Mid-Tunnel Setup

A Pictorial Guide to Preparing and Installing Gothic-framed, Outdoor Winter-ready Mid-Tunnels

: Not quite low, not quite high … let’s call it mid.

: Conduit benders can be purchased from most hardware stores. A bender manufactered by benfield is shown here.

: The head of the conduit bender is cleraly marked with angle lines that guide the bending of pipe to specific angles.

: Frame picutred in this gallery are made from 0.5 inch x 10 ft EMT conduit, available from a local retail outlet at a price of $1.74/piece.

: These frames can be made by one person but having a helper is best. Also, when using this method, the working surface must be smooth and firm. Layout a 10-ft section of pipe and tape measure side-by-side.

: Make sure the end of the rape measure and pipe stay in place.

: Pre-mark bend locations. In these frames, bends are centered 2 ft from both ends and at the center of the 10-ft section (2, 5 and 8 ft from the “0” end of the ppe). The first mark is shown here.

: Pre-mark bend locations. Here, the second mark is being made at the center of the 10-ft section.

: Pre-mark bend locations. Here. the third mark is being made 8 ft from the “0” end.

: The pipe has been marked where bends will be made. Now, the pipe is put in place in the bender. The mark in the center of the pipe (5 ft from both ends) locates the middle (high point) of the bow. This 90° bend is made first.

: Align the correct positions on the bender and pipe. On this conduit bender, the 5 ft (90° peak bend) mark is aligned with the arrow.

: Begin the bend with a step and pull on the blender. Be careful! Use proper push and pull form and pace to avoid injury.

: Continue the bend by the step-pull method. Use proper push and pull form and pace throughout the process to avoid injury.

: Pushing down tends to be the most efficient way to start the bend. Heavy footwear (boots) may be best if bending many frames.

: Continue the bend by the step-pull method. Use proper push and pull form and pace throughout the process to avoid injury.

: Complete the bend by stopping at the correct angle (in this case, 90°). The bar of the bender should be only slightly above the line that bisects the peak of the frame. Conduit may ‘spring’ back slightly after being bent. Therefore it may be necessary to slightly over-bend to maintain a 90° bend.Being the bend with a step and pull on the blender. Be careful! Use proper push and pull form and pace to avoid injury.

: Slide the bender along a straight section of pipe to either mark 2 ft from the end (e.g., to the mark on the section on the ground).

: The first and third marks (each 2 ft from opposite ends of the pipe) made at the beginning of the process are visible at the top-center and right-center of the image. Each locate where a 45° bend will be made to form the sidewall.

: As before, align the corret positions on the bender and pipe. However, the remaining bends are each 45° and aligned with the star on this bender.

: Repeat the step-pull method to complete the second bend. This bend will create one straight sidewall of the frame. At this stage, having a partner helps ensure that bends remain aligned.

: For each of the side bends, the 45° angle mark will run paralletl with the pipe when the pipe is completely bent.

: Remove the pipe from the bender. Place the bender in the correct, pre=marked position on the opposidte end of the pipe. Again, with this conduit bender, the 2 ft bend mark is aligned with the star.

: Repeat the step-pull method to complete the final bend. This 45° bend will create the second straight sidewall of the frame.

: Complete the bend by stopping at the correct angle. The bar of the bender should be only slightly above the line that bisects the turn from the frame’s sidewall to its roof.

: A complete frame measuring 45 inches high at its peak and 4 feet wide post-to-post.

: Bend 1: peak (90°)

: Bend 3: sidewall to peak left: (45°);

: bend 3: sidewall to peak right (45°)

: We place frames over 2-3.5-foot sections of used reard. Rebar is sturdy and can be re-used and driven into many substrates. Longer sections have provided sturdier support.

: Rebar is driven with a light sledge. Again, be careful and recruit help, if possible.

: Rebar driven into the ground until approx. 1 foot remains exposed has been sufficient to support frames.

: The tunnel frame is simply slipped over the rebar.

: One frame and two sections of rebar that, ideally, are aligned.

: Frames can be installed and removed by one person but a team is better.

: Frames are relatively easy on-easy off and portable.

: The gothic-framed bows are wide enough to cover a standard raised bed common in vegetable production. Here, though, the bows will cover an unconventional grwoing system comprised of containers held on standard-size pallets.

: Bow are in place and covering has begun. Here, 12 ft wide x 80 ft long sections of 6 mil greenhouse film are secured with cement blocks. Additional steps are required to secure the plastic where high wind and heavy snow is expected.

: Many hands make light work. However, covering low tunnels tends to be easier and more flexibly scheduled than covering a high tunnel.

: Outdoor raised beds were initially covered with light, vented film over u-shaped bows in early fall. Here, the u-shaped bows are being replaced with gothic-framed bows which will be covered by heavier film and remain in place over-winter.

: Of course, u-shaped bows topped by light, vented film can remain in place over winter, covered by taller and wider gothic-framed bows topped by heavier film.

: Bow spacing must be narrow enough and plastic must be of the proper strength and be properly secured to withstand wind and snow loads. These hoops are placed every 5 feet. Snow in 2011-2012 has been lighter than normal. However, since Nov-11, these mid-tunnels have withstood winds of up to 38 mph and snowfalls of up to 4 inches.

: These frames cover wood-sided raised beds. Plastic shown here is secured with only sandbags. Simple, inexpensive steps can be taken to tighten the plastic, which is recommended. For example, it is possible to secure the plastic with wiggle wire on one or both sides of these wood-framed beds.

: These frames have a width:wall height:peak height ratio of 2:1:1.9. In that respect, they do not create miniature gothic-framed high tunnels.

: The width:wall height:peak height:length ratio of this high tunnel = 5:1:2.3:13.3.

: The width:wall height:peak height:length ratio of this high tunnel = 5:1:2.3:13.3.