Part
I Site Planning and Construction |
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Article |
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Constructing
a Simple PVC High Tunnel--Metric Units
by
Jim
Hail, Robbins
Hail, Katherine Kelly, and Ted Carey
modified to Metric units by Gary W. Hickman |
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Introduction |
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This 5.5 meters wide by 9.1
meters long high tunnel is constructed using PVC pipe for
hoops. Longer structures, up to 29 m, may be constructed
with the addition of hoops. Additional support and
purlins may be necessary. A crew of four can easily construct
a high tunnel of this design in a single day. |
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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 |
5cm
x 15.2cm x 3m |
6 |
For
baseboards. Use rot resistant wood, such as cedar
or redwood, if available; or, pressure treated lumber
can be used because of possible health concerns
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2.5cm
x 10.2cm x 3m |
6 |
For
hip boards. |
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5cm
x 10.2cm x 2.4cm |
18 |
Lumber
for attaching baseboards, bracing end hoop, and framing
end-walls. |
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5cm
x 10.2cm x 3m |
4 |
Lumber
for framing doors. |
| Furring
strips |
2.5cm
x 5cm x 3m |
12 |
For
attaching plastic to hip boards and end-walls. |
| Schedule
40 PVC pipe |
3.8cm
x 6.1m bell-end |
12 |
For
11 hoops + purlin. |
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3m
x 3.8cm
straight-end |
12 |
For
11 hoops + purlin. |
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3m
x 5cm |
8 |
For
ground posts. Requires 22 0.9m pieces |
| Primer
& Glue |
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For
connecting PVC pipe |
| Batten
Tape |
150m
x 1.9cm |
1 |
For
securing poly to wood frames |
| Carriage
bolts |
11.4cm
x 0.64cm |
33 |
For attaching hoops and posts to baseboards, and hoops
to purlins. |
| Deck
screws |
3.8cm |
0.45
Kg |
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6.4cm |
0.45
Kg |
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8.9cm |
0.90
Kg |
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| Greenhouse
polyethylene |
9.1m
x 10.4m |
1 |
For
covering the house, use (0.15mm) UV stabilized poly. For the end
walls, you may use a lighter gauge material, since it
may be taken off each summer to enhance ventilation. |
| Shade
cloth |
9.1m
x 7.6m |
1 |
Ten
38% shade cloth with grommets sewn every 0.9m.. |
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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. |
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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 should be perpendicular to
prevailing winds if side ventilation is used; and parallel to
winds if end vents are used. The ground should be level,
side to side, and have no more than a 3% slope end to end. |
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2.
High Tunnel Layout. Mark the corners of a
rectangular area 5.5 m wide by 9.1 m long. Make corners
square by ensuring an equal distance between perpendicular
corners (should be 10.7 m between outer corners of pegs).
Drive 5 cm x 5 cm pegs 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 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. If
built on slight slopes, the baseboards should follow the
slope, and hip boards should be parallel to the baseboards. |
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3.
Set Baseboards. Cut 14 0.6 m pieces of 5 cm x
10.2 cm board,
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 5 cm x 10.2 cm board parallel
to the string. For the long sides of the tunnel, posts should
be 3 m from each end (where the baseboards will meet)
and 15.2 cm from the ends (to allow space for PVC ground posts).
Attach the 5 cm x 15.2 cm x 3 m side baseboards to the
pegs using 8.9 cm screws, starting at one end (snug
with the corner peg). For the end walls, place a peg 3 m from the outer edge of one of the sideboards, and
15.2 cm from
each of the corners. Attach the first 5 cm x 15.2 cm x 3 m (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 0.91 m spacing starting from the end of the sidewall baseboard.
Remove corner pegs and string and drive in PVC ground posts
at corners and at 0.91 m 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 5 cm x
10.2 cm board
over the end of the pipe, and pound on the board. As an
alternative to PVC ground posts, metal reinforcing rod (rebar)
can be used. Rebar dimensions are: 1.3 cm x 45.7 cm,
with 30.5 cm in the ground and 15.2 cm above ground.
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Figure
2. Ground posts ready to be driven in. |
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5.
Hoop Assembly. Assemble 9.1 m hoops and purlin by gluing together
3 m and 6.1 m
PVC pipes. Use PVC primer and glue, following instructions for
correct use of products. |
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Figure
3. Hoops being placed in ground posts. |
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6.
Raising Hoops. Erect hoops by inserting one end
into a 5 cm 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 30 cm). 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 0.6 cm 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
4. Drilling through baseboard, ground post and hoop. Carriage
bolts will hold hoop in place. |
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7.
Purlin Attachment. Attach purlin (9.1 cm 3.8 cm PVC pipe) to the inside of the hoops. Drill through purlin and
hoops at 0.91 m 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.
Add a piece of duct tape over the top of the carriage bolt before
putting the poly on the hoops. |
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Figure
5. Tunnel with purlin and hip board in place. |
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8.
Hip Board Attachment. Attach hip boards at 0.91
m height using 3.8 cm screws. Mark hoops 0.91 m above
baseboard, and attach 2.5 cm x 10.2 cm x 3 m 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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9.
End wall Construction. The most critical
components of tunnel greenhouses are the end walls. Use
5 cm x 10.2 cm lumber to frame in end walls. There is no hard and fast rule
for end wall design. However the picture below shows the general design consisting of four uprights reinforced by horizontal
and diagonal bracing. Spacing door uprights at a standard distance
(81.3 cm, 86.4 cm, and 91.4 cm) accommodates standard door
sizes. Cut notches in the uprights to fit the inside of the
baseboard or the hoop, and attach using 6.4 cm or 8.9 cm screws.
If longer lasting end walls are desired, they can be covered
with corrugated fiberglass instead of
polyethylene.
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Figure 6. Tunnel showing
end wall design. |
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10.
End wall Bracing. Attach end wall bracing. Cut 5
cm x 10.2 cm 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.
Note that PVC will react with the polyethylene greenhouse
covering, so in order to attain the expected 4-year lifespan
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. |
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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 0.6 m 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 3.8 cm screws, placed every 0.6 m or
0.91 m. 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. |
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Figure
7. Poly attachment to hip board using one furring strip. |
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13.
Stabilize Sidewalls. Prevent sidewalls from billowing.
To prevent sidewalls from flapping in the breeze, some sort
of support is needed to keep them in check. Pieces of used
drip tape running from the hip board to the baseboard at each
hoop are effective. Using a fender washer along with the
screw prevents screws from tearing though the drip tape in high
winds |
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14.
Install plastic on the end walls. If
planning to 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. For more permanent end walls,
fiberglass may be used. |
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15.
Frame Door. You can make a door, or use an old
door on one or both ends of the tunnel. |
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16.
Shade Cloth Installation. Shade cloth helps keep
temperature down during the summer in high tunnels. Grommets sewn
into the cloth every 0.9 m allow for tying down to eye
hooks fixed into the baseboards. |
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About
the Authors |
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Robbins
and Jim Hail own and operate Bear Creek Farm in Osceola, Missouri.
Katherine Kelly owns and operates Full Circle Farm in Kansas
City, Kansas |
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Ted
Carey, is Extension Specialist Food Crops, Kansas State Research
and Extension Center Olathe, Kansas. |
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Gary
W. Hickman is a Horticultural Consultant for US-AID
projects. For more information, see www.cuestaroble.com. |
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