JDW's DIY Greenhouse Plan

[JDW]

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.


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.


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.


Fourth pic, East view.


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 ft²; double wall polyethylene - 160 ft²; twin wall polycarbonate - 59 ft²
Volume: 1522 ft³
Using a $2 price per gallon for LP gas, a minimum inside temp of 65^F, 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^w and the movable bench 24 ft².
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.

[scottychaos]

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)

[JDW]

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^F 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.

[JDW]

RL7836 pm'ed me with some good questions, he said I could share this:

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."

[Rocketcaver]

I think I might be worried about wind loading on those tall sides.

[JDW]

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...

[scottychaos]

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!

Scot

[JDW]

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?

[lance]

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!

[JDW]

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.