Polytunnel Part 5 - Building and Fitting the Door Frames

G'day to you, and welcome to part 5 of this mini series looking at the construction of our First Tunnels polytunnel.  Progress this far has been great, and everything is turning out as well as can be expected.  In part 4, I covered building the doors to be used at each end of the polytunnel.  Now it's time to look at the construction and installation of the door frames.

The simplicity of the design and the build process makes what could be a complicated and frustrating part of it into a very straight forward and logical process.  Usually, if you were to fit new doors at home, you'd either need to be an talented DIY'er, or a carpenter in order to get that perfect fit, and shape the door to meet the shape of the frame.  All the doors I have hung in the past have usually needed a degree of woodwork doing on them to get them to fit properly.  A job that can't be rushed and one that could go very wrong proving to be expensive.

When it comes to the polytunnel construction though, the need for fine carpentry skills are easily dispensed with by a stroke of genius.  Instead of building the door to fit in the frame, you build the frame to fit around the door.  Starting with one of the doors laying flat, it's just a case of arranging the frame timbers around the door with a sufficient gap to allow for expansion in wet weather.  Again, as most of the timber comes in nominal lengths, there is only one cut to make for the lintel section, determined by the width of the door.  Very easy.  It's all held in place by a couple of long screws and secured further by using nail plates both sides of the join.

Once the timbers are in place, a piece of batten is nailed just below the bottom of the door.  This acts as a kind of door threshold when it's hung on the frame, but it also comes in very useful for another reason as will become evident.

Leaving the doors at home, I transported the frames up to the plot, and the job for the rest of the day was to hang the door frames onto the metal frame of the tunnel.  As our tunnel is on a soil base, I needed to dig a couple of holes for the frame to sit in.  Digging these holes a little deeper than the length of the timber sticking out at the bottom of the door frame meant that the batten acting as a threshold sits automatically at the correct height for the door frame and ensure there is enough room for the door to open and close.

The next step to hanging the frame is to make sure it is level across the lintel, the frame sides are vertical and that the whole door frame is central to the top of the end hoop of the tunnel.  Once all these factors are correct, the top end of the frames are marked so they can be cut down to size.

Then, it's just a question of offering the door frame back up to the tunnel frame, repeating the process of getting everything centre, level and vertical before securing it all into place with P clips.  The bottom of the frame was left slightly hanging which allowed me to manoeuvre it into position, up against a string line across the width of the tunnel.  Finally, backfilling the holes held the frame securely at the bottom.

Exactly the same process was used both ends of the tunnel and it was job done.  So far, I have still managed to complete all aspects of the build on my own, just taking my time, not rushing and paying close attention to the instruction and video.  Thankfully, we have good phone reception on the allotment, so streaming YouTube videos onsite is easy!  This element of the install wasn't all plain sailing.  There were certainly times while hanging the frames when I could have done with someone else to support the frame or hand up tools while I was on the step ladder, but with a combination of wedging tools between my knees, under my chin and ramming any other bits and bobs into my pockets, I got there in the end.

Finally, to round the day off, I took another tip from other people who have built polytunnels in the past.  We are getting close to the time where the cover will be put on the tunnel, and any chance of getting bulky materials into the tunnel via the wheelbarrow will be lost.  With that in mind, I got 4 wheelbarrows of digestate compost from the allotment supply pile, and barrowed it into the middle of the tunnel. Eventually, I will have two beds divided by a central path running through the tunnel.  The digestate will be used to mulch down the two beds.

There we have it.  End of day, or part 5.  The weather has taken a turn over recent days, and I've had to go back to the day job, so progress is now on hold for a short while.  But there's still plenty to do.  I may add another couple of wheelbarrows of digestate to the pile if there is any more left.  The next stint of construction will be the final main timber elements of the build, the timber base rails.

Thanks again for sticking with me and following my build process, and happy growing!