With the help of the Community Supported Agriculture members, we raised out first polytunnel on the 16th and 17th April 2011. This page has a lot of pictures from this, which may be of help to picture constructing your first polytunnel. We really struggled to picture how to raise the polytunnel despite having instructions and The Polytunnel Handbook.
This page is therefore picture-heavy 🙂
We start off with the polytunnel frame. Our one was from Northern Polytunnels, and it was secondhand so it came a a lorry-load of components. Like all good building works from prefabricated bits, it was good to lay them components out in groups of similar parts. The hoops are made of one half with a swaged end fitting into another half with an unswaged end. Bars are pounded into the ground and the ends of the hoops fit onto those. You can go full DIY and use rebar and blue plastic water pipe but we went the secondhand route. The Polytunnel handbook gives you some idea of the alternatives, however we didn’t find the text as clear as we would have liked it in parts. These instructions from Polythene One are what we mainly relied on.
We started off with the polytunnel frame which had been constructed beforehand, treating the parts as a large jigsaw. Tom from Canalside had taken a look at the frame when he visited us a fortnight ago just to check that we had the basics right and hadn’t done anything too daft with it.
We were constrained on the left-hand side by the onions planted there, as a tip for other polytunnel builders if you can arrange to have as much space either side of the polytunnel as about half the width that is all a good thing. It lets you dig the trenches either side and not have to barrow the soil back and forth. It’s also easier to be able to lay the polythene along the side when it comes to that.
You want a day which is warm and has little wind, it was about 5mph on the 16th. The day could have been warmer, which makes handling the polytunnel film easier and lets you get it tensioned easier, but it all worked out okay. As you can see not that many people felt the need to wear coats.
The first thing that needs to happen is a trench needs to be dug parallel to the long sides of the polytunnel, and a little bit away. the skin will be run into this, it comes a little bit away from the straight parts of the hoops. The trench is extended round the front, and angled inwards to meet the door posts – the PDF instructions have more detail.
The plastic film is unrolled and laid alongside the polytunnel. On ours it matters which side goes up, as the film is UV stabilised on one side only. So you want to read the instructions from your supplier and get this right if it matters which way up it is. If your ordered an excess to be able to do the door, then this is the point where you can trim it off, we hoped to get ours out of the spare cut out of the ends, so no need to trim anything off for the door
You then need to have a bit of help with several people pulling the plastic film up and over the frame
You don’t want anyone left inside. Then comes the time to make the first cut over the door, after you have made sure that you have an even amount of plastic on either side and front and back.
You’re committed now – the first cut is made at the top of the doorway. A flap of the polytunnel skin is then rolled up onto a batten of 1 × ½ × 12" wood to anchor it.You then go to the other end to tension the polytunnel skin – you have ot get this right, and it means pulling really hard!
You then anchor this with another batten in the same way as the other end
You then pull in the film over the doorway, pleating the film to take out the curvature of the frame ends. It’s important to have the pleats folded such that water doesn’t collect in them, otherwise it will get skanky and green over time. You do over the doorway and about a third down the sides, before starting to tension the sides.
you do that by infilling the earth from the trench to sandwich the film and put weight on it, starting with the middle panels of the polytunnel and working your way along to the door. You have to grab the end of the film and pull hard to shift the earth and get enough tension on the film, before treading it in.
The whole thing starts to take shape, and is not reasonably secure against gusts and rain, so it is time to have a little celebration.
There is still some detailed work to be done around the doorways, check and double check the hotspot tape is present and there is no bare metal against the film.