PRACTICAL
The curtains needed to be on a track so
we could open and close the sides. The
curtains were 450mm longer than the
legs and needed to hang vertically, so we
had to find a way to attach the track to
the hoops. We cut holes the size of the
tubes in blocks of wood then cut the
block in two, through the hole, to leave
a semi-circle in each piece. We then
attached a plate to the longer piece of
wood and bolted them back together to
clamp around the pole, as shown above.
The plate was used to attach both the top
cover and the track. We bought the
tracking from a local supplier of body
parts for commercial vehicles.
The corners presented more of a
challenge as they needed to allow fixings
on the side and the ends. These corner
brackets were made from 75mm box
section steel, 150mm long. From halfway
along two adjacent sides were cut away,
and what was removed was welded to
the remaining two sides to create fixing
tabs. Two holes were then drilled in the
corner of the remaining box section to
allow it to be clamped to the tube as
shown. A block of wood and a plate were
bolted to the side to match up with the
other side brackets, and an extension
plate bolted onto the other side for the
end of the tunnel.
Attaching the curtain track to the hoops:
We cut holes the size of the tubes in
blocks of wood then cut the block in two,
through the hole, to leave a semi-circle
in each piece. We then attached a plate
to the longer piece of wood and bolted
them back together around the pole
For the corner
brackets, two
holes were drilled
in the corner of
the remaining box
section to allow it
to be clamped to
the tubeThe top cover
When the frame was erected we
shortened the polytunnel a little and it
was now only 11.4m long. The distance
over the hoop from fixing point to fixing
point was 6.6m. We had decided that the
best way to fix the top cover would be to
roll it around a beam the same length as
the frame, and this would use up 600mm
of cover on each side. We also wanted to
leave a small pelmet of 100mm to cover
the curtain track, so we therefore needed
a cover for the roof of 12m x 8m. After
conducting an internet search we found
a 12m x 8m reinforced clear PE tarpaulin
of 200gm per square metre at a
reasonable price: the supplier also sold
an 8m x 5m sheet which we needed for
the ends of the tunnel.
To fix the sides we used a 75mm x
50mm timber beam made by joining
three 4m lengths together with glued
and screwed scarf joints to create a
beam 11.4m long. These beams were
temporarily fixed to the side brackets with
G-clamps. We draped the cover over the
top of the frame and held it in place with
speed clamps. The cover was then
marked at 425mm from the edge, as
we had calculated that was where the
bottom edge of the beam needed to be
when the cover was fixed. To fix the coverwe first held it in place with staples and
then screwed clamping strips of 75mm x
25mm x 1.5m timber over the top. The
beam was rotated 360° so that the cover
was completely wrapped around it, then
it was screwed to the bracket to fix it in
place. The diagram below shows the
cover as the red and blue lines: the red is
the cover above the beam over the top,
and the blue is the cover below the beam
that leaves the 100mm pelmet.
The process was then repeated on
the other side. To tension the cover over
the top of the polytunnel the clamping
brackets were slackened off and pulled
down on one side and then the other.Filling in
the ends
We needed the
ends of the tunnel
to be removable in
the summer and
in place for the
winter. We used
the 8m x 5m sheet
and cut 3m off
each end: this
gave us two 5m x
3m sheets each
with a cut edge and three edges with
eyelets for fixing. We used the same
method as with the top cover, ie fixing of
the sheet was the same as the sides, with
a clamping strip and a turn around the
beam. Once this was done, three eye
bolts were fixed through the beam to
provide fixings for lines that would hold
the ends of the top cover down. As it was
late spring, and we would not need the
ends filled in, the cover was rolled up
and lashed to the top of the beam.Fitting the curtain sides
We were given the details of a local
commercial vehicle body parts factor,
who sold replacement track for curtain
sides at £5 per metre + VAT. We needed
11m for each side and 5m for each end,
a total of 32m. The track came in 3m and
4m lengths, so we bought four of the 3m
lengths and five 4m lengths. We used
one 3m and two 4m lengths on each
side, and one 3m and half of a 4m length▼ When the frame
was erected we
could start adding
the top cover and
filling in the
ends (below)▲ The red line
represents the
cover above the
beam over the
top, and the blue
line represents
the cover below
the beam that
leaves the
100mm pelmet