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Polytunnel construction is very basic in the methods and components used, apart from polythene.
The main elements could be sourced from discarded materials, depending on the size required.. The parts required are a method of securing the tunnel to a frame on the ground. This could be done by using 4x3 material in the case of a small polyframe for crops where you dont need walk in access, where access is gained by lifting the frame side. The next items are the hoops that support the plastic. These can be made from mdpe water scheme pipe 40- 50m mm upwards. It has a 5 mm hard wall, that will happilly take the cross supports of 2x1 laths, that also stop end racking, collapse form excessive wind..

If you are lucky enough to get steel hoops from a discarded tunnel, then its really a question of anchoring them into the ground, and covering with plastic. You can hammer in short lengths of piping, slightly larger than the hoop diameter, so that you get a male/female fit when you position the pipes.

In the cad drawing, the yellow and green parts , are the ground support frame, they grey curved parts are the hoops, and the blue parts , are the joining laths for the hoops. Of course depending on size, some parts may vary slightly, but this is basically the methods of simple polytunnel construction. Even constructing your own tunnel from a kit, will save you up to 500 euro in Ireland anyway.
If you are considering something like this, best to start a small frame maybe first to see how things go for you, and go fro there.

Chat you later,

gris..

Great stuff.

Do tunnels like this keep put insects (eg blackfly) or do they still find their way in?

You have to ventilate the tunnel and also allow pollinators in so yes unwelcome critters can get in too. It's not so much of an issue with the sort of stuff you'd grow in a polytunnel though. The main concern in a tunnel is with things like viruses. Tunnels provide ideal breeding grounds for them. So cleanliness is your friend. If you have fruiting stuff like toms in there for example, try to make sure that you don't let fallen fruit stay on the soil to rot.

dubmeup wrote:
In larger type frames, you,d normally verntilate through the end frames, as its easier to do at the end sections , as opposed to the top of the frame. Smaller cold frames can be easily raised to allow for venting ect. Or you could make square cold frames with a ventilated panel at the top that opens and closes when required. Such as this one made from 1 8x4 sheet of osb board, and 8 lengths of 2x2 roofing laths. As you can see in the picture, the top sildes forwards and backwards like a tol box lid. It measures about 16 feet long 4 feet wide and probably 4 feet 6 at the highest point.
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That's a really nice arrangement with those parallel hinges gris! I bet that works a treat!

dubmeup wrote:
Does what it says on the can , right enough. A couple of m12 x80,s , few washers, hey presto.

gris.