New High Tunnel

Cole_Robbie · February 2, 2016

My mom and step-dad wanted a high tunnel after they saw me build one for myself. But they were adamant about wanting a steep enough roof so the snow slides off, and also for it to be tall enough to not hit their head on the sides.

We got the first few purlins up yesterday:

It's not a kit. The posts are 8' chain link posts sunk 2' into the ground. The purlins are chain link top rail. The peak is a 1.5" emt 90 degree conduit elbow. The 45 degree angles coming out of the posts are 1 3/4" 90 degree emt elbows cut in half. I'm using a pvc 2" connector piece inside the top of the post as a spacer. There's also a little piece of 1.5" emt conduit that I use as a spacer coming out the top of the post, to get everything to fit together snugly. Tek screws and carriage bolts at the post hold it together.

Dimensions are 20x48'. The peak is about 17' in the air. From the peak, down each side to the post is 13' of top rail.

Why not just buy a kit? Money. A kit this size is $5,000 and that does not include lumber or plastic. I can build the metal frame for 1/3 that price. We're going to come in under $2,500 after lumber, plastic, and end walls.

We applied for a high tunnel grant last year and didn't get it. They just called last week and said we were approved for 2016. But it can't be this structure, because we already bought the materials and started on it. That's fine. We'll just build another. For a structure this size, the grant money is about $10k. They said if we could build it for less than that, then we are welcome to keep the difference and call it labor costs.

There will be one purlin bar going down the peak, and 2x4s along the top of the posts. I am undecided about running another purlin bar down the middle of each roof side. I don't want water to pool and collect on the plastic. At a minimum, I will make a diagonal bracing bar for each side of the end purlin. The end takes the most wind force. High tunnels collapse when the end purlin twists past a certain point. I'm going to leave the top of the ends uncovered, so the wind can't push against them. That will also vent heat.

Another option would be to make interior cross bars that connect each side of the rafter purlins, like the horizontal line in a capital letter A.

I obviously have no training or education in architecture, engineering, or even basic math. When I drew it up, I had 15' roof sides, we had to cut them to 13' to make them fit. So that 10th grade sides of a triangle geometry was a little over my head. If anyone has suggestions for making the structure stronger and more wind-resistant, I will certainly listen.

February 2, 2016	#1
Cole_Robbie Tomatovillian™ Join Date: Jun 2012 Location: Illinois, zone 6 Posts: 8,407	New High Tunnel My mom and step-dad wanted a high tunnel after they saw me build one for myself. But they were adamant about wanting a steep enough roof so the snow slides off, and also for it to be tall enough to not hit their head on the sides. We got the first few purlins up yesterday: It's not a kit. The posts are 8' chain link posts sunk 2' into the ground. The purlins are chain link top rail. The peak is a 1.5" emt 90 degree conduit elbow. The 45 degree angles coming out of the posts are 1 3/4" 90 degree emt elbows cut in half. I'm using a pvc 2" connector piece inside the top of the post as a spacer. There's also a little piece of 1.5" emt conduit that I use as a spacer coming out the top of the post, to get everything to fit together snugly. Tek screws and carriage bolts at the post hold it together. Dimensions are 20x48'. The peak is about 17' in the air. From the peak, down each side to the post is 13' of top rail. Why not just buy a kit? Money. A kit this size is $5,000 and that does not include lumber or plastic. I can build the metal frame for 1/3 that price. We're going to come in under $2,500 after lumber, plastic, and end walls. We applied for a high tunnel grant last year and didn't get it. They just called last week and said we were approved for 2016. But it can't be this structure, because we already bought the materials and started on it. That's fine. We'll just build another. For a structure this size, the grant money is about $10k. They said if we could build it for less than that, then we are welcome to keep the difference and call it labor costs. There will be one purlin bar going down the peak, and 2x4s along the top of the posts. I am undecided about running another purlin bar down the middle of each roof side. I don't want water to pool and collect on the plastic. At a minimum, I will make a diagonal bracing bar for each side of the end purlin. The end takes the most wind force. High tunnels collapse when the end purlin twists past a certain point. I'm going to leave the top of the ends uncovered, so the wind can't push against them. That will also vent heat. Another option would be to make interior cross bars that connect each side of the rafter purlins, like the horizontal line in a capital letter A. I obviously have no training or education in architecture, engineering, or even basic math. When I drew it up, I had 15' roof sides, we had to cut them to 13' to make them fit. So that 10th grade sides of a triangle geometry was a little over my head. If anyone has suggestions for making the structure stronger and more wind-resistant, I will certainly listen.