Tips and Instructions for a Poly Tunnel Greenhouse
written by: Sandi Johnson•edited by: Amy Carson•updated: 2/14/2011
Want an easy greenhouse you can build in a day? Follow the instructions below on how to build a poly tunnel green house and you could plant seedlings or starting seeds in just a day.
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Poly Tunnel Greenhouses
The basic premise for learning how to make a poly tunnel green house is simple. Use flexible PVC pipes to create hoops, known as ribs, and then stretch a thin plastic skin over them. Odds are, if you spend any time on gardening or homesteading blogs or how-to sites, you have seen numerous plans. Instructions on how to build a poly tunnel green house often show up as hoop houses, easy DIY greenhouses, or simply poly tunnels. No matter what you call them, these are some of the easiest outdoor structures to build, not to mention inexpensive.
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No matter what height, length or width greenhouse you plan, the methods for building a hoop house or poly tunnel greenhouse are the same. The bigger you want it, the more hoops you make or the wider apart you space their ends. To give a brief outline, rebar rods driven into the ground to hold either end of the PVC hoops. You save the two ends of the tunnel, where the doors are housed, for last, just before you stretch out the plastic skin. Lumber strips on the inside of the hoops help support the hoops and keep them equal distances apart.
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Things You Should Know First
Before you jump right into the instructions for how to build a poly tunnel green house, there are a few things you should know first. Here they are, broken down by greenhouse parts and supply lists. For your supply list, specific numbers and footage depends on the size greenhouse you plan to build.
What You Will Need
4 ft of rebar per hoop (each leg of each hoop needs a 2ft piece of rebar)
Gray PVC pipe (3/4-1 inch in diameter)
2x4s equal to the length of your greenhouse, times 5, plus enough to fit either end at ground level
Drill (if you prefer to pre-drill holes in the PVC)
¾ inch gray UV PVC pipe works best and withstands sun exposure longer than regular white PVC. However, ¾ to 1 inch white PVC works just as well in terms of structural integrity.
Each end of each hoop of PVC has to slip over a piece of rebar, so be sure PVC and rebar fit each other.
Ribs should not be more than three feet apart to maintain structural integrity and keep plastic from tearing, especially in snowy or heavy rain conditions.
Support strips screwed to the inside of the installed hoops at 10, 12, and 2 o’clock positions keep the hoops in place and provide a more sturdy foundation for the plastic skin. Standard 2x4s are the best option.
Each end piece of the poly tunnel is assembled separate from the main structure, and then fitted onto its rebar feet.
Framing the doors in each end piece provides wood to staple the plastic sheeting to, but is not absolutely necessary.
You will need two people to install end pieces.
Any heavy duty clear or translucent plastic will work, however, plastic specifically designed for greenhouses is best in terms of wear.
Plastic should be a continuous piece from one sidewall to the other. Seams should be parallel to hoops.
Keep plastic taut, but not too tight. Too loose, and rainwater or even a light snow can pull down the greenhouse. Too tight, and rainwater or snow will tear through the strained plastic.
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Continue to Page 2 for Building Instructions
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The instructions on how to build a poly tunnel greenhouse are easy enough for a novice to follow. It does not take great carpentry skills or expensive supplies. In Part 2 of Weekend Project, How to make a poly tunnel green house, step-by-step instructions take you from pile of supplies to finished greenhouse in a single weekend. For the gung-ho, the project could be completed in a single day.
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Building the Ribs
In learning how to build a poly tunnel green house, the first step is to build the ribs. The ribs form the structural framework for the rest of the greenhouse. It may take a little experimenting over time to find the perfect build for your particular climate, but these steps provide the basis.
Sink rebar to form two parallel rows, no farther than 3 feet apart. Sink each piece 18 inches, leaving 6 inches above the ground.
Leave first and last rows of rebar for the end pieces. Slip PVC over the exposed rebar. It is best to do all of one side first before moving to the other side.
Screw a 2x4 at ground level on what will be the inside of the PVC hoop. Screw directly into the PVC piping. This provides a base for other pieces, as well as helping to keep the PVC in place. If the 2x4 lifts off the ground, use large zip ties to secure it to the rebar or temporarily use curved tent spikes to keep the 2x4 in place on the ground.
Repeat steps 2 and 3 for the other side of the hoops.
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Building the Tunnel Ends
Methods abound for building and framing tunnel ends and doors. If you read 10 sets of instructions on how to build a poly tunnel green house, and you’re liable to find 10 different methods. The best method is the one that works for your climate, on-hand supplies, and budget. These are the most basic tunnel ends.
Place a 2x4 at the end of your tunnel, touching either side of where the end hoops will slip over the rebar. Mark where the rebar sits on the 2x4.
Screw one side of the PVC pipe to the 2x4 at the first mark. Be sure it can still slip over the rebar once the end is finished. Bend the PVC and screw the other end to the 2x4 at the other mark. You should have an inverted PVC “U" the same size as your other hoops, but secured to a 2x4 on the ends. Trim any 2x4 that extends beyond the hoop.
Wrap plastic snugly around the hoop frame, with the 2x4 away from the plastic. Staple plastic ends to the inside of the PVC piping. If you plan to frame a door in wood, you can alternatively staple the plastic to the inside of the framing. All staples should face inside the greenhouse once the end is installed.
If you are not framing for a door, an easy solution is to cut a door-size opening in the plastic after stretching in around the hoop. Cut a flap of plastic at least four inches wider than the door opening, wrapping and stapling one end at the top of the PVC hoop. Leave enough extra plastic at the bottom of the flap to wrap around a scrap piece of 2x4 to weigh the flap down when you need the door to stay closed.
Slip the ends of the hoop end frame over the rebar and screw into place. (You will need the help of another person to move the complete end frame.)
Install 2x4 support strips on the inside of the greenhouse at 10, 12, and 2 o’clock positions, the length of the greenhouse. Screw the 2x4s to each PVC hoop to keep them at the same distance and provide additional support for the skins.
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Stretching the Skin
Stretching the skin is the hardest part of learning how to build a poly tunnel green house. It takes two people and a lot of experimenting.
Wrap one loose end of greenhouse plastic around a 2x4. Lay the 2x4 on the outside of the hoop at ground level, the same way as the inside 2x4. Screw in place. In short, you want to make a hoop sandwich with the 2x4s as “bread" and the plastic and PVC as filling.
Stretch the plastic up and over the hoops. Be sure to overlap plastic ends by several inches. Staple seems to PVC piping.
On the other side of the hoops, repeat step 1 to secure the loose end of plastic to the tunnel frame at ground level.
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Final Thoughts and Notes
Once you complete your initial build, keep in mind your local weather. The initial design was built on a farm in southeast Georgia (a mild climate) and positioned behind a large existing structure (for minimal exposure to wind.) You may need to make some modifications if you live in an area with regular winter snowfall. Likewise, without a natural wind damper or break, areas with high winds may need additional modifications to prevent wind damage and other issues. Curved rebar or other “U" shaped spikes may be needed to secure ground level 2x4s below ground to prevent a blow-over.
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References and Resources
Poly Tunnel design courtesy of Sandi Johnson
Image courtesy of stock.xchng http://www.sxc.hu/photo/584797