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JDW's DIY Greenhouse Plan

Of course we all want a greenhouse, but for some of us a prefab kit just won't do. I always try to DIY whatever I can to save money, because I can tailor it to suit my needs, and it usually costs a lot less. After reading a bunch of books and spending hours (days?) on the internet I've came up with a plan I want to show you all.

This greenhouse is 12 feet wide and 16 feet long, with the peak running East-West. The top of the peak is 12 feet from the foundation. The two ends (West and East sides) are walls out of 2x6 pressure treated lumber, studs spaced 24" on center, with exterior grade plywood skin on the inside and outside. Although the East side would only have plywood 3 feet up, the upper part would be glazed to let in morning sun. The ribs along the North and South sides are either 3/4" EMT metal conduit, or 3/4" PVC pipe. The length of each rib is ~14' with a radius of ~14.5'. I think I could attach the pipe to the wood frame with angle irons bent to the right angle, with the pipe slipped over it? The South face would be skinned with a double layer of poly inflated with a fan. The North side I want to skin with something opaque and insulate. I also want to insulate the bottom 3 feet of the East and South sides. I don't know what I'd use to insulate the curved walls.

First pic, view from the Southeast.
GothicSW.jpg


The white rectangle above the door is the vent. I need to frame out a spot for the exhaust fan on the other side once I determine what size fan I need.

Second pic, birds eye view, northish.
GothicUp.jpg


The white space is all fixed benches, the red space is a movable bench, if I can figure out how to do that. The green box is an aquaponic system. And the orange cylinder is a water heater. I haven't ran the numbers to see if I could heat it with a household water heater, but if I can I could run hot water through the floor of the greenhouse.

Third pic, South view.
GothicS.jpg


Fourth pic, East view.
GothicE.jpg


The big blue boxes are water storage tanks, maybe. Originally I made plans for a conventionally shaped greenhouse with gutters to collect rainwater, but with a greenhouse this shape I don't think that would work. My tap water is very hard so I would have to filter and treat it to make it suitable for the things I'm growing, or use RO or rainwater. Watering out of tanks inside the greenhouse would have the benefit of storing heat, and the water wouldn't be cold going on the plants. The benches will sit on top of 55 gallon drums filled with water, for heat storage.

Areas: insulated - 433 ft[SUP]2[/SUP]; double wall polyethylene - 160 ft[SUP]2[/SUP]; twin wall polycarbonate - 59 ft[SUP]2[/SUP]
Volume: 1522 ft[SUP]3[/SUP]
Using a $2 price per gallon for LP gas, a minimum inside temp of 65[SUP]F[/SUP], and avg outside lows for Mishicot WI 54228, I calculated this greenhouse would cost around $500-800 to heat over the winter. That's not counting any heat storage, or night-time insulation over the glazed areas.
The fixed benches equal roughly 70 ft[SUP]w[/SUP] and the movable bench 24 ft[SUP]2[/SUP].
If a 16 foot treated 2x6 costs $8.50 and a 10' long 3/4" conduit pipe costs $3.30, the greenhouse frame would cost just $200. Plywood would add about $125. Then gotta add glazing, insulation, heater, etc etc. I might be able to build this for less than a grand?

Things I'm not sure about:
Would I have to brace up the East and West walls?
How to attach the poly to the wood frame?
How to attach the exterior siding on the North side?
What insulation would I use on the North side, and the bottom of the South side? Spray foam insulation would work best but cost effective?
What to do for a foundation? Was thinking of a 12'x16' frame of 2x6's with 4x4 posts at each corner and every 4 feet on the sides.

So what do you think? I know I still have a lot of work to do yet.
 
Looks cool! but..what do you want it for? what do you plan to grow in it?
For the vast majority of Americans, greenhouses simply aren't practical..
They are useful in March, where they can create an "early spring" as opposed to outdoors.
and they could be useful in October, where they can extend the growing season by a month or so..
For the remaining 10 months of the year, there isn't much you can do with it..
its FAR too hot in the summer, and much too cold in the winter..

Greenhouses are common in England, where the year-round climate is much more mild..
a 30 degree frosty winter day outside the greenhouse becomes a 50 degree day inside..that is actually practical and useful.
but when its 10 degrees outside, being 15 degrees inside the greenhouse isn't any benefit..its still cold.
and in the summer, 80 degrees outside the greenhouse is *much* better than 100 degrees inside the greenhouse..

If you can afford the heat in the winter, then more power to you! ;) Could be good for overwintering VFT's and Sarrs I suppose,
if you can keep it nicely above freezing..expensive, but certainty doable..(there are a lot of cheaper ways to do VFT and Sarr dormancy however! ;)
Probably wont be able to keep nepenthes in it all winter though..
and you probably wont want anything in it in the summer..

So, let us know what you plan to grow in it! ;)
thats makes a big difference..

Im not saying you shouldnt do it..im sure it can be fun if you are really into it..
but for most people, a greenhouse is not only impractical, its often actually *worse* for most plants than being outside..
its just the nature of our climate..too hot in the summer, and too cold in the winter..

Scot the realist..(sorry to rain on your parade)
 
Scot the realist..(sorry to rain on your parade)

Haha, no problem Scot. This greenhouse would be more for orchids than CPs. My small orchid collection is outgrowing it's 3x2x4' grow chamber I made a few months ago. I want to start breeding them and that's also going to take a lot more space. The CPs that I want to grow would mostly be lowland/intermediate neps, some sundews and a few others. I hope to produce a few plants to sell, hopefully enough to pay for most of the operating costs. I might also give a little space for fresh food during the winter. This greenhouse would still be a little small to go far with all that going on, but it's what I'm looking at for now.

A greenhouse, even one this small, is a very expensive endeavor, but I think it's the most cost effective solution for me. To grow the same amount and types of plants indoors, under artificial light, would cost about the same, take up room I don't have, and create problems with water and humidity. My greenhouse would have more surface area that is heavily insulated compared to the area that is glazed, so would lose much less heat in the winter than a conventional greenhouse, like the prefab kits on the market. This, together with lots of water volume for storing heat from the day and releasing it at night, should cut heating costs to a level that's acceptable for me.

As for cooling, since the South face glazing is polyethlyene plastic, I will remove it during the summer months. I can replace it with a shade cloth, which will cut heat gain and light levels that would be too much for the plants anyway. Plus misting and fans for evaporative cooling and I should be able to keeps temps in the safe zone.

Someone pm'ed me and suggested I build it pit-style. Since I'd be insulating the bottom three feet of the wall, I could dig the floor three feet down. The earth down there (well below the frost line) stays around 45-55[SUP]F[/SUP] so would provide heat in winter, and cooling in summer. But I'm not sure if I want to dig a big hole in the yard. It's likely I'll move in 2 years or so, and that would create problems when I take down the greenhouse.

Thanks for your input Scot! I appreciate any help I can get with this crazy project.
 
RL7836 pm'ed me with some good questions, he said I could share this:
RL7836 said:
Very interesting design - I'll be following your thread closely. Most people skimp to save on upfront costs and then get killed with the real money areas - operating costs. You seem to be considering those as well but I would try to get as much input from people who run greenhouses in similar climates as possible (Tony P. being number one - he's in upstate NY).

Some thoughts

- you use 65*F for winter operating minimum? Is that realistic? Is it necessary for the plants you'll be growing? I'd consider running the numbers for 50 & 45*F
- consider what plants you'll really want to grow - HL, LL or intermediate. Trying to grow both HL & LL in same space can be tough.
- you've considered winter heating - what about summer cooling. Depending on the types of plants - exhaust fans may not be enough (swamp cooler?)
- back up systems or at least alarms that will page you if your systems crater. Depending what you have inside, this could save a lot... (Michael Catalani has some good info on his setup on his site).
- have you considered a pit greenhouse (depending on your site)? Having the lower ~3' sunk into the ground can help a lot in both summer & winter.
- have you looked into misting & sprinkler systems?

Good luck with your endeavor...

Just so I don't have to type it all again I'm just going to copy my reply:

"1. I will actually be growing orchids mainly, and 65 is a safe bet. I might be able to get away with as low as 55.
2. For neps I'm mostly looking at LL/Int. I have a small grow chamber in the basement for HL if I really want them.
3. During the summer I was planning on removing the polyethylene covering on the South face, and replacing it with a shade cloth. Also plan to put mist nozzles on the HAF fan for a little evap cooling. Not sure if this will be enough but adding more shouldn't be too hard.
4. I will get a controller/monitoring system of some sort, possibly build my own Arduino based controller. Not sure if this is feasible, but I thought of putting a webcam or two in the GH and hooking up some sprinklers to solenoids that I could control over the internet. Then I could view and water my GH remotely!
5. Actually sinking the GH 3' was my original plan, but since I'll likely be moving within 2 yrs I wanted to build something I could take with me and didn't leave too much of an impact on the land here, it's still an option though.
6. No but I plan to have some mist/sprinkler thing going on."
 
I think I might be worried about wind loading on those tall sides.
 
I think I might be worried about wind loading on those tall sides.

I am. I'm worried that the structure won't be stiff enough, and would fall over to the East or West. Currently the East and West end walls would only be held up by the ridge beam, the glazing, and the attachment to the foundation. I'm not sure this is enough, or what I would need to add to fix it...
 
Haha, no problem Scot.
*snip*
Thanks for your input Scot! I appreciate any help I can get with this crazy project.

ok! cool..sounds like you know what you are doing, so thats all good then..
(sometimes you cant tell if someone is a newbie who wants a greenhouse just because they think it would be cool, but doesn't really understand the ramifications..
or if someone is a more advanced hobbyist who knows the pros and cons, and is choosing to build a greenhouse because it will actually work for them..)
we can see now you are in the latter group..so, carry on then!
icon-cheers.gif


Scot
 
Because of all the problems/unknowns in the gothic GH plan, I'm drawing up some different options and see if I can come up with something better and less worrisome. The main reasons: A. want more growing space/ better utilization of space, B. doesn't seem strong enough, must resist high winds and snow, C. hard to insulate curved wall as much as I need, D. not enough water storage. So now I'm leaning toward a more permanent structure of wood, maybe sunken 3 feet with a cinder block foundation.

Can you change a threads title?
 
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!
 
  • #10
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.
 
  • #11
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 :).
 
  • #12
...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.
12x21CBfoundation.jpg

12x21CBframed.jpg

12x21CBframed2.jpg

12x21CBbenched.jpg


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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