Weight of snow on greenhouse

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PLUMPUDDING
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Weight of snow on greenhouse

Postby PLUMPUDDING » Thu Dec 02, 2010 12:58 pm

My friend's greenhouse has collapsed under the weight of snow on the roof. It was an ordinary 8 x 10 ft aluminium one and 18 inches of snow was too much for it and the roof just buckled.

I've spent the last hour clearing most of the snow off my greenhouse just in case. I know a bit of snow can insulate it from the cold, but the weight of what I cleared off was huge.

So if you aren't sure how strong your greenhouse is it might be a good idea to remove at least some of the snow.
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Re: Weight of snow on greenhouse

Postby oldherbaceous » Thu Dec 02, 2010 8:23 pm

Evening Plumpudding, very sound advice.

I cheat and put the heater on high for ten minutes. :)
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Monika
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Re: Weight of snow on greenhouse

Postby Monika » Thu Dec 02, 2010 8:54 pm

Gosh, yes, Plumpudding, I will go out tomorrow and clear the snow off our ancient (albeit wooden) greenhouse. I left it on for insulation, but the weight is certainly a worry.
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alan refail
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Re: Weight of snow on greenhouse

Postby alan refail » Fri Dec 03, 2010 7:11 am

Hi PLUMPUDDING

I was intrigued by your friend's disaster. How much does snow weigh? According to most replies I can find on the 'net, depending on the consistency of the snow, it weighs between 7 and 15 pounds per cubic foot.

If my maths is right (it often isn't!), 18 inches of snow on that greenhouse could equate to between 840 and 1800 pounds of snow, or 380 and 820 kilos - i.e. anywhere between a third and three quarters of a tonne :!:
Poor greenhouse :( :(
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Re: Weight of snow on greenhouse

Postby Nature's Babe » Fri Dec 03, 2010 12:16 pm

Well just before it snowed I tented my broad beans with old greenhouse metal frame and environmesh stretched over it - wonder what the breaking strain of that is. :lol: Last year I used plastic hoops and mesh and the whole lot collapsed on the plants - so far so good.
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Re: Weight of snow on greenhouse

Postby Beryl » Fri Dec 03, 2010 2:50 pm

I've just been out to clear the snow from mine really to get a little light to all my over-wintered cuttings and to avoid any cracked glass - glad I did now.
A good reminder - thanks.

Beryl.
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Re: Weight of snow on greenhouse

Postby Monika » Fri Dec 03, 2010 8:37 pm

We had minus ten degrees in the greenhouse last night, but then the sun came out and the inner warmth obviously softened the snow on the roof, so it slid off the glass quite easily. Only the frame and the edges now still carry the remaining snow. And tonight it is likely to be far less cold (I hope).
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Re: Weight of snow on greenhouse

Postby Primrose » Fri Dec 03, 2010 9:25 pm

Will have to bear this in mind if we have any heavy snowfalls. We don't have a greenhouse but all along one side of our house we have a covered potting shed area which is roofed with corrugated see-through polythene which is now 30+ years old and very fragile. The only problem is that it extends right to our boundary fence with our next door neighbour and the only way of accessing it is via his garden. And he's away much of the time and we have no means of accessing his garden. It would be hugely frustrating if that happened and we couldn't do anything about it.

I'm surprised in a way that the sheer weight of snow on the greenhouse didn't cause it to fall away, but I guess once the temperature drops below zero it freezes solidly to the glass and can't then slip downwards.
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Re: Weight of snow on greenhouse

Postby Beryl » Fri Dec 03, 2010 9:50 pm

I might be wrong Primrose but I think it was the guttering on mine that stopped the snow sliding off. Ice and snow had built up to make a wedge. I did have to clear the guttering as well as sweep the snow off.

Beryl.
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Re: Weight of snow on greenhouse

Postby Johnboy » Sat Dec 04, 2010 9:20 am

Hi Natures Babe,
With the plastic tubing you used, was it 20mm blue water pipe?
I have found that 25mm is the minimum I would use which is considerably stronger and I always make a ridge of bamboo and put a few uprights secured (screwed) to the ridge. If you put the ridge inside the hoop and tie in then there is just enough room to get the upright clear of the hoops so as not to snag your covering whatever it may be. This means that the whole structure is rigid and quite strong. However I use 20mm water pipe as simple loops dotted about in my strawberry bed simply to support the netting and because they are only short they have only to bear the weight of the netting and only when the strawberries are an easy target to the birds. So I don't have enormously high loops over my strawberries which means the netting has therefore a wider span. By having a lower net I can cover three rows instead of two if you get what I mean!
I will admit that the only reason 20mm pipe was used was because I bought a 100M roll to find that it was unsuitable for purpose! I bought it at auction so it only cost me £12. (some years ago now)
JB.
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