No self-respecting self sufficiency enthusiast should be without a polytunnel for some amped up veggie growing. Being able to produce your own veggies at home brings satisfaction for all sorts of reasons: providing for your family, true organic food, experimenting with stuff. This is assuming that one is able to get the stuff to grow. But that’s not our concern yet. Firstly we needed to build the tunnel and so we started some research into ways to make your own.
Having read through many diy descriptions, we opted to go for a design that uses polythene piping to make the arches. In the description we were following most closely, 2” diameter black polythene water pipe was used. For some reason we couldn’t source this so instead opted for ESB ducting, which comes in a nice 50m roll for about Euros80, and is widely available. Next up we needed some steel pipe that would be hammered into the ground to act as anchor points for the poly pipe arches. This steel pipe needs to fit inside the poly pipe. So we used 1” galvanised pipe which although it didn’t give a snug fit with the ducting, the result was still secure once the ducting was pushed down over the 3ft or so of steel above ground. We had hoped to make 7 arches at 4ft spacing, giving a 24ft long tunnel, but measuring the coiled ducting accurately proved to be difficult and so when it came to the last arch, we were short. So we have 6 arches at 4ft spacing for a 20ft long tunnel. The 7.5 meter arch span gave us an 11ft wide tunnel with a good high headspace (8.5ft).That’s still a lot of room for veggies (if they grow)! You’ll notice the sloping end wall at one end. That was simply an effort to add a little more floor area inside without the additional arch.
We visited some neighbors who are polytunnel pro’s to get their advice and experience.It seems that good ventilation is very important to get right. we were told It can be helped by ensuring you have a tall tunnel (with openings at either end). Hence the 8.5 ft height. The plan was to have a regular half door at one end, top half to be left open as a vent. While the other end was to have a tiltable vent or similar area. You can see the size of this vent are in the lower end in the images above. Hopefully this would be enough.
Next we went with some 4×2 pressure treated timber to use for the base rail to which the polythene would be attached as well as for the end structures to form the door and vents. Some 2×1 lengths were used to link the arches together and add rigidity to the structure. It seems that used scaffold boards are a nice and cheap way to do the base rail and provide a large area to attach the polythene too, but try as we could we weren’t able to find a local source at a reasonable price. It seems that many people are finding many uses for the surplus of scaffold boards that used to be around, and so they are now becoming a much sought after commodity for diy projects. An alternate design to the use of timber baserails, is to dig a trench all around the tunnel and bury the end of the polythene under a 1ft depth of soil. With the recent dry weather we’d been having, we figured this would be back breaking so at additional expense and less ideally we went with new 4×2 lengths.
While the structure was still being built….it is taking a while as there seems to be so much other stuff going on now with the fine summer weather…we ordered the polythene cover online from this company (www.polytunnelsdirect.ie).
An 11m by 8.75m section of 800g material we were told would be ample for our needs. We also ordered some heat tape, which is recommended for areas where the polythene touches metal or anything rough. The metal will get hot and damage the integrity of the polythene over time while any rough areas will obviously cause risk of tearing.The order arrived within a few days and is sitting waiting…
Our materials costs were as follows:
Steel pipe sections to hold up red pipe arches = €60
red ducting :€88
Timber (4x2s (10) + 2x1s (10)) = €140
polythene + heat tape = €170
total = €460;
Its a little more than I had expected for such a structure. While we are estimating that an equivalent kit purchased and delivered would cost at least twice that amount which is somewhat consoling, the labour time involved in building this so far has been significant. However there is plenty of satisfaction in taking on projects such as this yourself if you have the time to spend on it, so factoring in financial and time costs, is it still worth it?
We hope to have at least the structure completed by the next blog update, even if the growing hasn’t kicked off. There is a healthy crop of tomatoes sitting in pots waiting for their new home and a chance to thrive in our new tunnel so time is becoming of the essence. We are a little late for this years growing season, but hope to get some growing use from the tunnel this year.
Is the ESB ducting the same as the water polypipe, i.e MDPE? I’ve seen a lot of similar structures being built on American sites with PVC pipe, and apparently, that’s not a good product to use, because it can damage the plastic film. The PVC (polyvinyl chloride) gives off tiny amount of chlorine gas, especially in hot weather , which reacts with the standard polyethylene greenhouse film, causing it to cloud over and eventually causing holes (even if it’s UV-stabilised). MDPE (medium-density polyethylene), being made basically of the same stuff as the film, doesn’t cause the same problem.
Thanks for getting in touch.
The ESB ducting that we used is MDPE (PE80) material, which as you say is better to have in contact with the plastic film typically sold for polytunnels.
Ours has only been in place a year now, but there is no sign of any interaction between the two materials as I was hoping.