Gonmon's DIY Greenhouse Plans

[Gonmon]

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.

It would be mainly for orchids (Stanhopeas, bulbos, mini-catts, etc.) but I also grow carnivorous plants, tropical fruits, and maybe some fresh veggies for winter. I want to start breeding and need more space for large stock plants and raising young plants than I have room for indoors.

Unfortunately I can't seem to get my images inserted... so they're attached. First pic Southeast view. 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 sqft; double wall polyethylene - 160 sqft; twin wall polycarbonate - 59 sqft
Volume: 1522 cuft
Using a $2 price per gallon for LP gas, a minimum inside temp of 65F, 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 sqft and the movable bench 24 sqft.
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.

[WhiteRabbit]

Very cool! Sorry, I can't answer your questions - I bet someone else will be able to, tho. Good luck, and let us know how it progresses, please!

[DavidCampen]

Do you think this is going to be sturdy enough to survive more than a year or two? What happens in the winter if your power fails and thus the fan inflating the south wall fails. What is your ridge board made of?

[spetrizio]

I am not sure, but I think it is too light construction.

[Gonmon]

Originally Posted by DavidCampen

Do you think this is going to be sturdy enough to survive more than a year or two? What happens in the winter if your power fails and thus the fan inflating the south wall fails. What is your ridge board made of?

I have no idea how much integrity the inflation of the poly would add to the structure. The north wall's siding would add a little, but I can't see that the north and south sides are really a significant factor in the strength of the building. The ridge beam is just a 2x6. IMO that's inadequate, but I have no idea how to tell either way.

Originally Posted by spetrizio

I am not sure, but I think it is too light construction.

I do too... Because the only thing that would be holding the building together is the attachment to the foundation, and the ridge beam. This plan would need some diagonal braces and such.

I'm certainly not an architect, and don't really know where to start to determine whether any structure I plan is structurally sound or not. So I try to overbuild things when I can. This plan was a shot at paring it down as much as I could, to make it cheaper and more mobile.

But now, my dad has suggested a few spots where he'd be ok with me digging the GH down in the ground. The spot I like it might be hard to get utilities to. So I'm looking back at some plans for a sunken GH and see if that's possible.

[DavidCampen]

I would suggest that you build a full wood frame as the basis for your greenhouse and then cover it with whatever materials that you can afford. How big of a structure can you build without a permit?

Ortho Books publishes a book of greenhouse design, it would be a good resource for you.
Amazon.com: All About Greenhouses (Ortho's All about) (9780897214636): Ortho: Books

[Gonmon]

I don't think I will build this gothic style greenhouse. I'm just too unsure on how strong the building would be.

Originally Posted by DavidCampen

I would suggest that you build a full wood frame as the basis for your greenhouse and then cover it with whatever materials that you can afford. How big of a structure can you build without a permit?

Ortho Books publishes a book of greenhouse design, it would be a good resource for you.
Amazon.com: All About Greenhouses (Ortho's All about) (9780897214636): Ortho: Books

I am working on a plan for a wood frame greenhouse right now (plus like 5 I made before ). Debating on whether sinking it 3 feet with a cinder block wall to ground level would be worth it. I have to check prices and figure out how much that would cost. Otherwise I'd put it on a 3 foot kneewall, fully insulated. But I don't know how I'd make a foundation for that. And then I'd have to dig down around the perimeter to insulate the earth.

I've found that most greenhouse references don't help me much in designing my greenhouse. I'm working on a solar design principle with a South wall at 30 degrees to vertical, to let in the most of the winter sun. The North and West walls 6" thick and heavily insulated, and the East wall glazed with polycarbonate to let in morning sun. I bought two solar greenhouse design books, and rented a few general construction books from the library.

I hadn't called the local building inspection office yet . I looked for the number today and couldn't find it, so called the town hall and left a message. But in a city near me you can build a greenhouse up to 25,000 cuft without a permit. I might need a permit for modifying my (well my parents') houses' electrical, LP, and water systems though.

You can't change a threads' title after it's been made huh? Maybe I should make a new thread "John's giant thread of Greenhouse Ideas"..........

[DavidCampen]

You really should look at the Ortho book. It has a lot of good structural design information. I bought mine at an Orchard Supply Hardware chain store.

[Gonmon]

I'll have to track one down then. I see Amazon has them for $10 + shipping.

[Gonmon]

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...