[Bernard]

Hello folks
Just made a sudden decision to replace my 6 x 6 greenhouse with a 6 x 8, in autumn.  I can just squeeze it in.
I see several Qs & As in the forum about polycarbonate but they don't quite answer my doubts -

Whilst I see one statement that 'polycarbonate is double skin', nevertheless it seems that it can also be single. Have I misunderstood?
It blocks UV radiation. Don't the plants need it?
Does the double skin reduce rapid heat loss under a clear night sky in winter?
Does anyone have any particular points against it?

I see the Palram brand is quite economical. Does anyone have anything against this?

Looking forward to some good advice...

[tode]

Hi Bernard.  Polycarbonate can be simple sheets or multi-wall, up to 16 layers, I believe.
The more layers it has, the better it insulates, the stronger it is, and of course the more expensive it is.

I put up a double-wall polycarb GH a couple of years ago, and am very satisfied: can keep it at about +7° in winter with no great difference in electricity bill. 

And it's virtually unbreakable (I splashed out and got polycarb roof + polycarb sides, because of breakage risk.

It must absorb a bit of UV, but then so does glass.  You'll have to shade in Summer anyway.

Just to give you an idea, on an overcast day in winter, I have a 6 or 7° difference between inside and outside.

You can get simple sheets of thin polycarb, which isn't expensive, but I believe that quite a few people have had problems with wind damage: the sheets just aren't rigid enough.

Good luck with project.

[mumofstig]

My g/house is single polycarb and the roof is double skin.

As Tode says the single skin is quite flexible and the wind used to pop the sheets out if it was very gusty I got round this by sealing the panes in and adding a few extra screws where required

If you can afford it I would go for the thicker panels

[tosca100]

We have a double polycarb lean-to. We lost a few panels only once last year (had it two) when we had real gale force winds and it is on our drive so a wind tunnel, only one panel had any damage. We've put loads of extra clips on it but we don't get winds like that often. Apart from that, we are very pleased with it and the toms and peppers are too!

[Bernard]

Thanks for the info folks. I think I will go for the double skin.
 My greenhouse site is reasonably sheltered from the wind. My old greenhouse was almost blown off its base shortly after installing it by a freak wind which blasted right through a holly bush, but that was near 20 years ago and it has never been repeated.

I hope that the extra space will allow me to grow something else besides tomatoes though I haven't yet thought what it will be. At the moment. 12 Gardeners' Delight plants completely fill the house. And better insulation should give me more versatility through winter.