What This Is
I wrote this post with the hope of helping small-scale farmers build a large, sturdy and economical high tunnel. This design is perfect for winter growing, and can also be used (with a shade cloth replacing the poly skin) for season extension in the summer.
Our high tunnels are 100’ long and 12’ wide, to suit our 100-foot bed length and 3’ bed width with 1.5’ aisles (3 beds per tunnel). The total cost is about $1500, which is a steal for a high tunnel this size (even if it is a few bucks more than the designs it’s based on, for reasons we’ll discuss down the page). Better yet, this is a project that three people could easily manage in a day, even on the first try.
With a little practice you and your two friends could pop up three of these in a good day.
This post relies on two links, in particular: first, Johnny’s excellent 27-page guide to building a high tunnel; and second, Mother Earth News’ diagram of a high tunnel end wall frame.
What To Do
If you want to build our high tunnel, here’s what you do. First, check out the materials list and order what you need (but don’t actually do this first–go ahead and read through everything). Second, proceed as if you were going to build Johnny’s high tunnel, until you get to page 17, where they tie off the plastic in an unsightly and ungainly ponytail and wedge it between two T-posts. Don’t do that.
Instead, follow Johnny’s high tunnel construction plans about 80%. Basically, we build the tunnel according to Johnny’s excellent plans until the very end, when it comes time to tie off the plastic on the end walls. For this step, we use a simple framing approach recommended by Mother Earth News (MEN) and many others.
The advantage of Johnny’s plans is that they are geared toward a simple, strong and highly economical structure. For example, where MEN uses PVC pipe to construct the bows, Johnny’s uses steel fence rail. And instead of requiring hundreds of feet of wiggle wire/track, Johnny’s uses a nifty lacing of parachute cord (total cost: $50) to hold the plastic in place while allowing for easy adjustment up and down.
The disadvantage of Johnny’s plans, as far as we’re concerned, is the absence of a door (or doors). Instead, the ends of the poly skin are simply tied off and staked down. Users crawl in and out under the liftable poly cover on the sides. There’s nothing wrong with this approach. However, there are two disadvantages that led us to build proper end walls with working doors.
First, Johnny’s design assumes two extra aisles inside the high tunnel, one on each side. We prefer to maximize the growing space and run our beds to within inches of the side. In so doing, we actually get a lower cost/square-foot of growing space as compared to Johnny’s design, despite the extra $150 or so it costs to build the end walls. Second, it seems truly inconvenient to slide under the poly skin every time you want to get in or out, especially if you are toting tools/harvest bins/wheel barrows with you. It just seems like a really easy way to put a hole in the (expensive) poly siding.
Enter the MEN’s plans. Many people have built a simple frame for their end walls, but we chose to highlight the MEN diagram for its simplicity. The end wall frame is constructed of treated 2×4’s, with a bottom end board of treated 2×6. You can easily adjust the dimensions to suit the particular widths of your high tunnel and, especially, your door.
Now for our own design touch. We then run dual-track wiggle-wire channel along the top arc of 2×4 frame, and a single-track channel along the doorframe and the 2×6 on the ground. This allows us to attach the large poly skin to the top of the double-track, and then cut pieces of poly to fit on either side of the door.
This greenhouse materials spreadsheet (including links to all the materials) should get you started. (If you decide to lengthen/shorten your high tunnel, check out Johnny’s helpful worksheet, which customizes most of the material list depending on the length you’re trying to build).
Note that some of the materials for this project are from Johnny’s. Their pole-bender is a good investment at $60 even if you’re only planning to build one high tunnel, because it allows you to make near-perfect bends in any standard 1-3/8” top rail fencing. The first time we built a high tunnel, we bent all of the bows by hand using a jig we rigged up from two T-posts and a telephone pole (the result was impressive considering, but the time and stress were nothing near worth it). Johnny’s also sells a nice piece of poly cover (24’ x 125’) that will work very nicely for this 100’x12’ design, including enough extra material on the ends to cover the end walls. If you’re looking to save a little money, these plans replace Johnny’s film with good stuff from littlegreenhouse.com, which shaves about $50 off the total cost. Finally, Johnny’s sells the appropriate cross-connectors that will attach the bows to the ridgeline. These can be hard to find elsewhere in the proper dimensions, and again, they are reasonably priced at $5 for two.
We’ve listed Farm Tec as a good supplier for wiggle wire and the wiggle wire track. This stuff is not cheap at over $1/ft, but good luck finding it cheaper anywhere else. If you do, get in touch!
Just for kicks, I’ve linked to Bolt Depot for all of the (literal) nuts and bolts required for the project. They are a great resource for any kind of fastener, and they have excellent prices. But please note that these (or comparable) materials could be picked up at just about any home improvement store. Ditto for the parachute cord from parachutecord.com—you could find it a lot of places, but $54 is cheap for 1000’ of quality cord.
We’ve included links to Lowe’s for the remaining materials. They could be acquired just as easily at any home improvement store.
What it doesn’t include:
Doors (you can usually find used glass doors at places like the Habitat Re-Store or other used building supply stores). You’ll want to buy your doors before you go about framing the walls, since the dimensions will depend on the door.
Hinges, if the doors you buy don’t have them.
Wood Screws, since you’ll probably have some laying around.
Duct Tape. Duh. Especially useful for wrapping around the joint between the bow pole and the post pole, to prevent tearing on the poly. Similarly, for buffering the end of the ridgepole so that it doesn’t tear at the poly.
Good Drill Bit. ¼” for drilling into metal.
AND…Basic tools, including a drill, a heavy mallet, measuring tape, a hacksaw or reciprocating saw to cut the posts (or have the home improvement store do it, as we did), and a plumb line if you’re super anal.