how to fix polycarbonate panels in a greenhouse roof

[topsy]

HI,

I do so hope that someone can come up with a suggestion to help us fix our polycarbonate roof panels in place. We have struggled to keep them in place for some years now but matters are only getting worse with the continuous strong winds we have had this winter, waking up to find that one or two panels have been blown/ripped off the roof. The greenhouse is an Eden of around 50 years old and of course was never designed to take anything but traditional glass which was held in place by weak aluminium clips. The same clips are too weak for polycarbonate so we have bought some of Two West & Elliot's wire clips, the thicker ones, but they are not much better. We are getting too old to continue this game for much longer, so any sensible suggestions to keep these panels in place would be most welcome. We find it difficult to reach the topmost part of the polycarbonate sheet and that means there is a weakness and a liklihood that the sheet will continue to blow out. The obvious solution is a new greenhouse, but that is unlikely to happen and in the meantime many of my mesembs are getting watered so so frequently and yes they are the winter growers but even they do not want as much rain as they are getting.

Help.

Suzanne & Tony Mace

[Darren S]

I used to have cold frames glazed with polycarbonate and the tops were a devil for blowing out. I noticed that because they are light and flexible the flexing in the wind just wiggles them out from the clips.

In my case what I did was glue some narrow bracing strips of more rigid thick perspex to the inner face of the sheets at intervals. This gave a bit of extra weight and rigidity without blocking too much light.

[edds]

Could you swap the clips for the full length push in bar capping?

https://www.greenhousesrus.co.uk/produc ... r-capping/

Otherwise, Darren's idea of a strip halfway down each section and then putting a polycarbonate fixing screw through the centre of each sheet would keep each sheet secure.

I'm going to go and have a look at what clips I have on my polycarbonate roof as they have held secure so far...
Will report back in a few minutes!

[Chris L]

Sounds like it wants bracing. Maybe some batons fixed across like this ("photoshopped") image.
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I am sure a local handy person could cut some wooden batons to length and wedge them in for you.

[edds]

I've got 5 of G clips on each side of my 4mm polycarbonate roof.

I bought mine from Elloughton Greenhouses,
https://www.elloughton-greenhouses.co.u ... -p13219309

I've not had a single sheet pop out since doing this in early 2020 (though one obviously will later today now!)

[Stuart]

Replace the polycarbonate with glass, the advantages outweigh the disadvantages. The first 12ft of my 40ft greenhouse was made from a recycled section of Suzanne's old greenhouse way back in the last century, it's still got the same glass other than the odd roof pane that's been broken by a passing cat. Polycarbonate is far too lightweight and flexible to be an easy glass replacement. Maybe it might be of use if the glazing bars were redesigned but the only thing that seems to work is glass. I looked into replacing the panes the cat broke but there wasn't any polycarbonate thin enough to use instead of glass.

Stuart

Sorry Suzanne, that was a typo, didn't mean to spell your name rong.

[Paul D]

I wonder how well the aquarium-type silicone sealant would work on polycarbonate & aluminium? It's pretty tough, being designed to hold a lot of pressure when building aquaria, but designed for glass of course.

[edds]

I wonder how well the aquarium-type silicone sealant would work on polycarbonate & aluminium? It's pretty tough, being designed to hold a lot of pressure when building aquaria, but designed for glass of course.

Silicone (especially the aquarium grades which are very pure so nothing toxic can affect the fish) is not actually that adhesive to anything other than clean glass - it was one of the issues with metal framed aquarium if people used silicone instead of putty. It will come away from aluminium and polycarbonate pretty quickly.

I like my polycarbonate roof and am in no rush to go back to glass. Fitting end closure profiles (if you haven't already) will help stiffen the panels across too.

[Mike P]

Ii addition to the spring clips I use lengths of 6mm or so timber strips wedged under the lip of the glazing bar across the sheet and it works a treat to stop them being blown out. I find one per sheet is sufficient to prevent them being blown out.

[habanerocat]

I wonder how well the aquarium-type silicone sealant would work on polycarbonate & aluminium? It's pretty tough, being designed to hold a lot of pressure when building aquaria, but designed for glass of course.

I don't know anything about aquariums but my refurbished greenhouse (polycarbonate on painted aluminium) is held together with silicone. The silicone used needs to be low modulus and suitable for polycarbonate. I tried a few and found this one the best for my 4mm polycarbonate.

https://www.spcsupplies.com/products/si ... ade-300ml/
https://www.sealantsandtoolsdirect.co.u ... rrency=GBP

Take my advice and put a bead of silicon under the polycarbonate (plenty where your panes overlap) and then seal all round on the outside.
I didn't put enough on the first time and then had to do most of it again, which as pointed out is very difficult. My old green house is glass bonded with a single bead of silicone and has been fine for years. But again as pointed out glass is heavier than the polycarbonate so I think you really need to be more generous on the polycarbonate.