Modifying a Caterpillar Tunnel: Part 1
Have a look at this post to learn the beginning steps for transitioning an unheated caterpillar tunnel into a heated, year-round growing space. I elected to take this route and adapt a tunnel incrementally over the course of a season as my profits allowed, rather than take out a loan or wait for a grant and hire a company to build a larger structure. We took on the process step by step and learned a lot along the way. For us, this project made sense and now I have the know-how to repeat it again and again if I like. There are a couple of things we couldn’t do on our own: the foundation, the electrical, and the heating system installation. We hired the experts for those parts. The video post is below and more detail with links follow.
The Foundation:
First, the area was leveled and packed by a local excavation company with a Bobcat. They added “1s and dust” (a crushed stone material) and packed and leveled it to give our tunnel a little bit of a foundation. The gravel is well draining. When the tunnel does take on water due to lots of snow followed by rain, it doesn’t last long. We can also install a french drain in the future if we like. It doesn’t seem necessary right now.
The Tunnel Kit:
We built a Farmers Friend 16ft wide x 100ft long Gothic Pro Tunnel on the packed gravel foundation as instructed by that company - with one exception. I like to pull in the 5ft spacing of the ribs on the kit a little and thereby increase the strength of the structure. I learned to do this because I don’t have 100ft spaces for my tunnels here. They are all 70-90ft long. We get a lot of heavy wet snow here. It only made sense for me to build our tunnels a little stronger with narrower rib spacing. You can now order 50ft or 100ft kits with either 4 or 5ft rib spacing. We order the less expensive 5ft spacing x 100ft kits and just pull them in a little to make them our preferred length.
Baseboards:
We added 1x6” pressure-treated lumber baseboards along the bottom of the tunnel. Clamp the board to your ribs and pre-drill holes for your self-driving screws. It is so hard to drive crews into these steel pipes, even self-driving ones. For me, it just isn’t worth the struggle.
We added wiggle wire channel to the baseboards for securing the plastic. You can find the channel and wiggle wire from Rimol Greenhouses. Here are some direct links to these products to help. Unfortunately, their product search feature was not working the last time I was on the site.
Hip boards:
Next, we add a length of pressure treated 2x4” lumber along the tunnel at about waist height. These “hip boards” will secure the plastic when we cover the tunnel. The hip boards should be low enough that they don’t catch snow and rain rolling down the tunnel’s roof. If they are too high, they will catch and dam up snow or rain. They should be mounted just below the curve of the rib where the pipe is completely vertical.
We use a second piece of 2x4” lumber, split down the middle into 2x2"s to secure our plastic to the hip boards. Alternatively, you could use a wiggle wire channel and wire here. We’ll cover this more when we are talking about the plastic and inflation kit step.
Securing your plastic at this height with hip boards will help prevent the wind from stripping the roof off your tunnel in the event that you have your sidewalls up when a strong wind comes through. The hip boards add additional strength to the tunnels, too. Maybe they aren’t necessary where you are.
Endwalls:
Our end walls are constructed with a pressure treated 2x4” footer that is anchored with rebar (we drill holes through it and pound some rebar into the ground to prevent the walls from slipping moving forward and back.
Next we add pressure treated 2x4” studs using greenhouse stud brackets that we buy from Rimol Greenhouses. There is a direct link below for your convenience.
If you are using Rimol stud brackets with a Farmers Friend Tunnel, you will want the 1 3/8” bracket size.
Doors:
We build very simple doors with 2x4” lumber and hinges from the local hardware store with leftover plastic from the tunnel kit. We make our handles with a clever collection of plumbing parts. See the video to view the handle in action.
The assembly goes like this:
~8-inch long piece of pipe (1” diameter) for the outside handle
elbow pipe (for 1” pipes)
~5-inch long pipe (1” diameter and long enough to fit through the door)
1.25” floor flange for plumbing. (one size larger than the pipe so the handle and fit through it)
Then stick the 5” pipe through the hole in the door
1.25” floor flange for plumbing (one size larger than the pipe so the handle and fit through it) (Same flange part as above)
elbow pipe (for 1” pipes) (same part as above)
~8-inch long pipe (1” diameter) for the inside handle. (Same part as above.)
Add screws for attaching the flanges to your door.
Next up:
In future posts, I’ll explain how we add the plastic and inflation kit, electrical, ventilation, heat, and water in the same sequences that we used to finish our tunnel here.
Please share your questions below. Cheers.
