Hoop house height question

zest88April 22, 2014

Hello all.
I was wondering if you could help me out on a hoop house question. I'm going to be building a HH this summer, preferably 20 ft wide by 50ft long. I would like the height inside to be at least 15 feet high. How do I go about calculating this? I grow some pretty big plants and want to make sure I have enough space in case I need it or if I want to hang fans to push the air out of the top. M thinking of adding in sidewalls and roll up curtains to allow airflow. I'm not sure how tall they should be and how much pvc I will need to obtain my goal of 15ft high. I plan on using schedule 80 electrical conduit

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That is very high for conduit. Wind will be your worst enemy with a structure that high so you'll need to reinforce well. My recommendation would be to settle on 10-11 ft with what materials you are working with. I didn't even go that high with 2 3/8" dia. steel pipe.The rollup sides are an excellent choice.

As a rule, you can figure on half of a circle laying on its side so splitting 15 ft (height) and 20ft (width) or about 17.5 ft is the guestimate radius. Diameter of the imaginary circle is 35 ft. Since the perimeter of a circle= pi * diameter (3.14 * 35), your arches (half perimeter) would be close to 55 ft.
If you want more accuracy you'll need to trace it out to scale and measure.

    Bookmark   April 22, 2014 at 10:55PM
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fruitnut Z7 4500ft SW TX

Unless you are snow free and wind never exceeds 30 mph your design is way too weak. Even at 10-11ft it's too weak. For 15ft tall you need a strong steel frame. Mine is 16ft tall and built to 70 mph wind load. When the wind gets up it shakes not violently but it vibrates. This with 2.5 to 3.5 inch steel frame that's strongly braced.

Here's the other thing about a high tunnel. The top half depending on your climate may be too hot for your crops. That part of a high tunnel is basically just a place to exhaust hot air. The bottom half is for cool air intake and growing your crop.

Also I'm skeptical of using fans to help exhaust the hot air. It might help but then again it might just disturb the natural draft. If your crops are heat sensitive you'd be better off with a wet wall opposite large exhaust fans in a full out greenhouse.

This post was edited by fruitnut on Wed, Apr 23, 14 at 12:12

    Bookmark   April 23, 2014 at 12:02PM
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I made my 18.5' wide tunnel 8' high at the center. Above 8', wind load becomes a concern. I think it increases exponentially with each foot higher that you build. Steep roofs catch wind, low and wide roofs are great for shedding wind, but are the worst about holding snow and collapsing.

20' wide and 15' tall is more of a gothic arch design than a hoophouse. You can also make an a-frame with straight walls and a 45 degree roof to get similar dimensions.

    Bookmark   April 23, 2014 at 8:38PM
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jrslick (North Central Kansas, Zone 5B)

I have a friend that used 1.5 inch PVC and had 30 foot bows. He added 3 interior braces, one down the middle and one on each side. While it is still in use, it moves a whole lot! He also had a bad storm and the wind sheared off 7 or 8 bows near the ground! He was able to add some couplers and drove some longer metal pipe in the ground and was able to salvage it.

55 foot hoop would be a disaster, imo. I have two steel framed high tunnels and the are 12 feet 9 inches tall and I know they flex, can't imagine a 3 foot taller one make with PVC. I also have 2 PVC ones. They are 18 wide, 45 long and 8.5 tall.

Another idea, it you really want that tall, what about going down? You could build a 10 foot tall structure and dig out the middle 5 feet and then you would have your 15 feet.


    Bookmark   April 24, 2014 at 2:46PM
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sand_mueller(z 7a, oklahoma)

Hoop houses are cheap to build and unless they are big and tall they overheat rapidly and ventilate poorly. From a growers standpoint they are a lousy greenhouse design, plus they are usually glazed with pvc...one of the worst and trashiest of all human polluting materials. Check out building a greenhouse with 2 x 4 construction, nice and tall with lots of ventilation top, bottom and sides so you don't have to run a big fan. Check out used window glass and you'll be amazed at how cheaply you can build a good greenhouse.

    Bookmark   April 29, 2014 at 3:19PM
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fruitnut Z7 4500ft SW TX

Window glass in a greenhouse would have a useful life of 1-2 yrs here due to hail. Is it really that much better in OK? Plus I won't feel safe under window glass anytime the wind got up. Is this tempered window glass you are talking about? Is that safe? Still don't see it lasting in the hail.

    Bookmark   April 29, 2014 at 10:18PM
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sand_mueller(z 7a, oklahoma)

Hello Fruitnut. Haven't had any serious hail here since I put the house up. The house isn't a large one: 8' x 26', so the glass on the roof is steeply angled. It would take some serious hailstones to break the glass that's in aluminum frames, but some of the steepest part are old single pane glass, but in four sections so each piece is only about 6" x 24". the house has already stood up to 50 mph winds and a snowstorm that collapsed my friends tubular steel greenhouse. If a big storm is happening I an not to be found in the greenhouse. By the way I am a big fan of citrus in the greenhouse and have sprouted a bunch of poncirus tri-foliate seed (hardy orange) for rootstock down the road.

    Bookmark   April 30, 2014 at 6:03PM
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