# Weight of snow on roof increases as it melts??

11242 Views 11 Replies 11 Participants Last post by  SeniorSitizen
After a 30 inch snowfall here in WV last weekend, I had conversations with several neighbors who told me to shovel my roof.

(1) Their opinion: As the snow melts, it gets heavier which would add weight to the roof, and the roof could collapse.

(2) My opinion: They are incorrect. As the snow melts, the density of the snow increases but the volume of snow decreases. The total weight of snow on the roof remains the same. (Might even decrease as it sublimates from sunshine and/or melting snow runs into the gutters.)

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a pound of bricks or a pound of feathers..................now if it rains...snow is like a sponge and will hold the water and gain weight....as it melts and the water drips off, then weight will decrease...either way, I would try to unload the roof a bit of snow...
....as it sublimates...
Obviously a physics major.

You win.
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I've spent a good portion of the day trying to determine the dollar amount of government grant money I would need to study that over a 10 year period. The numbers are mind boggling for an old farm kid.
I seem to recall a similar puzzle about a truck driver with a load of birds crossing a bridge. The driver is overweight, so just before he crosses the bridge, he beats on the side of the truck to get the birds the fly around. Figures it will lighten the load.
Ayuh,.... I'd just be concerned whether a roof in WV is built to withstand a 30" snow load,..??..??

Even up here in the snow-belt, 30"s on the roof is time to drag out the roof rakes,....
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After a 30 inch snowfall here in WV last weekend, I had conversations with several neighbors who told me to shovel my roof.

(1) Their opinion: As the snow melts, it gets heavier which would add weight to the roof, and the roof could collapse.

(2) My opinion: They are incorrect. As the snow melts, the density of the snow increases but the volume of snow decreases. The total weight of snow on the roof remains the same. (Might even decrease as it sublimates from sunshine and/or melting snow runs into the gutters.)

I think you need to move. You're too smart for West Virginia.
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Hi goshen,
if you are in an area where that 30" is apt to stay for a month or so, then removing most of it when it is convenient is a lot better than in the middle of a rain storm. I just got an email from a friend in SC and his comment was "what snow", but I assume whatever he had was mostly gone.

It's your neighborhood and you have to judge whether it will melt away by itself or be a hazard to leave up there. You already know that melting in place does not increase the weight, but if it is above the design load, the longer it remains, the higher the risk. Up here in Maine we often get buildings that give way several days after a storm. The weight can be relentless.

Bud
Whatever you do, don't get up on top of your roof with a shovel. A sloped roof with snow on it is a slippery place to be, and you could slide off of it.

Phone around to see if you can RENT a roof rake. Roof rakes are meant to be used from the ground to pull the snow off the roof with a wide bladed tool that somewhat resembles a landscaping rake. Basically, you stand on the ground and use this very long tool to scrape the snow off your roof.

And you are correct. Snow doesn't get any heavier as it melts.
Agree that snow doesn't get heavier as it melts, but there is a difference based on the moisture content of the snow. A very dry snow can weigh as little as 3 lbs/ ft³, while a very wet snow can weigh as much as 20 lbs/ft³.

If you have a metal roof and no snow guards, be aware of a possible avalanche.
Whatever you do, don't get up on top of your roof with a shovel. A sloped roof with snow on it is a slippery place to be, and you could slide off of it.
Depending on the pitch and assuming asphalt shingles its actually pretty safe. That much snow ain't going anywhere in a hurry. I would have no hesitation on anything up to a 6/12 if there was 30 inches of snow on asphalt shingles.
Depending on the pitch and assuming asphalt shingles its actually pretty safe. That much snow ain't going anywhere in a hurry. I would have no hesitation on anything up to a 6/12 if there was 30 inches of snow on asphalt shingles.
I'd be afraid to get on a roof with less than 6/12 and rafters on 24"OC and 30" of wet snow for fear I would end up in the living room.:surprise::biggrin2:
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