Polytunnel Part 3 - Frame Construction Begins

Hello, and welcome back to part 3 in this series documenting the build of our First Tunnels polytunnel build.  So far, I've looked at preparing the ground for the new polytunnel and getting the anchor plates into their final position.  The next stage looks at starting to get the frame erected.  When I bought the tunnel, there were various things that I could have chosen as extras to add to the base build.  In the case of First Tunnels when it come to the metal elements, I had options of twin support braces and crops bars to consider.  Twin support braces are poles which run the length of the tunnel parallel to the ridge pole, but several feet lower down each side of the polytunnel frame.  As well as strengthening support for the frame, they also provide somewhere to be able to tie up crop supporting structure to.  However, in our instance, where the tunnel is only 6 foot wide, I couldn't really see the benefit that they would bring in a relatively small growing space.  But, what I did opt for were additional crop bars.  They are horizontal bars running just above head height across the width of the middle two hoops of the tunnel.  They provide addition support and strength to the overall structure, but also hanging and valuable storage space for those things only used during certain times of the year.

It's strongly advised to work in pairs when constructing the polytunnel, but truth be told, it is possible to complete large parts of the build solo.  Although it is of course useful to have someone else around to pass tools when you're up a ladder!

The first part of the frame construction looks at getting the 4 primary hoops in place and pushed down into the foundation tubes.  Constructing the hoops is relatively simple, just sliding them together like a set of tent poles.  But you then go one step further.  A bag of self drilling screws are also included in the fittings kit.  These are used to drill through the end of one pole and into the swaged end of the connecting pole, screwing tightly into place.  Once driven home, it means that the poles can not easily be pulled apart.  

Now, if all is well with the foundation tube positioning, each of the hoops will be square to one another, in line and the ridge will be level.  Left as they are though, they are still quite flimsy, so once they are in place, there are four braces to fit.  One in each corner connecting the end hoops to the neighbouring middle hoop.  Once these are in place, everything can be adjusted so all the hoops are exactly vertical, and bolted into position.

Hoops and braces in place, it was time to add the ridge pole.  Using a series of 4 clamps, the ridge pole joins together all the components of the hoops adding further strength and structure, again allowing you to ensure that all the hoops are vertical with little movement.

One snippet of advise mentioned in the instructions which I initially didn't take was the use of pilot holes when drilling the self drilling screws into place.  Do they work on their own without a pilot hole?  Well, yes they do, and all seems well when you are able to drill down onto poles when they are laid on the ground.  But I underestimated how tired my arms would get drilling them into place while standing on a ladder and putting the ridge pole into place.  Drilling a 3 mm pilot hole into the metal join first made such a big difference.  So much easier!  

One pleasant surprise for me when I was unboxing the delivery was the inclusion of 4 short metal tubes with flattened ends.  Through previous research and comparing tunnel options between other providers, I knew that they were additional storm braces.  For some reason, I had assumed that they were an optional extra with First Tunnels, and so hadn't intentionally selected them.  Whereas the end hoops of the diagonal braces between hoops, the middle two hoops could still theoretically be lifted and separated by wind when the tunnel cover is on.  To address this, these short tubes are attached above and below the join in the tubes and bolted into place using 'Q' clips.  Once they're on, the only way those hoops are lifting is if the ground anchors are pulled out with them!

The final stage for this section of the build was to fit the two crop bars on the middle poles.  Again, held in place by clips, and bolted in place horizontally.  They add further structural integrity to the middle hoops of the tunnel, and if I had chosen a longer tunnel with more middle hoops, then crop bars would have been supplied for each additional hoop.  Below, you can see the crop bars in place, and also the storm braces on the middle poles.

So, we reached the end of day 3 of the build.  In truth, not 3 full days, but half days.  As I said before though, with no hard and fast date that this has to be done by, I'm more than happy breaking the build down into smaller chunks.  The next stage of the build takes a break from happening at the plot as I take to the next stage of construction in the comfort of the back garden.

Thanks once again for reading and coming along on this allotment polytunnel construction process.  Until next time, happy growing!