...
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Old 02-14-2014, 07:12 AM   #34
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F=mA

If 12" of snow compacts to 8", no melting, no evaporation, despite the change in density there is no change in mass. Unless the acceleration due to gravity changes , the force (weight) is constant. If you could weigh the snow then melt it and weigh the water, you'll get the same value. Raz
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Old 02-14-2014, 07:22 AM   #35
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Originally Posted by Carol H View Post
With all due respect Jack I am going to suggest that you re read my post 10 which was the point I was attempting to make - the snows water content can increase and the weight goes up - doesn't need to melt or an increase in snow volume to happen.
NO! NO! NO! NO!


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Old 02-14-2014, 09:37 AM   #36
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LOL I give up!
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Old 02-14-2014, 09:54 AM   #37
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WOW !!!!! That Reagan pic is great !! I will remove the snow as soon as I can get to it. If it caves in that will be a tragedy but I do have insurance, paid a year in advance.
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Old 02-14-2014, 10:03 AM   #38
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Originally Posted by Carol H View Post
With all due respect Jack I am going to suggest that you re read my post 10 which was the point I was attempting to make - the snows water content can increase and the weight goes up - doesn't need to melt or an increase in snow volume to happen.
I went and read it. The DENSITY goes up. THere is NO new weight. You conveniently omitted the portion that talks about WHY the density changes.

From your link:
Quote:
Once the snow is on the ground, it will settle under its own weight (largely due to differential evaporation) until its density is approximately 30% of water. Increases in density above this initial compression occur primarily by melting and refreezing, caused by temperatures above freezing or by direct solar radiation. In colder climates, snow lies on the ground all winter. By late spring, snow densities typically reach a maximum of 50% of water.[39
So, again, the total weight does NOT go up, just the density increases
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Old 02-14-2014, 11:04 AM   #39
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LOL - clearly I haven't done well at making what was my original intent of commenting on the topic of snow loads on roofs of fiberglass trailers.

My last attempt - promise! The weight and density of any square foot of snow is not consistent in weight! Its weight, density & ultimately the total load on the roof of a trailer depends on the % of water content of the snow, wether that be at the time it falls or through other environmental factors resulting in it compacting down. The weight and density of a foot of high water content snow on a square foot area of a roof will have a higher density & can and will outweigh a foot and a half of the light fluffy lower water content snow on the same square foot of roof.


Bottom line being no one can say oh there is only a foot of snow on my trailer and it was fine with that last year and believe it will be the same this year as the weight of a foot of snow and thus the total load on the roof can vary greatly. Simple as that.
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Old 02-14-2014, 11:45 AM   #40
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Yup, this has been entertaining. Who's on first?
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Old 02-14-2014, 12:07 PM   #41
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Quote:
Originally Posted by Craig Broughton View Post

Just trying to save a owner form some springtime grief, his trailer had full sunlight from the south and as the snow melts the load gets heavier.
Quote:
Originally Posted by Carol H View Post
Snow usually does become much heavier as it melts. As it melts the moisture content can/will increase thus making it much heavier even though it may look like less volume.
There is no increase in moisture as the snow compacts. While the amount of moisture per unit volume changes (increased density), the mass does not. The number of molecules is the same, they simply get closer together. Again F= mA. If the mass doesn't change and the acceleration due to gravity doesn't change, then the weight doesn't change.

If you have a kitchen or postal scale, weigh a container of snow. Let it melt and weigh it again. The puddle will weigh the same. Raz
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Old 02-14-2014, 12:43 PM   #42
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I reread the writes and I read the rewrites. This has led me to believe that we're all on the same roof, something that wasn't clear to me initially. I found Carol's #39 a prize winner for clarity. I apologize to Francesca and Carol for mistaking the content of their argument for that of whichever yahoo (you know who you are) introduced us to the amazing alchemical snow. Can I send you a nice bottle of Cupcake to say I'm sorry?

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