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The Greenhouse has been my labor of love this winter. It as you can see is actually a hybrid polytunnel and greenhouse. Every last bit of the design has been deliberate – though it may not look it at first. My major goals were:

  • To withstand the incredibly high winds in this exposed coastal location.
  • To retain heat, a problem with greenhouses and I believe polytunnels.
  • To be UV resistant.
  • To be large enough to have two parallel beds and staging.

I wind-proofed this design by hammering 70cm 6′ stakes into the ground and then connecting them at the base with heavy 8″ boards. The roof is then a triple blue water-pipe polytunnel using extra thick (1000 gauge) UV resistant polythene. The sides are twin walled UV resistant polycarbonate sheets joined with polytunnel repair tape.

The excellent thermal characteristics come from the polycarbonate which is almost as good as glass for trapping sunlight and better than glass for holding in the heat (better insulator). The 1000 gauge PVC is thick enough that it holds in the heat well. Though I am considering lining the room with fleece until winter is over to improve the heat retention further.

I’m also passively cooling/heating the greenhouse by increasing its thermal mass. I have achieved this by adding a slimline water butt and a large plastic black bin both filled with water. Water has a large thermal mass so it soaks up excess heat during the day and releases it during the night.

I have been up there in very high winds, the only thing that happens is that the roof polythene moves a tiny bit and the sides flex in and out. Considering that two of my plastic greenhouses blew outside the allotments I’m pretty chuffed.

And here’s what I purchased, the rest was recycled:

eBay

Polycarbonate Sheets

Heavy Duty Clear Plastic Sheeting

Amazon


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