Johnny's Seeds sells a pipe bender that allows you to make a 12' wide by 7' high tunnel, at whatever length you choose, out of chainlink fencing rails. I bought the bender and built the hoophouse. It's sturdy and effective. There are limitations to building a high tunnel so narrow, but it's a cost effective model, especially for those without long-term tenure on their land. And if you hate frigging around with low tunnels like I do, these walk-in tunnels are a great option for not much more investment.
Here's the thing though: I've since found similar DIY designs online, like this one, that use PVC pipe instead of the aluminum fencing toprail. You sacrifice a lot of sturdiness with these models, but you gain the following:
- Ideal for quick setup and takedown. There are a few reasons why you might like to make these high tunnels fairly portable, just like low tunnels. My tunnels are 12'x75', and I can easily put one up in a day from start to finish. I like to move mine around the farm as a form of rotation. The Johnny's model requires sinking some somewhat permanent ground posts, and all the nuts and bolts involved make setup and takedown a lot more cumbersome.
- Cheaper up front, sort of. Two ten foot pieces of top rail to make one twenty foot long hoop will run you between 12 and 24 bucks; one twenty foot piece of 1" PVC makes the same hoop for between two and five bucks. Then again, you'll want to space the hoops every three feet instead of the five feet spacing you can use with the toprail hoops. You'll still come out ahead, though the PVC hoops will become brittle over time. You can lengthen their life by painting them with UV resistant paint before you use them, as I did.
- Less stress during the initial build. Bending the toprail pipes for the Johnny's model is time consuming and awkward. Drilling all the holes needed, ditto. I love the one Johnny's high tunnel I built. But I hated building it. If, like me, you'd take a kitchenaid over a dewalt, the PVC model is way simpler.
My adaptation of this model is flimsy and ugly as all getout, but it give me some decent season extension for a very small investment, and is easy to move around. I've got a bunch of photos of the latest round of setup (I take them down in the winter. The Johnny's model handles snow with no problem; the PVC model will collapse unless you space hoops close together (2 ft maybe? Haven't tried) or add support to some of the hoops with 2x4s through the winter. I've added captions to some of the photos to provide comments about the design and setup.