Here are some answers.

Here is a picture of one of my PVC and wood high tunnels.
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Another one is this. It is much smaller.

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What ever you do, don't use the plastic from Lowe's it is not UV stable and it will degrade, get brittle and break up. It will last for a few months, but that is it. You will replace it all the time. If you are going to build this, then do it right and get some greenhouse plastic, 6 mil. One time and you will be good for 4 years plus! Some say their is an interaction between the PVC and the plastic, but I haven't seen it.

Shade cloth would help with the heat.

Humidity, don't worry about it.

Heat: Don't know about heaters, but if it was free why not? I personally wouldn't use them if I lived in Texas. You can probably garden year around with out much work. I live in Kansas and I have lots of things still growing in my high tunnels with out heat. Just plant the right crops (cold tolerant), use row cover and you will be ok.

Don't try to grow tomatoes in January unless you have experience you probably won't be successful.

Irrigation:

Use drip tape. Why are you wanting to warm the water? Water is water and unless you are trying to grow tropical plants, I wouldn't do that. Anyways the water in the barrel will cool down so you will be watering with cold water anyways.

Hope this helps.

Jay

I would check with the company you are getting the free natural gas from and let them know that you are planning to use that natural gas to heat a greenhouse. You certainly don't want them to see a drastic increase in usage, and come to investigate, see the greenhouse and get upset, causing them to rescind their previous generous offer. Just common courtesy. (You probably already know this, but I figure I would mention it, just in case.) It's really too sweet a deal to potentially lose it for lack of foresight. The cost on their end will rise, and they will probably be very interested in the reason.

Thanks for the replies. Jay you used a term I am unfamiliar with. You said to use "row covers". I am not sure I know what your talking about. So painters plastic is out. Okay, what should I use? What is the material you are using in the bottom picture you posted. Where do I get it? Last year I was looking for steel building insulation for our main eating pavilion. I found a company on the web from North Carolina that had a good price, so bought from them and paid $300 shipping. When the truck arrived, I found that the stuff was manufactured in San Angelo, Texas just 70 miles from me! I could have paid half of what I paid if I would have know that little bit of information.

You said that drip tape is the way to go. So I am guess that you are suggesting bed planting and not pot planting, right? Are talking about direct ground beds? I like this idea much better then pots.

I don't know if it is possible, but my intention for building a green house in the first place is to produce daily use vegetable and herbs year round. Things like onions, bell peppers, carrots, tomatoes, cilantro, mustard greens, collard greens etc. While some thing like carrots are consumable plants that must be replanted, I was hoping to grow other like peppers and tomatoes that don't. Bare in mind that I have zero understanding of the US climates effect such thing. I spent 20 years in the Amazon rain forest and we did not have to worry about greenhouses there, if you know what I mean. You seem very knowledgeable and I value your advice.

eaglesgarden, I appreciate your concern for the oil company. I assure you that everything we do with their gas is presented to and approved by them before we proceed. As the director of a life rehabilitation center I understand that relationships can only grow in the soil of trust and mutual respect. Relationships I know how to grow. It's plants I have a problem with. LOL! :)

Here is another of our high tunnels that covered in greenhouse plastic.

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The plastic is 6 mil greenhouse plastic it has uv inhibitors and has a 4 plus year life span.

Just google greenhouse plastic, there are lots of types/brands. I use Klerk's K-50.

Row Cover is a spun-bond Polyester fabric to protect plants from insects and frost. Common brands are Gro-Guard, Agri-Bond

Here is a picture of row cover in use to keep grasshoppers out of my spinach and lettuce this fall.
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Yes drip tape on 30-36 inch wide beds. Depending on the crop I have 1-3 rows per bed.

Just because you have a greenhouse doesn't mean you can grow anything you want year around. While you have free heat, is it really worth it to use all that energy to grow a crop when you could just as easy grow a crop without that added heat?

I think you should contact your local extension service and have them help you for your specific area. Also, check out or buy the books from Eliot Coleman.

http://www.fourseasonfarm.com/

I think reading these books would really help you out to understand what is possible and what a steep, but doable, learning curve you will have.

As far as me, I am a teacher and market gardener. I have been doing this for 6 year now. We are just starting to grow our "micro farm".

Here is a link that might be useful: Our farm Blog

I second the Four Season Farm site and Coleman's books for the beginner. Learn them. Live them. Love them. It is essential to understand plant needs and what happens with hoop house material. Once the basics are understood, it is fairly easy to extend the season and grow year-round (except maybe in TX in summer, but the point is growing in winter under hoops). Coleman is very good at explaining and showing the basics.

Dan

Thanks. I will order the books right now. I ordered several highly recommended (amazon.com reviews) books about gardening in Texas earlier this year, but they turned out to be mostly about landscape gardening (flowers and shrubs), not vegetable gardening. They were also written by people of the Martha Stewart mentality that placed more importance on aesthetic quality then functionality and practicality. I was very discouraged that I had wasted about $100 on books that were not what I needed. I have been afraid to risk buying books on the web again. Thanks for the advice.

In my view, out there your glazing material/film needs to be extra thick to withstand the wind and the dust it carries. You can compensate for occasional hail, but wind will shred cheap film faster than you can say 'double T victory'. Here on the Front Range out in the open it is common to see 11mil.

Dan

Thank you Dan. You have expressed my concern to a T. My land sits on a bluff overlooking what I like to call the Big Country Valley to the south of us. I can see over 30 miles to the south of me which is where all my strongest winds come from. In 2009 we had three days where wind gust reached 80 MPH. Now 2009 was a very windy year and 2010 has been the least windy year we have seen in decades. But it is not uncommon for us to see 50+ MPH wind speeds a few times a year. The place I plan to build the greenhouse has a line of mesquite trees on the south side of it which should give it some protection from our strongest winds. But I have a feeling that no matter how thick the plastic, it will not survive some of our wind storms. That is why I asked about covering it with shade cloth in my original post (nobody has commented on that as of yet). As I said before, the heavy duty shade cloth that we used for our chicken shade covering is the only flexible material that has survived our here. I don't know what it is made out of but it is over 4 years old and is still super strong. If I could find a similar material that is not as tightly woven and would let more light through, I could cover my greenhouse with it and it would hopefully protect the poly and provide some protection from the intense summer heat. If light becomes an issue, I could always compensate with some grow lights. Most people only have heat and cold to deal with. I have wind to deal with as well. If not dealt with in advance, one of our wind storms could destroy everything in a single day. That is why I am here for ideas. As a free will supported ministry, I take the issue of stewardship of the resources given to me very seriously. I don't believe in gambling with God's money. Thanks for the advice.

Look for shade cloth on some of the greenhouse sites. They will offer shade cloth in different weights.

We have lots of wind up here too - you must constantly watch the wind on the plains. In my view one of the best sites as far as selection and ~price is Growers Supply.

Dan

At our farm, we sit on top of a hill and we can see for 25 miles to the west and 15 miles to the south. We have 5 trees on our property.

We have had winds in the 70-80 mph range and haven't had any problems with 6 mil plastic. We usually get 30-40 mph winds on a weekly basis.

I don't see wind as an issue as long as you build your structure sound.

Jay

Thanks. I traveled up to Lubbock this week (about (150 miles north) and saw a bunch of greenhouses just north of Post, TX, sitting on the edge of the Caprock (a sort of long ridge that divides the lower plains of west Texas from the High plains or "Llano Estacado"). I stopped in and talked to the owner. He gave me a tour and was extremely helpful, the most friendly guy you would ever want to meet. He has 8 hoop style houses that I would guess to be about 80 feet long by 20 feet wide. He uses two layers of plastic and some kind of blower to force air between them. He uses an aluminum C-channel track with what he called "Wiggle Wire" to hold his plastic on. Unlike other greenhouses I have been seeing on the web, his houses have solid plywood ends and solid half walls four feet tall. He does use black shade cloth and said it really helps to reduce summer heat. I ask about reducing the light to much and he just laughed and said, "Son, we don't have light problems here in Texas." He grows year round and uses vented gas heaters in the winter. But he is not growing vegetable, he grows flowers. I don't know if that make a difference or not. One more thing he said was that he does not use 4 year plastic, just one year plastic. He did not really explain why, that's just what he said. Is one year plastic a lot cheaper then 4 year?

C-channel and wiggle wire can certainly get your film taught enough to withstand most wind (if stretched in sun), at significant additional expense over simple purlins; you are paying for fewer headaches down the road with such a setup (the sound structure Mr Slick mentions above. The 1-year is indeed cheaper than 4-year (again, check out Grower's Supply for an idea).

With good film you also get light dispersal and you can also get good drip control/anti-condensate and IR control as well. Flowers are a different animal than veggies, and warm-season crops ~need min temps in the 50s - hi 40sF to set and ripen.

Geeky tangent: you have your 'palisaded plains' and I can see the Rampart Range from my house. Interesting how people give new place names when they don't name them after themselves or a deer.

Dan

I started this thread a long time ago and have already build my GH, but thanks for the advice though. I built mine out of 2" black poly pipe, which I got for free (Oil Field junk).

Here is a pic. I don't have it covered yet though.

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jungleexplorer-
Great-looking GH. How big is the footprint? I'm guessing 15 X 30?

Thanks. It is 20' X 40'.

Impressive. What are your plans for what you'll use it for?

I am hoping to grow vegetables in it year round. I am going the use double 6 mil plastic with an inflation blower to provide some insulation. I have installed two 8' X 30" evaporative cooling wall panels on one end and two 1300 CFM exhaust fans on the other for cooling in the summer and plan to have heat to keep it above 40 degrees in the winter. My biggest problem now is getting enough people out here on a non windy day to put the plastic on. It has been ready for plastic for over two months and I can't seem to get enough people together at once to do it. I even had a hamburger cook out to try to get it done (only one person showed up).

Too bad I'm 1500 miles away, or I'd volunteer to help with the plastic! Good luck. Hope you get it on in time for the winter. It sounds like it is going to be a wonderful greenhouse.

Thanks. Distance is the problem for everyone. I live in the middle of nowhere. It's a 60 mile round trip for anyone to get here. But I am not too worried. I just need to scrape enough money together to pay everyone's gas and have a BBQ. That should get them to come. LOL!

Did you give up on painting the hoops white like I mentioned on another thread? Maybe it won't get too hot and cook the plastic. Let us know if it does; I just want to know for my own sake. I go through a lot of effort to make everything white; maybe that's a waste of time.

And I'm only saying this in an effort to be constructive and helpful, but I am skeptical that your cooling and ventilation setup will be adequate. The evap cooler won't lower the temp as much as the sun raises it inside the house. And if you turn on the vent fan, you're exhausting the air that you just cooled with the cooler, making it use more electricity and be less efficient. If you run the fans by themselves, the vacuum will suck in the first available air, which will be around the doors underneath the fan, and the other end of the house will be much hotter.

It's not too late to add roll-up sides. I'd also put one of the vent fans at the other end. And like I said in the other thread, I'd paint everything white and also plan for all of the treated lumber to ooze out a corrosive arsenate goo like mine did to me. Maybe the swamp cooler would help you to get nighttime temps down, for the sake of something like tomatoes, which need a cool night to set fruit. But I don't think the cooler will be any match for the sun.

You are obviously good at building things. If you want an engineering challenge, build an automated system to move your roll-up sides up and down, based upon temperature and weather. The key is using the free energy of the wind to vent your air instead of having to pay for it.

Good luck with everything. Sorry to be so critical, but I want it to go well for you.

Hi Cole. After talking with several people, that have used the black poly pipes for hoops, they said they did not have problems with them getting too hot.

As far as your observation on my evaporative cooling system goes, I think you are not familiar with how an evaporative cooling system works. It is strictly a pass through system. It is not like a recirculatory refrigerated cooling system where you are trying to seal a place up as tight as possible, and the same inside air is recirculated through the cooler over and over again. You must have constant air flowing in and out of a house for an evaporative cooling system to work. Here in the south everyone used to use evaporative coolers to stay cool in the summer. I used one for years myself. The way my cooling system is designed to work is basic science. The exhaust fans will exhaust the hot air which is rising to the top of the GH and this will cause a vacuum which will pull air in from any available hole. I have sealed every hole possible other then the evaporative panels, so the large majority of air will entering through them. The air that will enter through the evaporative panels will be a lot cooler then the air inside the GH and will naturally fall (hot air rises, cold air falls). This cooler air will settle along the ground of the GH keeping the plants cooler. As this air heats up it will rise to the top and be replaced by the cooler air coming in through the panels. You see, the exhaust fans will never be exhausting cool air, this defies the laws of physics. The object here is not to create a uniform temperature inside the GH from top to bottom, but only to keep the lower few feet cooler. When I say cooler, I do not mean 50 degrees here, I mean less then 100 degrees (hopefully around 90 degrees). In the end, I will end up with a temperature difference inside the GH. The upper air will be hotter then the lower air. There is no question here that there will be a temperature difference. The question is, how much of a difference it will be. Will it be 5 degrees or 30 degrees. There are too many variables involved to calculate this now, so I will just have to wait and see how it goes and report back here with the readings when I get them. Unfortunately, this will have to wait until next summer. If in the end, my system proves to be ineffective at keeping the lower part of the GH cooler, I will go back to the drawing board.

You see, the exhaust fans will never be exhausting cool air, this defies the laws of physics

Actually, they will. If they're on, they have to exhaust something. As soon as they run out of hot air, cooler air gets pulled up to replace it, or more correctly, pushed by the outside pressure as displaced air replaces itself.

I didn't realize the cooler was also a passive intake vent. If you move enough air out of one end and it gets replaced mostly from the other, then yes that will work a lot better. That's the same concept as roll-up sides. It just takes a lot of energy to use fans, and you said you don't have a lot of money.

Just fwiw, I'm way north of you in zone 6, and in the February sun, my 14x48 greenhouse will get over fifty degrees warmer than the outside temperature. With each 4x7 end door open, it's still about twenty degrees hotter than outside. Depending upon the wind, I have to roll up the sides when the temperature is about 85 or more. The greenhouse then becomes worthless as soon as summer hits and it's 95 degrees outside - it's miserable to be inside, and that is even with the sides up, doors open, and having painted the plastic for the winter with a diluted latex paint. Shade cloth is all that would make it bearable.

If you want to use that building in the Texas summer sun, you should plan on swapping the poly with shade cloth in the summer. That's what would make it be valuable for longer than a short season - the protection it provides from the scalding sun.

Like I said, I want to see it work well for you and your organization. If you're trying to make a profit or at least pay the bills, you might look for any commercial greenhouse operation near you and see what they do.

The exhaust fans are thermostatically controlled. One will come at 90 degrees and the other at 100. So the will not be 24/7 but only when needed. Hopefully it will not cost that much. I am not sure at this point if their draw will be enough to create an actual wind flow powerful enough to overcome the stack effect, but we shall see.