This isn’t actually about irrigating your polytunnel although I’ll elude that in another post. What I wanted to write about this morning was how I added polytunnel guttering so that I can harvest rainwater from mine. There are a number of systems that involve sticking tiny thin guttering onto the outside of the plastic but I needed something a bit more robust. I acquired one of those 1000l white HDPE water containers that having been thoroughly cleaned has been mounted at one end of the polytunnel. Unfortunately there isn’t always a way of knowing what was in the container originally and I know that there are some pretty unpleasant things in them sometimes, certainly things that you wouldn’t want to give to your plants so wash it well first.
What I decided was that I would erect a proper gutter to the outside of the frame and plastic and here is how I did it. To have something to mount the gutter to I fixed a 2″ x 1″ batton all the way down one side before I put the polythene cover on. Make sure that you have a drop of an inch or two at the end where the water is going to go so that the guttering can be lined up with it. This could easily be done retrospectively but you’d probably want to do it in smaller sections, just slip them in behind the lower vertical poles and slide them up before clamping them to the poles. I made a mistake at this point as I couldn’t find the right fixings, what I used were thin pipe saddle clips rather than the proper clamps that are supplied for polytunnel building. If you fit this after the plastic though you’ll need to use the saddle clips unless you’re happy to have the holes for the bolts in the outside skin as you won’t get them in from the inside.
Once this was in place and the skin was on it was a case of attaching the guttering making sure that it drops in the right direction. If you angled the wood then just line up with that otherwise you’ll need to have the fascia clips lower at the end where the water container is. There are twos sizes that are readily available, 112mm which is for houses and large buildings and 76mm which is for smaller sheds and perfect for this. The larger guttering is overkill unless you’re doing this on a commercial tunnel. You’ll have to screw thorough the cover here but it should all be so firmly fixed that no movement will cause a problem.
And lastly as there’s now a gap between the gutter and the skin you’ll need some way of getting the water into the channel. I did a little research here and came up with a good and working solution. You just need to tape a strip of polythene onto the cover above the gutter to create a flap that overlaps the gap. I used a roll of the tape that you use to repair holes in the polytunnel covers and it’s worked really well. One note here though is that the cover and polythene flap need to be really clean before you attach the tape, any dirt will cause problems later as the tape comes away. I cleaned the small bits that I was taping with isopropyl alcohol but most solvents that don’t dissolve polythene will do fine. Note that last bit about solvents that don’t dissolve polythene!!!
Et voila. We had a storm just after I put this up and on a 15’x20′ tunnel I got about 40l in just over 20 minutes, not bad I thought. Good luck if you do this but let me know if you’ve done it differently or have any improvements on this idea.