L20 x W16 x H9 Greenhouse Structure. Please Help.

azee_2009April 5, 2012

Hello Everyone,

I have to construct L20 x W16 x H9 rooftop greenhouse. I have to take two things to consider at first.

1st is, it should survive outside temperature in summer that will be 45-48 at its peak. (keeping normal temp inside would not ba problem for me).

2nd is, it has to tolerate heavy wind blows & rains etc so it can standwith without any damage.

Anyhow, 1st i had decided to the structure by wood but it goes very coslty.

I am thinking for using

1-1/2 inch angle iron to use as main pillers for (vertical usage) &

1-1/4 inch angle iron to use vertically all the way around.

What do you guys suggest?

One more thing:

I am not using Polycarbonate Sheets for being expensive too.

I will use thick polythene rolls that will be in direct contact with angle frame.

The apprehension is that polythene sheet over angle iron frame may get damage or get melt due to heat of summer or hot angle itself.

What do you guys recommend what should i do? What should be the minimum thickness of polythene sheet i should use?

How should this polythese sheet should be affixed with angles.

Looking for help.

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1.1/2" angle for vertical members isn't really a good idea. hopefully when that big typhoon hits it'll just rip off the plastic and not deform the angles too much.

    Bookmark   April 5, 2012 at 3:12PM
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Hello azee_2009,
First thing is cooling your greenhouse in 118F temps is going to be challenging, especially on a rooftop. I'm building a similar greenhouse in our backyard (10 feet wide, 20 long, 9 tall on the sides and 11.5 at the apex). I also live in the desert where are summertime temps reach over 120F. I'm going to be using a mutli steep cooling plan. The hart of the cooling system/s is the subterranean heating and cooling system. But that wont be possible to do on a rooftop, so your likely going to need a lot of air conditioning. The other parts to my greenhouse cooling include shade cloth covering to reduce solar gain, swamp coolers, and a portable AC system as a backup on hot days.

Using swamp coolers can be tricky in an enclosed greenhouse because that will raise the already high humidity. Typically commercial greenhouses use cross ventilation. Running the hot dry outside air through the swamp cooler pads, blowing it across the plants to the other side of the greenhouse, and out vents on the other side. In my greenhouse the subterranean system acts as a large dehumidifier, and will circulate the entire volume of air in the greenhouse 5 times every hour through it.

If you can build your greenhouse tall enough, some commercial greenhouses create a cooling atmosphere above the plants. Basically it consist of running a shade cloth screen across the inside the greenhouse above the plants. and using a fine misting system above it to create a large cooling zone. Of coarse it would need good air circulation through your greenhouse, and to be able to get as fine of a mist as you can.

I know you plan to use the poly plastic film for greenhouse covering. I'm using that as well. I don't think they make it thicker than 6ml, and that is what I'm using. I'm not sure if your using the construction poly or greenhouse poly. But I suggest using greenhouse poly with UV inhibitors. It will last more than a year, and help reduce solar gain somewhat. This is what I got Standard Clear Greenhouse Film, 6mil. Now when it comes to poly plastic film greenhouses, you can use either a single wall, or a double wall construction. I'm using a single wall. But double wall will insulate from outside heat much better. Basically a double wall uses a air blower that forces air in-between the layers to create an air pocket between the inside and outside layers. You can even get double wall poly plastic film so you don't need to drape it over twice, or need the spacers.

In my opinion I would drop the idea of using the angle iron, it will bend and twist way too much. You would need so much of it to make a sturdy greenhouse you wouldn't be saving anything. Round tubing, or wood framing are the only two strong main framing construction methods. I'm using a combination of wood framing and 2 inch round electrical conduit. The electrical conduit is much cheaper than the 2 inch metal fence post tubing, not to mention easier to work with. Unlike PVC tubing, electrical conduit is designed to be used above ground and resist degrading from UV. I used 3 inch deck screws to attach the 2x4 framing to the electrical conduit. All in all we have already had many strong windstorms, including a good hail storm, and my greenhouse barley even moves at all in the strong wind, and the hail didn't do anything to the poly film. I also attaches the poly film to the greenhouse using Lath screws (because they have washer like heads), and polyethylene Batten Strips. I got the 1,500 foot roll and used the heck out of it, covering everything. Both before and after installing the poly film. I still have about 25% of it left. It's important to get the poly film tight, if it's loose and flaps in the wind it can tear.

You'll need to register as a forum user to be able to see the pictures, but if you do you can see all the pictures of my greenhouse construction in this thread: Greenhouse construction begins in another forum. Starting from before I even began dinging, right up until last week or so when I first ran water through all 3 levels of hydro systems. I'm in the presses of fixing some leaks right now, and hope to have everything running leak free in about a week. When I do I'll post another update. There are literally 100's and 100's of pictures of the whole construction process, and I go over all my trial and errors both good and bad.

I almost forgot to mention, along with shade cloth to reduce solar gain, there is something called Shade Paint. It comes in a concentrate, you thin it out up to a 1 to 8 ratio, and paint it right on the poly plastic film (or any greenhouse covering). Just like shade cloth it reduces solar gain from UV inside the greenhouse. It's also biodegradable. Depending on weather conditions it typically wares off in a few months. That way during winter when you want all the light and heat you can get, it dosen't interfere. It's also relatively cheep (if you can get it locally and don't need to pay for shipping), running around $22-$28 a gallon depending where you get it. Here's a link to the stuff: Kool Ray Classic Shade

    Bookmark   April 6, 2012 at 4:43AM
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Dear Horehydro,
Thanks a lot for the brief comments. The system that you are construction looks very nice but for being at rooftop it will be not practically viable for me. Anyhow i will keep eye on it for my ultimate understanding.
I have given up the idea of using Angle Iron after your comments.

Note: RoofTop hydro plan was my first & last hydro setup until now & I have to shift this kind of hydro setup in my greenhouse too with some changes i have discussed in other post. I will continue with four setups like this in my first greenhouse experience. Thus i am new to hydro yet.

Now i am going to construct wooden structure finally that will be some what like this:

Anyhow, Fighting with Summer heat also will be the challanging issue for me to over come.

Doors at both side, three roof ventelation windows, two exhaust fans at one endwall of the greenhouse & two air inlet windows at the other endwall will be used for cross ventilation.

Shade cloth under the roof but over the plants will be used IF NEEDED.

I have planned to use Double Poly Transparent 6mil polyethyelene sheet all around the greenhouse including top. I can get construction poly easily but will give priority to find greenhouse poly. One sheet will be installed with in the inner side of the whole structure & the other will be outside of the greenhouse. The gap in between both sheet layers will be about 4-5 inches. Each sheet will be 6mil 150-160 microns thickness.

I have searched the web a lot & every where i have read that Double Poly Sheet that makes air pockets between them retain heat within the greenhouse & reduce heating costs about 50% compared to single poly coverings.
So how would i be able to use it. As i have to fight against high temperatures. Maintenance of a winter temps are not a problem at all & i am using no heating component or ant thing like that for it.

Please inform in detail how can i use double poly sheets adversely to cool down the greenhouse in high summer temps? Have you any design or so?

Since there is a 4-5 inches gap in between both poly layers I thing i wouldnot need a air blower to inflate polys. What you say? Am i right?

Have you tried or seen some plan please share with me.

I want to know the link & name of software you are using to create 3D images. I want to download it to make someone understand what i mean.

Please reply. Awaiting.

    Bookmark   April 7, 2012 at 9:03AM
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I have had a lot of things going on today, and want to give the reply due attention. So I feel it would be better to reply tomorrow night. Otherwise I would probably miss/skip points in an attempt to save time. But I think I may have misunderstood a important point. Is the greenhouse intended to be on a rooftop? Or did I misunderstand?

I do have a lot of greenhouse designs, construction methods, typical cooling and heating system designs I can post. I've been researching the subject for about 2 years now (well over a year before I started construction on mine). I don't think I know anything about your situation (planed greenhouse location), just that it gets hot and/or windy.

    Bookmark   April 8, 2012 at 6:29AM
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Dear HomeHydro,
Thanks a lot again for the ultimate attention.
yes, you can have your time & reply in details.
Yes, the Greenhouse will be on the rooftop. The pictures of bitter gourd that i have posted were also at RoofTop. It is the same elevation where i have to construct Greenhouse & it is about 36 feet high from ground level.

Yes, my area is very hot.
Outside day time temperature reaches 45-50 maximum in summer & there are about seven & half months of summer.
Outside day time temperature lowers down upto 0-5 in winter & there are about four & half month of winter.
There is no high humidity issue in our area.
Rain fall is average.

I have to place four bitter gourd type setups of pictures i posted earlier. I found this setup ideal & convinent in my case in greenhouse. One for cucumber, 2nd for tomato, 3rd for bitter gourd & fourth will be of any other gourd crop.

If you need to know any thing else please let me know.
Best regards take care.

    Bookmark   April 8, 2012 at 8:06AM
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That is one great looking greenhouse. Is there a web site I can download the plans from?

    Bookmark   April 8, 2012 at 10:45AM
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Yes here it is as under:

Here is a link that might be useful: Website

    Bookmark   April 8, 2012 at 11:32AM
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Hello azee_2009,
OK I originally thought it was going to be a rooftop greenhouse, but after rereading your second post I wasn't sure anymore. As far as the construction I used to build mine, it could be applied to a rooftop situation. By just building a sturdy base for the electrical conduit posts/poles. Similar to the baseboards I made for mine. The weight of it will keep it in place. The poles for my greenhouse only go down in the ground about 8-10 inches, and there is no cement holding them down (just the weight of the greenhouse structure itself). I just posted the link/information to give you some ideas.

That greenhouse looks much nicer than the one I built. Although much more expensive too. Not including the subterranean system, and the hydro systems inside, I built my whole 10 by 20 foot greenhouse for about $800. Ya, heat will be challenging. Our outside temp today was about 92 degrees, but the temp inside the greenhouse was 108 degrees. When the temps here reach the 120 mark, greenhouse temps would likely be around 140-150 if I didn't have a multi tiered cooling plan. Cross ventilation is great in some circumstances, but it wont help much at all to blow 120 degree air on your plants when it gets hot. Given the best circumstances, swamp coolers may bring the temps down about 20 degrees. But if humidity isn't carefully controlled, they may only provide a difference of between 5 and 10 degrees at most of cooling effect by themselves.

Just to clarify, when I mention high humidity, I mean in the greenhouse. That will depend a lot on temperature inside the greenhouse, water vapor given off from the hydroponic systems inside. Not to mention the biggest factor, how many plants your growing, and how big they are. Plants breath out water vapor (called transpiration). The water vapor (relative humidity) in the greenhouse will get higher and higher unless it's ventilated. But ventilating a cooler greenhouse with the (hot) dry outside air will only heat up the inside of your greenhouse.

I have searched the web a lot & every where i have read that Double Poly Sheet that makes air pockets between them retain heat within the greenhouse & reduce heating costs about 50% compared to single poly coverings.
So how would i be able to use it. As i have to fight against high temperatures.

The air pocket in-bitween the two layers of poly is an insulation pocket. Air pockets are the best insulation there is. Insulation will protect against heat just as easy as it does against cold. If your greenhouse is cooler than it is outside, the insulation (air pocket) will help keep your expensive cool air inside the greenhouse stay cooler longer. If you have no way to cool the inside of the greenhouse, then it wont help much. The air pocket is just insulation, not a cooling or heating layer. It just helps block the heat transfer from one side to the other. Blocks heat from getting out during winter, and blocks against heat from getting in during summer.

The 4-5 inch's between both layers you describe should be plenty. Typically it's only about one inch between layers. Though I would expect that you will still get much better results with a air blower between the two layers. The reason is if you blew the cooler air in between the layers, it won't give the air pocket a chance to heat up. Thus keep the heat transfer between the inside, and outside layers to a minimum.

I want to know the link & name of software you are using to create 3D images. I want to download it to make someone understand what i mean.
I use a free program called Google SketchUp. They have a pro version you can pay for, but I've always used the free version, and like it very much. I save all my drawings into a folder so I can expand on them later without starting over. Before you post your drawings, you'll need to remember to export and save it as a 2D image. Otherwise it wont be in jpg. format, and people that don't have Google Sketchup wont be able to view it.

Before I built my greenhouse, I did a lot research online to figure out what would work the best for me, as well as my budget. Here are a bunch of the links I have got bookmarked from those searches. I know it's a lot to read over, and it's been a long time sense I looked through it myself. But a lot of it is in lists of topics. I just read through what was of interest to me.

Arched Greenhouse
Horticultural Engineering
Greenhouse Energy Cost Reduction Strategies
Chapter 11- Greenhouse Site Selection
Chapter 12- Greenhouse Structures
Chapter 13- Greenhouse Control Systems
Chapter 14- Greenhouse Energy & Resource Alternatives "Greening" the Greenhouse
Greenhouse Glazing
Greenhouse Energy Conservation Strategies
Greenhouse Energy Conservation Strategies: Temperature and Scheduling
Managing Greenhouse Temperature

    Bookmark   April 10, 2012 at 6:55AM
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Hello HomeHydro,
How are you doing?
I am working on design & revert back to you after making a sketch for your kind approval. Please be patience, i shall be back with in one or two days after uploding sketchs for your approval. My ameil id is
gejaangee at y0hu0 .c0m . Can i have yours?
Best regards

    Bookmark   April 11, 2012 at 3:21PM
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Hello azee_2009
First I would like to say you don't need my approval for anything, I'm just a guy that try's to help when I can. You can build your greenhouse any way you wish. I just wanted to post my experiences, as well as the information I've found along the way in the process of looking into the options that would suet my needs best. With that said, I would be happy to look at anything you would like me to view, and I'll be happy yo give you my opinion and reasons for them. But in the long run it's your money/budget, time, situation, and your the one that will have to look at it every day.

I'm not really sure what this: "My ameil id is
gejaangee at y0hu0 .c0m means for sure, but I think you mean to give your e-mail. I have many e-mail addresses, and one specific for posting when I know it will result in getting spam. You can reach me at:

That's my junk e-mail, but I can reply from one of my regular e-mails later. Just title e-mail "azee_2009, Greenhouse construction" Also try to e-mail me soon. I get 50+ spam messages a day in that inbox, and just cant spend the time to go through it all looking for one message. I just deleted every message there so I won't have a lot to look through (for a few days anyway).

If you send me drawings, send me both the 2D image, as well as the original skp. (Google program) drawing. I have the program, so I'll be able to open it.

    Bookmark   April 12, 2012 at 4:17AM
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Dear Homehydro,
My email id is
I have send email to you.
Please check them number wise & by dowloading in to a seperate folder & examine them by zoomimg images.

Looking forward for your co-operation.

    Bookmark   April 14, 2012 at 11:47PM
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I got the pictures, give me a few days to look them over. I have a few questions for you now though.

1. Where do you live (country, state, region)?
2. Do you have a specific budget, and have you looked into the cost of the materials you plan on using?
3. Do you own the property the greenhouse is going on?
4. Is this greenhouse meant to be a long term permanent structure, or just meant to last a few years and/or removable if you move.
5. Are you aware to get the power you will need, you'll need to have someone add breakers to your breaker box, as well as run the lines to the greenhouse, and outlet boxes?
6. Is the greenhouse an investment? That is, are you looking for increased property value once it's built.

    Bookmark   April 15, 2012 at 5:10AM
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Dear Homehydro,
Thanks for the contact.
1: I live in Gujranwala city, Punjab province, Pakistan.
2: Yes I have an idea, how much budget i will need to buy material. But i will still refrain on spending more & more budget. I am not going to use air conditioners or humidifiers or so as electricity breakdown is problem for me. Anyhow i will have UPS as a power backup for all appliances in greenhouse. The electircal components i am going to use are not going to be waste in anyway but i have several uses if any extra component is going to be useless in greenhouse afterwards. I will make another thing from it. I like DIY projects. All components from my previous RoofTop structure is still in my other use.
3: Yes, property is our family property & my father own it by name. We are not shifting somewhere else.
4: Yes, it will be permanent structure as long hydro outputs are more than inputs.
5: Yes i am aware about the power i need. I have an expert electrition in hand for breakers or so etc.
5: No, its not an investment, I want to grow for my family consumption as well as for my guests.
I have still to proof the dignity of Hydro before my family. I am failing to proof until now. But i have seen no drawbacks in my previous hydro setup & i will make same setup with in the greenhouse too. I am not looking for increased market value once its built.
This is my website & i do seed business in Pakistan.
Best regards & looking for your reply.
Take care.

    Bookmark   April 15, 2012 at 8:18AM
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