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Gaz

Which polycarbonate sheet for greenhouse insulation

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Could anybody advise on what thickness of double wall polycarbonate sheet would be best to insulate the ceiling and walls of my greenhouse over winter. Greenhouse is 8' x 12' and I've fitted some tube heaters but need the insulation so they're not running all the time. I'd like to keep temperatures 10C min for my N maxima, Pings, Utrics & Droseras. VFT's & Sarrs will be moved to a mini greenhouse where I'll let the temps go lower than that.

I'm in Derbyshire in the middle UK so winters can go down to -5C or so, occasionally a bit lower (2010 being the exception at about -20,if that happens again I'll take the plants indoors). I've seen 10mm sheet and read on CPUK of people using 4mm but I've never used it before so I'm not sure of the pros and cons of each. Any recommendations would be appreciated.

I'll be removing the sheet from the walls once winter's over but might leave the ceiling sheets in place to provide a bit of shading (semi-opaque sheet for this part).

Thanks

Gaz

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If i were heating a greenhouse I would replace it all with laminated glass . It's made from two sheets of 3mm glass bonded together .

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I managed to fit in 6mm twinwall polycarbonate rather neatly on the inside of the glass, giving a triple glazed effect and leave it up all year. Its a lot neater than using bubblewrap and lasts a lot longer so not neccesarily more expensive in the long run. 2 inch polystyrene to a height of 3 feet around the bottom as well, very cheap effective insulation and no real impact on light levels.

10 mm would be better than 6mm, i just found 6mm clipped into place very neatly.

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Gaz,

I have used 10mm but it is not so easy to use. the secret is to seal every gap to make things airtight, as i said not easy with polycarb.

I would have to agree that horticulture grade (large) bubble is very good and probably the easiest and cheapest method. U-values of bubblewrap are quite good. and it will last a few years.

If you stretch a wire from gable ends below the ridge and at the eves, you can run a single length of bubblewrap from floor, up and over and back to floor to make a tent inside the greenhouse, seal joints with clear tape. also consider a bubblewrap curtain across to reduce the volume you need to heat.

I don't think tube heaters will keep up, a fan heater would be better, but a volume reduction would be a massive help.

If you visit "LIV supplies" online. they will supply cut to size sheets of polycarb at very good prices, and they tape up the ends too. Measure up accurately and allow 3mm/M expansion. I would use clear not opaque.

Hope this helps.

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Thanks for all the advice guys, you've given me quite a bit to think about. I thought about bubble wrap, but last time I tried it in a smaller greenhouse I got in a bit of a tangle and it never seemed quite right so (for personal reasons) I thought something more rigid would suite me better.

There's a lot of sense in what you all say and I like Dicon's idea of reducing the volume by hanging a bubble wrap curtain. So I think I'm going to give the 10mm twinwall a go with a bubble curtain splitting the gh down the middle. I've got 3 x double 5 foot tube heaters (at 80w/foot) and as Dicon also suggested a fan heater in reserve in case they can't keep up....just won't have to let the wife see the electricity bill for a while or there could be trouble :)

Thanks again

Gaz

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