Part
I Site Planning and Construction |
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Article |
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Constructing
a Simple PVC High Tunnel
by
Jim
Hail, Robbins
Hail, Katherine Kelly, and Ted Carey |
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Introduction |
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This low-cost, 30’ long
by 18’ wide high tunnel is constructed using PVC pipe
for hoops. The materials cost roughly $500 (including shade
cloth for summer production) and we didn't shop for the best
buy on materials and lumber. A slight disadvantage of the design
is that curvature of the hoops may allow rain to run inside
the edge of the house when the sides are raised for ventilation.
One person can complete most of the construction, but inserting
the hoops and putting on the plastic requires at least two people.
Also, it is nice to have someone to share the heavy work of
driving in the ground posts. A crew of four can easily construct
a high tunnel of this design in a single day. |
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The
dimensions of this high tunnel design may be scaled-down if
you have limited space available for your high tunnel. At a
lesser diameter, or in well-protected locations, it may be possible
to use 1” PVC for the hoops, with 1½” PVC
for the posts. The length of pipe to use for hoops may be calculated
using the formula for the circumference of a circle, (3.14)r,
where r is half the width of your tunnel. Add 3’ to insert
into the ground posts. |
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PVC
will react with the polyethylene greenhouse covering, so in
order to attain the expected 4-year life span of the plastic,
measures should be taken to prevent contact between the PVC
and the polyethylene covering. This may be done by painting
or taping the side of the PVC hoops that will be in contact
with the plastic. Having said that, the oldest high tunnel at
Bear Creek Farm in Osceola, Missouri, is eight years old and
is still covered by its original plastic, which is in contact
with the PVC hoops. |
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Note:
Our procedure calls for driving 3’-long PVC posts into
the ground after laying out the baseboards. We have found this
to be a convenient way to proceed. However, in shallow, tight
or stony soils, it may be necessary to dig holes using an augur,
and then set the posts in concrete. If it is likely that you
will need to do this, then posts should be set before laying
out the baseboards. |
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Materials |
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| Material
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Dimension |
Quantity
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Notes |
| Twine
& Pegs |
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For
corner and baseboard layout. |
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Lumber |
2"
x 6" x 10’ |
6 |
For
baseboards. The boards will be in contact with the soil,
so you might consider a rot resistant wood, such as cedar
or redwood. If you will be growing food crops in the tunnel,
it’s probably best not to use treated lumber because
of possible health concerns.
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1"
x 4" x 10’ |
6 |
For
hip boards. |
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2”
x 4” x 8' |
18 |
Lumber
for attaching baseboards, bracing end hoop, and framing
end-walls. |
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2”
x 4” x 10' |
4 |
Lumber
for framing doors. Depending on door size, amount of bracing
desired amount may vary. We put a 32”-wide door
on each end. |
| Furring
strips |
1"
x 2" x 10’ |
12 |
For
attaching plastic to hip boards and end-walls. Poly tape
may also be used for attaching plastic to end walls. Wiggle
wire is a more costly but convenient method for attaching
plastic to hip boards. |
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40 PVC pipe |
1½”
x 20’ bell-end |
12 |
For
11 hoops + purlin. |
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10’
x 1½”
straight-end |
12 |
For
11 hoops + purlin. |
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3’
pieces of 2” |
22 |
For
ground posts. Requires 8 10' pieces |
| Primer
& Glue |
. |
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For
connecting PVC pipe |
| Carriage
bolts |
4½”
x ¼” |
33 |
For attaching hoops and posts to baseboards, and hoops
to purlin – purchase bolts, washers and nuts. |
| Deck
screws |
1½” |
1
lb |
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2½” |
2
lb |
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3½” |
2
lb |
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| Chain
link fence top rail |
31' |
2 |
For
roll up sides. |
| PVC
fittings |
1” |
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To
make handles for roll up sides. |
| Self-tapping
screws |
. |
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For
connecting top rail pieces, and for attaching PVC handle
to roll-up side. |
| Greenhouse
polyethylene |
30’
x 34’ |
1 |
For
covering the house use 6 mil UV stabilized. For the end
walls, you may use a lighter gauge material, since it
may be taken off each summer to enhance ventilation. |
| Shade
cloth |
30’
x 25’ |
1 |
White
38% shade cloth with grommets sewn every 3’. |
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Tools |
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Step
ladder |
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Level
and plumb line |
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Stapler
and staples |
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Sledge
hammer for driving baseboard stakes and PVC ground posts |
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Saw
for cutting lumber and PVC |
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Drill
with screwdriver bit, and with extended ¼” wooden
drill bit for drilling holes for carriage bolts |
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Site
Preparation and Construction |
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1.
Site Preparation. Choose a good site for locating
the tunnel with respect to light, drainage, access, irrigation,
etc. Prior to beginning construction you may wish to build a
slightly elevated, level pad, or take other measures to ensure
that run-off water will not flood the high tunnel, particularly
in the winter. Orientation with respect to wind is not critical,
but we have oriented ours east west, meaning that prevailing
winds are usually from the sides. |
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2.
High Tunnel Layout. Mark the corners of a rectangular
area 18’ wide by 30’ long. Make corners square
by ensuring an equal distance between perpendicular corners
(should be 35’ between outer corners of pegs). Drive
2”x2” peg into the ground at the corners and stretch
twine around the outsides of the corner posts where baseboards
will run. It is not essential for the tunnel to be level,
but this certainly helps to make doors square. To layout a
level tunnel, use a level to adjust the height of the string
to be used as a guide for baseboard placement. We have built
ours on slight slopes, with the baseboards following the slope,
and hip boards parallel to the baseboards. |
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3.
Set Baseboards. Cut 14 2’ pieces of 2”x4”,
and cut points on ends for driving into the ground. Drive in
these stakes for baseboard attachment on the inside of the guide
string, orienting the broad side of the 2”x4” parallel
to the string. For the long sides of the tunnel, posts should
be 10’ from each end (where the baseboards will meet)
and 6” from the ends (to allow space for PVC ground posts).
Attach the 2”x6”x10’ side baseboards to the
pegs using 3½” screws, starting at one end (snug
with the corner peg). For the end walls, place a peg 10’
from the outer edge of one of the sideboards, and 6” from
each of the corners. Attach the first 2”x6”x10’
(snug against the end of the sidewall baseboard) and cut the
second one to fit. |
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Figure
1. Baseboards laid-out ready for ground post installation. |
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4.
Drive in Ground Posts. Mark inside of side baseboards
at 3’ spacing starting from the end of the sidewall baseboard.
Remove corner pegs and string and drive in PVC ground posts
at corners and at 3’ marks. Posts should go in roughly
to the top of the baseboard, at most. It is possible to damage
the PVC by hitting it too hard with the sledgehammer, or trying
to force it through tight or stony soil. To avoid damaging PVC
with the sledgehammer, have a helper hold a length of 2”x4”
over the end of the pipe, and pound on the 2”x4”.
The helper should wear gloves to protect against jolts.
Note: Our procedure calls for driving 3' PVC posts into the
ground after laying out the baseboards. However, in shallow,
tight or stony soils, it may be necessary to dig hole using
an augur, and then set the posts in concrete. If it is likely
that you will need to do this, then posts should be set before
laying out the baseboards. |
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Figure
2. Ground posts ready to be driven in. |
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Figure
3. Ground posts damaged during pounding. This can be prevented
by pounding on a 2"x4" rather then directly on the
PVC pipe. |
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5.
Hoop Assembly. Assemble 30’
hoops and purlin by gluing together 10’ and 20’
PVC pipes. Use PVC primer and glue, following instructions for
correct use of products. |
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Figure
4. Hoops being placed in ground posts. |
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6.
Raising Hoops. Erect hoops by inserting one end
into a 2” PVC ground post, and bending the hoop to insert
into the ground post opposite on the other side of the tunnel.
Make sure that ends of hoops extend well into the ground posts
(at least 12”). After inserting the posts, make minor
adjustments in the height of the hoops (sight along the top
of the hoops from a ladder) so that all are at the same height.
Drill through baseboard and pipes with ¼” wooden
drill bit. Attach using carriage bolts, washers and nuts, pushing
the bolt through from the outside, and tightening the hoops
snug to the baseboard |
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Figure
5. Drilling through baseboard, ground post and hoop. Carriage
bolts will hold hoop in place. |
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7.
Purlin Attachment. Attach purlin (30' 1½
PVC pipe) to the inside of the hoops. Drill through purlin and
hoops at 3’ spacing, and attach using carriage bolts,
washers and nuts. Head of the bolt should be up to present a
smooth surface to the poly that will cover the tunnel. We put
a piece of duct tape over the top of the carriage bolt before
putting the poly on the hoops. |
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Figure
6. Tunnel with purlin and hip board in place. |
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8.
Hip Board Attachment. Attach hip boards at 3’
height using 1½” screws. Mark hoops 3’ above
baseboard, and attach 1”x4”x10’s end to end,
starting at one end of the tunnel. Ends of hip boards may be
secured together where they meet by screwing a block of wood
across the inside of the junction. |
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Figure
7. Hip board in place. |
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9.
End wall Construction. Use 2”x4”
lumber to frame in end walls. There is no hard and fast rule
for end wall design. However the attached picture shows our
general design consisting of four uprights reinforced by horizontal
and diagonal bracing. Spacing door uprights at a standard distance
(32”, 34” or 36”) accommodates standard door
sizes. Cut notches in the uprights to fit the inside of the
baseboard or the hoop, and attach using 2½” or
3½” screws.
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Figure
8. Tunnel showing end wall design at K-State Research and Extension
Center, Olathe, Kansas. |
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Figure 9. Tunnel showing
end wall design at Full Circle Farm, Kansas City, Kansas. |
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10.
End wall Bracing. Attach end wall bracing. Cut
2”x4” lumber to run from baseboard close to the
second hoop, and attach to end wall and baseboard. |
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11.
Plastic Preparation. Attach furring strips end
to end along the upper half to the hip boards. Alternatively
attach the channel for wiggle wire using self tapping screws.
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12.
Plastic Attachment. It is best to do this on a
calm day. Lay out the poly lengthwise on one side of the high
tunnel. If you are cutting from a longer roll of plastic, be
sure to leave 2’ extra on each end to allow for attaching
to the end walls. Pull plastic over the tunnel. A simple way
to do this is to secure a rope close to the edge of the poly
at each end of the tunnel by placing an object such as a tennis
ball under the plastic and tying the rope around it through
the plastic. Then the rope is thrown over the tunnel and the
plastic pulled over the tunnel using the rope. Make sure the
plastic is well centered on the tunnel and then attach by placing
furring strips over the plastic, snug against and just below
the furring strips already attached to the hip board. Attach
the furring strips with 1½” screws, placed every
2 or 3 feet. Pull the plastic tight and attach to the other
side in the same way. Finish securing the plastic by attaching
to the end walls using additional furring strips. Note, you
may also use poly tack strips (commercially available). |
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Figure
10. Poly attachment to hip board using one furring strip. This
method is less secure than others since poly tends to tear at
the screws. |
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Figure
11. Picture showing the 2-furring strip method of attaching
poly to the hip board. |
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13.
Roll-up Side Installation. Attach
roll-up sides. Assemble top rail pieces to roll up sidewall
plastic with. Make sure the pipe is longer than the tunnel on
both ends so that you can attach a handle to it, and to avoid
difficulties with rolling up sides. Attach the pipe to the poly.
We have used duct tape for this, but a better option is to use
special clips for attaching poly to pipe, which are available
from commercial sources. An alternative is not have roll-up
sides at all, but to simply tie up poly when ventilation is
required. This is easily done by placing eye-hooks in the hip
board at each hoop, and running a piece of string below the
sidewall poly, around the hoop and back. Both ends of the string
are tied to the eye-hook. For roll-up sides, various options
are possible, figure 8 shows a PVC crank that we have used. |
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Figure 12. Poly attachment
to hip board using wiggle wire. |
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14.
Stabilize Sidewalls. Prevent sidewalls from billowing.
To prevent sidewalls from flapping in the breeze, some sort
of support is needed to help keep them in check. Pieces of used
drip tape running from the hip board to the baseboard at each
hoop is effective for us. Using a fender washer along with the
screw prevents screws from tearing though the drip tape in high
winds |
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Figure
13. A drip tape strip from hip board to base board at each hoop
can keep side walls from billowing. |
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15.
Install plastic on the end walls. Since we take
off the end wall plastic during the summer months, we use a
lower thickness end wall plastic. Either commercially available
poly tack strip or furring strips may be used to secure a sheet
of plastic completely over the end wall. Then a hole may be
cut for the doorway. |
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16.
Frame Door. You can make a door, or use an old
door on one or both ends of the tunnel. |
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17.
Shade Cloth Installation. Shade cloth helps keep
temperature down during the summer in high tunnels. In hot years,
we put ours on from Memorial Day to Labor Day. Grommets sewn
into the cloth every three feet allow for tying down to eye
hooks fixed into the baseboards. We skew the shade cloth toward
the south in order to provide better shading on that side. |
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About
the Authors |
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Robbins
and Jim Hail own and operate Bear Creek Farm in Osceola, Missouri.
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Katherine
Kelly owns and operates Full Circle Farm in Kansas City, Kansas.
Katherine Kelly in her newly constructed hoop
house. |
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Ted
Carey, Extension Specialist Food Crops, Kansas State Research
and Extension Center Olathe, Kansas. |
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