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Discussion forum for the various methods and structures used for getting an early start on your growing season, extending it for several weeks or even year 'round.

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Old February 2, 2016   #1
Cole_Robbie
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Default 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.
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Old February 2, 2016   #2
Cole_Robbie
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By the way, here is my previous design, which I mostly copied off another market gardener on the gardenweb forum:


Against a wind storm, the low and flat design is very strong. I think it would take an F1 tornado to blow it away.

But against snow load, it is no match, especially a super-storm that drops 8" of accumulated sleet under the snow:


So that's why the new design has such a steep roof. But now I am going to catch wind exponentially more than with the low design.


I repaired the smashed tunnel and re-used all the old pipe I could. The collapse cost me about $40.
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Old February 2, 2016   #3
BigVanVader
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High tunnel grant? I need that lol! You will need purlins for sure, maybe connect it all with carriage bolts. Outside of that idk what to tell you, that is mighty dang tall and will be under some serious stresses.
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Old February 2, 2016   #4
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I've built my own for years out of whatever was handy, with good success. But the last one I built 3 years ago was a kit that I beefed up by adding joists to each bow. Since last February, it's had 3 different snows on it over a foot deep. The snow last March made a drift on the top that was at least 3 feet deep, narry an issue.
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Old February 2, 2016   #5
Cole_Robbie
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This is a cel phone pic of a high tunnel design in a catalog. This is probably where I am at right now as far as bracing goes:
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Old February 2, 2016   #6
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Quote:
Originally Posted by Cole_Robbie View Post
This is a cel phone pic of a high tunnel design in a catalog. This is probably where I am at right now as far as bracing goes:
Cole that is a bad design load distribution isn't correct for the bracing.
Might work where I live but not any place with a snow load.

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Old February 2, 2016   #7
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I'll take some pics when I get home from work.
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Old February 2, 2016   #8
Cole_Robbie
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Thanks, guys.

My roof is a lot steeper than that design pic, so I am hoping snow will slide off.
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Old February 2, 2016   #9
Hellmanns
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Thanks, guys.

My roof is a lot steeper than that design pic, so I am hoping snow will slide off.
Some times snow will slide off, but most times it won't without heating the inside. I have always designed mine to carry the load. One tends to think that snow will slide off of plastic, that's just not the case.
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Old February 2, 2016   #10
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Here is how I added structural integrity to mine. The addition of the joist and upright, basically makes the bow a king post truss. I originally misstated that I had added joists to each bow..I was at work and thinking on the go..lol. And yes, it should have been cleaned out last fall, but of late work seems to get in the way of everything!
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Old February 2, 2016   #11
pmcgrady
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Quote:
Originally Posted by BigVanVader View Post
High tunnel grant? I need that lol! You will need purlins for sure, maybe connect it all with carriage bolts. Outside of that idk what to tell you, that is mighty dang tall and will be under some serious stresses.
I looked into the grant in my county (Macoupin) it's available, but you have to prove
for the last 3 years your "vegetable farm" has made/sold more than $1000 per year...
Unfortunately, I don't fall into this category... My vegetable farm has lost money for three years LOL, don't make much when you give most of it away. Maybe I should rethink my "produce business"...
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Old February 2, 2016   #12
Ricky Shaw
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Hellmans,

That's a nice design that spreads the down force out, supporting the sides. That seems to leave more open work area as opposed to putting in support posts, and as some do, a top beam.

Last edited by Ricky Shaw; February 2, 2016 at 06:52 PM. Reason: longer explanation
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Old February 2, 2016   #13
Hellmanns
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Hellmans,

That's a nice design that spreads the down force out, supporting the sides. That seems to leave more open work area as opposed to putting in support posts, and as some do, a top beam.
It works well, Ricky! I also use the joists to support the rails I fasten my stakes to. This tunnel is strong enough to support a tomato crop using the stringing method, so I may ditch the stake's altogether in time.
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Old February 2, 2016   #14
Hellmanns
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Originally Posted by Cole_Robbie View Post
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.
Robbie, I bought my 20×96' kit from the Amish here in ky. It came in under 3 grand with me buying the 2×10 base boards and 2×6 hip boards!

In the 2016 catalog, they list a 20×48 for $1,180.26. I'm sure shipping would add to the price. I picked mine up on site.
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Old February 3, 2016   #15
PureHarvest
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Cole, go to rimol.com
You can get a 22x48 which includes frame (including endwall brackets, and two layers of plastic (plus inflation fan) and all hardware for $3,300.

As far as people wanting to know about grants:

There is a USDA NRCS (natural resources conservation service) office in every state. Some states have one in every county
The EQIP program pays for high tunnels. You have to be an ag producer OR show that you have the potential to become an ag producer. Also the FSA (farm service agency of the USDA) has to have your land in their mapping system and assign you a farm and tract number. This step is easy.

So, if you are in a suburb and a hobbyist, you are out of luck.

This year's high tunnel program in my state pays $2.91/sqft if you are a regular farmer. It pays $3.50/sqft if you are a beginning farmer (less than 10 years reporting farm income on taxes) or are a historically under-served individual (minority)/veteran of war.

So a 22 x 48 would pay you $3,072 if you are a regular farmer, or $3,696 if you are new or under-served/vet. And it is flat rate, meaning you get all the money and keep anything above your cost of material. But you must install the size you apply for.

I am an Agricultural planner, so I swim through these details all day long
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