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Thread: JDW's DIY Greenhouse Plan

  1. #9
    Class 5 Nepenthes hoarder lance's Avatar
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    Yeah, you'll certainly want a good foundation for the GH. While your design is susceptible to wind, the high roof ratio would be great for the snow as it would just slump off from the roof being so steep. I put my GH on a foundation which has certainly helped with the wind problem. If you experience 50 MPH or higher wind then I would recommend bracing the east and west walls. To insulate the curved sides I would recommend using that plexiglass stuff with air pockets inside of the two layers. What type of orchids will you be growing in there? This will depend on what Nepenthes should grow in there and what cooling/heating systems you should have. Keep in mind that lowland Nepenthes will slow down considerably in the winter if the temps inside aren't at at least room temperature at night. Of course, there are some tolerable hybrids that can grow fast and good for you year round. I wish I knew more on the topic, but I have only assembled a GH once and that was years ago for my Lowland Nepenthes. The moderators can change the thread title if you ask them here. Hope this helps!


    In addition to growing plants, I design and build RC planes powered by Tesla batteries. Check out my progress at www.chargedplanes.com

  2. #10
    JDW's Avatar
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    Quote Originally Posted by lance View Post
    Yeah, you'll certainly want a good foundation for the GH. While your design is susceptible to wind, the high roof ratio would be great for the snow as it would just slump off from the roof being so steep. I put my GH on a foundation which has certainly helped with the wind problem. If you experience 50 MPH or higher wind then I would recommend bracing the east and west walls. To insulate the curved sides I would recommend using that plexiglass stuff with air pockets inside of the two layers. What type of orchids will you be growing in there? This will depend on what Nepenthes should grow in there and what cooling/heating systems you should have. Keep in mind that lowland Nepenthes will slow down considerably in the winter if the temps inside aren't at at least room temperature at night. Of course, there are some tolerable hybrids that can grow fast and good for you year round. I wish I knew more on the topic, but I have only assembled a GH once and that was years ago for my Lowland Nepenthes. The moderators can change the thread title if you ask them here. Hope this helps!
    Ya a gothic shaped greenhouse would shed snow just fine. I live on a hill, and just a lil bit from Lake Michigan, so most days winds are 15-30mph. Ocasionally we get nasty days with gusts up to 50. The twinwall plexiglass would work on a curved surface, it's flexible, but the R-value is only around 1.8. I'm looking to insulate the North wall to R20, 6 inches of fiberglass batting. The problem is that fiberglass loses its insulating value when wet, I haven't come up with a good way to make a durable, watertight, curved wall that I could attach to the EMT pipe ribs.

    I grow a bit of everything, but want to focus on breeding mini-cattleyas, stanhopeas, and bulbophyllums. They require temperatures 50+, and grow best when nights don't drop below 60. This plan for a gothic style greenhouse has 59 sqft twinwall polycarbonate (East wall) with a R-value of 2.2, 160 sqft of inflated double wall polyethylene (South face) with a R-value of 1.5, and 433 sqft of 6 inch fiberglass (North and West walls) with R-value of 20. I calculate the heat loss for January (avg low 14F) with inside low temp 55 degrees would be 7,300 BTU/hr. So I'd need a 10,000 BTU heater. Most home water heaters are around 30,000 BTU.

    For cooling, I can remove the double poly wall and replace it with a shade cloth when outside lows are above 55 degrees, which is June-Sept for me. Avg highs then are about 80 degrees, but we usually get weeks at a time that are 95ish (like all long this summer, ouch!). With shade, misting, and ventilation I ought to be able to keep temps in the 80's.

    So what size was your greenhouse? You don't have it anymore? What foundation did you use? I know how to do a cinderblock/concrete foundation, but I'm guessing it would add at least $500 to the cost. If I didn't do that, I was thinking of burying 4x4 posts at each corner and every 6 feet on the sides, 42 inches deep (frost line up here) with poured concrete footings. Then putting a 4x4 frame the same shape of the base of the greenhouse on top of the posts. I don't know if 4x4s would be enough, or if I would need 6x6 posts. I've never built a wooden foundation and can't seem to find much info on it.

    I hope that answers your questions. I really appreciate the help from everyone. This isn't something I'm rushing into and every bit of information and experience you guys send my way helps me refine my plans. I'll see about changing the thread title and posting up my new ideas.

  3. #11
    Class 5 Nepenthes hoarder lance's Avatar
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    Yeah then I'd suggest getting some intermediate hybrid crosses between lowlanders and highlanders for Nepenthes. Theres some very nice ones out there. I use a 5.5 GPH RO unit which supplies all my plant water and does just fine with the mist system. The only problem is the amount of pressure you need to make the misters actually mist instead of drip. For that I use a 3/4 Horsepower industrial pump. You will probably want something with a little more kick (5-8 horsepower) since your GH is bigger then mine and it's higher. You can find a misting hose easily online, they're the ones used to cool down patios/shops. My GH is a small GH that I still have (6' 6' 7'). It's such a small GH all I had to do was get 4 giant drill bits and drill into each corner of the GH (there was cement below which used to be from an old basketball court). I'm not really very experienced with foundations myself. I think your fine with the depth part of it though... you'll need that with the high winds you receive.

    For the misting part of it you all probably be best off if you attach it to the top of the inside of the greenhouse and stretch the misting hose along that 2 by 4 (or is it a 2 by 6?). That should work the best for the cooling methods since hot air rises. Can your orchids take to temperatures above 95*F? I grow a few highland orchids which don't seem to mind the high temps it as long as their temps don't get below freezing.
    If not then your probably going to want to think about other cooling options. A radical Idea I just stumbled upon a while ago involved a guy with a 10000 foot square GH who buried about 100 feet of large pipe about 5 feet below the ground and sucked air through it to cool his GH. This may require some calculations and a backhoe to dig up the ground to put the pipe in. You would probably want 1' diameter pipe (drainage pipe, not the PVC kind) which can be bent in a circular-like pattern in the pit dug by the backhoe. I have some of it which is used for drainage. It's not that expensive based on what I saw the gardeners install for the drainage. There was a video on youtube of it somewhere, but I can't find it. Also, if your gonna have exhaust fans then it would be a lot better if they were closer toward the ground to pump the cool air in. This would be more effective. You will also need a vent which could go right in that white box above the entrance door. You may have to shorten the two wood triangles above that based on the dimensions of the vent, most vent systems are square. I'd recommend getting a vent with an auto-opener based on the temperatures so it opens when it's hot and closes when it's cold. The exhaust fan which will be blowing in the air would have to be somewhere closer to the ground where it could suck in colder air more efficiently. Also, you could always attach a underground pipe on the back of the fan from the "radical idea" above if time and money permit and if the calculations show a wide difference from the air entering the pipe into the ground to the air coming out of the pipe into the GH. Not a lot of people have done this "radical idea" which is why there isn't much evidence to show that it cools the air enough. Still, unless you want to buy a big industrial swamper it's probably the best way to go. The cheapo swamp coolers that are usually >250$ tend to break a lot even if they do a good job at cooling. It's too much of a risk. Theres several cooling systems above those prices if your willing to go that route, and I'm sure several forum members would be willing to show you those options if needed.

    I probably got carried away :P, but I hope this helps with the cooling option. In the end you'l be saving a lot of money on the GH, I've seen high prices for custom-made GreenHouses that go in to the 10's of G's. If anything comes to mind I'll post it on here .


    In addition to growing plants, I design and build RC planes powered by Tesla batteries. Check out my progress at www.chargedplanes.com

  4. #12
    JDW's Avatar
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    Quote Originally Posted by lance View Post
    ...I use a 5.5 GPH RO unit which supplies all my plant water and does just fine with the mist system. The only problem is the amount of pressure you need to make the misters actually mist instead of drip. For that I use a 3/4 Horsepower industrial pump. You will probably want something with a little more kick (5-8 horsepower) since your GH is bigger then mine and it's higher... My GH is a small GH that I still have (6' 6' 7').

    ... Can your orchids take to temperatures above 95*F? I grow a few highland orchids which don't seem to mind the high temps it as long as their temps don't get below freezing.
    If not then your probably going to want to think about other cooling options. A radical Idea I just stumbled upon a while ago involved a guy with a 10000 foot square GH who buried about 100 feet of large pipe about 5 feet below the ground and sucked air through it to cool his GH. ...You will also need a vent which could go right in that white box above the entrance door. ...I'd recommend getting a vent with an auto-opener based on the temperatures so it opens when it's hot and closes when it's cold. The exhaust fan which will be blowing in the air would have to be somewhere closer to the ground where it could suck in colder air more efficiently.

    I probably got carried away :P, but I hope this helps with the cooling option. In the end you'l be saving a lot of money on the GH, I've seen high prices for custom-made GreenHouses that go in to the 10's of G's. If anything comes to mind I'll post it on here .
    I have a 75GPD RO/DI filter for making water for my fish tank, so I might use that if I can find a way to get the water from the GH to my basement for the fishies (or buy another unit). I would like to collect rainwater off the roof of the greenhouse, into water tanks inside. How much volume/hour or minute does you mist system put out, or what nozzle do you have? I haven't looked at water pumps for misting, but 5-8 hp seems a bit much.

    All my orchids are warm or intermediate growers, they can handle 95*F fine. The geothermal cooling thing isn't something I would do. I don't feel that cooling will be an issue in the summer because outside temps are rarely above 100*F here, the South face will be open with a shade cloth covering it (so it will be a shade house not greenhouse), and I'll be installing a mist system. The white vent box is just going to be open. A 1'x4' plywood piece will be on the outside, and open and close via an automatic vent opener. The "solar" kind with a wax tube that expands/contracts with temperature. The exhaust fan will be pushing air out of the greenhouse, which is more efficient at cooling than pushing air into the greenhouse. That is why the fan is mounted high up. The fan will be controlled by a thermostat to turn on and off automatically.

    Aaaaand, here's my next plan!

    This is what I'm looking at if I sank the greenhouse 3' in the ground with a cinder block/concrete foundation, and a wood frame of treated 2x6's.





    This first pic is just the cinder block foundation. Second and third pics are with the wood frame. Fourth pic shows the bench layout.

    It would be 12' wide, 21.5' long, and 12' high at the peak. The North wall, roof, and West wall would still be insulated with 6" of fiberglass, the South wall glazed with double layer poly, and the East wall glazed with twin wall polycarbonate.

    I could fit 5 275 gallon bulk containers (big white boxes in second pic) for water storage, and one 330 gal for an aquaponic system for veggies. For a total water volume of 1600 gallons. The aisle down the center is 24" wide and the benches are 48" wide. Bench space would be 110 sqft on 210 sqft of floor space. There would be enough head room for two or three hanging basket lines.

    Why so much water? Because when one gallon of water cools off by one degree Fahrenheit it releases 8.33BTU (About Greenhouses: your greenhouse questions answered here.). If my 1600 gallons of water cool from say 70 in the day to 60 at night, it would release 133,000BTU, if I'm doing my math right.

    The foundation would need just over 300 blocks, which are $1 a piece. Plus concrete for the footings and filling the holes in the blocks. Plus rebar for strengthening. So I'm guessing it would be somewhere around $600-1000 just for the foundation. The wood for the framing would run around $400. Then I'd need glazing, roofing, siding, benches, 6 IBCs @ $75 a piece, insulation, heater, fans, etc. My guess is that the total project would cost $3000-4000.

    I didn't want to go over $2500 total cost for the greenhouse and all equipment. The biggest way for me to cut the cost would be to extend the walls 3' and put it on a wood foundation. This would sacrifice a little insulation value, but save $500. Another way to save some money would be to buy the materials used. So far there hasn't been much on craigslist...

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