Monday, April 16, 2012

Economical High Tunnel Design

Compared to off-the-shelf units, this DIY (do it yourself) design can lower cost and increase flexibility.

In early March, Patrice Gros was in Kansas City to offer a workshop while putting up our high tunnel. Niles Home for Children received a Get Growing KC grant for the materials and Lincoln University Cooperative Extension helped cover Patrice's expenses. I was surprised at how easy building our high tunnel was. The most difficult part is to create the tube bender. That requires a template and cutting, bending and welding some steel tubing.

Orientation: Pick a level site to locate your high tunnel. Decide whether you are going to orient it east-west or north-south. I searched for orientation information and it seems that our latitude is on the border between the generally recommended east-west orientation (in northern latitudes) and the generally recommended north-south orientation (in southern latitudes). We positioned ours east-west because it allowed us to easily cover our existing beds and will give all plants the most sun.

Layout: Our high tunnel is 50'x16 1/2'. We marked our rectangle out on the ground with four pieces of rebar. Then we ran a tape measure diagonally from corner to corner. When the two corner-to-corner diagonals are the same length the rectangle is square.

Hoop Spacing: We wanted the spacing to be 6 feet or less. Our hoop spacing came out to be 5' 6". We drove 24" pieces of 1/2" rebar into the ground at the location of each hoop. The hoops will later be slid over and held in place by the rebar.

Hoop Bending: Hoops are made from 1"x1" 24-foot long, 16 gauge, galvanized square tubing. The tubing was bent using a home-made tube bender. The diagram for making the bender can be found on page 2 of the Kerr Center's How to Build a Low Cost Hoop House. Three people are ideal for the job of bending hoops, two persons bending and one stabilizing the curved tubing as it extends up into the air. The bender is moved along the tube making a bend every four inches.

Placing Hoops: The bent hoops are then shoved down over the rebar on opposite sides of the house.

Anchoring Sides to Ground: Along each side of the house at ground level runs a long stretch of 1" EMT conduit. The pieces of conduit are coupled together by metal connectors. The conduit is attached to the bottom of each hoop by a metal strap held in place by a 3/4" #8 self-tapping screw. Five 1-foot soil augers with their "eyes" bent slightly open to accommodate the conduit were screwed into the ground along each side to keep the house from going to Oz in a wind.

Hip Boards: When the sides are anchored to the ground one end hoop is held plumb by tying it to a T-post. The hip boards of 1"x3" lumber are bolted to the hoops with 2"x1/4" carriage bolts at a height of 3 feet along the curve of each hoop. Make sure that each hoop is plumb before drilling holes. Drill holes with the best quality 5/16" bit. The sheet of poly covering the hoop house will be attached to these hip boards using a "U" channel and wiggle wire. After the hip board is in place, attach the "U" channel down the center of the side board from end to end.

End Wall Channel: Screw "U" channel onto the top of the end wall hoops from the ground over the top to the ground on the other side. For this we used #8 3/4" self-tapping screws spaced approximately one foot apart.

Putting On Clear Greenhouse Plastic: It took about eight people to put on the clear Tufflite covering. Fortunately the wind was not a big problem. We adjusted the sheet so that the same amount overlapped at the ground on both sides and over both ends. Starting at one end, keeping it stretched evenly, the wiggle wire was then pressed with the plastic into the channel. It looked great.

Roll Up Sides: Where the Tufflite plastic film draped onto the ground along each side of the hoop house, we now placed a 50' piece of 3/4" EMT conduit, the pieces held together with metal connectors. On a table saw we had also ripped 50 feet of 1 inch PVC into equal halves. The conduit nestles nicely into the PVC halves with the Tufflite in between. Self tapping screws were then drilled through the PVC and Tufflite into the conduit, fastening the Tufflite onto our 50 foot roller. A crank was then fashioned out of the one inch PVC and attached to the roller with a coupler and screws. The whole side could then be rolled up leaving a 3-foot space for ventilation between the ground and the hip boards.

End Walls: These are not finished yet. We are considering two options at the moment. First, we could run 2"x4" lumber across the bottom ends and attach wiggle wire channel to hold down the endwall plastic at ground level. Alternatively, we are thinking about attaching the endwall plastic only to the hoop itself (using the channel we fastened to it), leaving some plastic overlapping at ground level but not attaching it to anything. I'm sure a wonderful solution will arise.

(reposted from Urban Grown, the newsletter of Cultivate Kansas City.  Marty Kraft is a long-time Kansas City gardener, farmer and environmentalist, currently growing food on two main sites associated with Niles' Home for Children. In early March he teamed up with no-till vegetable farmer Patrice Gros to conduct a high tunnel construction workshop here in Kansas City. Patrice has developed a practical, easy-to-replicate tunnel design for use on his Foundation Farm ( near Eureka Springs, AR. Patrice has been a contributor to Urban Grown and we thank him for sharing his expertise with us through articles and workshops. Many thanks also to Marty Kraft for bringing Patrice to Kansas City again and for generously contributing this report. To learn more about Marty's no-till and ecological gardening techniques see his website at

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