Landscape-integrated greenhouse - so many possibilities!

9 years ago

So, I purchased a piece of land in the countryside in Iceland a year ago, and I'm looking to build a house and greenhouse there. The house has been stuck in all sorts of delays related to architects and approval, so I've been thinking more about the greenhouse lately and have some questions

Here's what I can say for sure. The purpose is to give a permanent year-round home to nmy tropicals. This being Iceland, it's fairly snowy, and *very* windy. Hurricane-force winds are an annual occurance. Last summer I had an empty multi-ton steel shipping crate on my land blown over seven times across flat ground - and summer is the least windy season. The location I want to build is a natural ravine. It starts at the north side of my land (zero depth / a couple meters width), and gets deeper and wider as it descends south into my canyon, opening up at its deepest perhaps 10 meters deep / 15 meters wide, maybe more. Bedrock is shallow - it's even visible on the surface on the south side. A small stream runs through the ravine, fed by artesian springs and seeps; in dry times it only begins halfway down, while in wet times it flows all the way.

I want to start with a structure closer to the shallower end - a roof across the ravine with two walls, no side walls or floor, so as to minimize heat loss and wind profile. I want to design it suchly that should I ever want more space, I just need to remove the south wall and build a new segment further down into the ravine where it's deeper and wider. The initial segment would be perhaps 3-4 meters wide and 5-10 meters long, depending on cost. The stream would be allowed to continue on its natural course; everything would be built around it. The stream is cold, so my plants would be in bottomless pots and raised beds, which I plan to cast out of hypertufa. I'm going to connect both electricity for wintertime lighting (I already own lots of lights, as I grow my plants indoors as-is) and geothermal hot water for supplemental heating (this being Iceland, it's readily available and affordable). I plan to plant a dense shrub windbreak upwind of the greenhouse to act as a wind-(but especially snow)-break.

My questions revolve mainly around glazing and construction.

I have experience with greenhouses, but only small kit greenhouses with film glazing (which I subsequently modified extensively to improve, but never anything on the scale of what I want here, a true permanent durable thing in a harsh environment). I've considered two main routes:

1) Buying a greenhouse - ideally, a disused existing one and recycling it, otherwise a new one - and adapting it to the landscape.

2) Building one from scratch.

I don't know which is the better option. I know how to weld, although I've never worked with aluminum (I want to use aluminum for durability reasons). I have a 12-ton pipe bender and a mig welder. I've never worked with concrete for anchoring the beams but I have plans to learn. I have a guy who operates an excavator for a very reasonable price.

I've never worked with permanent glazing panels (as mentioned, just plastic film) and thus have no clue how one works with them. I assume there's some sort of clips, but how do the panels attach to them and to the frame? What prevents airflow through the gaps between the panels? What sort of precision is needed on the frame alignment to work with panels?

And of course comes the obvious question, what type of panels - glass or plastic, and if so, which varieties? In terms of "used", I found, for example, a disused series of old commercial greenhouses around here with most of its panels broken, but there's still plenty left intact. I could maybe get them cheap or almost free. But then, I dont know why so many are broken. I know there were fires in the area, but the glass doesnt look blackened; if the panels are brittle, I wouldn't want to waste the time. But they could be perfectly fine, I have no idea. Glass in general seems to be the dominant greenhouse material here, but then again, it's also really heavy and kind of a pain to work with. Plastic would allow me to work with larger panels and thus less attachment labor, no risk of cuts, no risks of break during transport, etc. But it's also generally not considered very wind tolerant, and I imagine they're more expensive. Are there any sort of say polycarbonate panels that can actually withstand serious, even potentially hurricane force winds?

Then comes other questions. For example, what sort of rake should the roof have? High rake would be good for getting the snow to slide off and more height for my tropicals to grow, but a low rake would have a lower wind profile and heat loss and use a little less material. And maybe more of an arch than a perfect V so it's a little stronger in the face of wind?

And how to build it? I mean, I'm envisioning a lot of difficulty trying to work with panels or welding while hanging on for dear life to aluminum poles high up in the air. So I assume one would generally assume working with a scaffolding. But then I got to thinking, maybe I could make a tilt-up approach? I was thinking I could possibly get it fully assembled laying flat on the grounds with the top pole functioning as a hinge - the side poles not being welded directly to it, but to larger diameter pipe that can rotate freely around it - and then dragging the whole pre-assembled frame into position (panels and all already attached) and raising it with the excavator, with the side poles slotting into trenches on each side. Then it would just be a matter of getting up on a ladder and welding the "hinge" in a few places so that it can't rotate any more. Does that sound reasonable?

The foundation on each side: which sounds better, bare aluminum poles in the ground, or aluminum in concrete in the ground? Either way, I'd have the excavator bury then.

All of the other stuff: I'll obviously need doors, vent openers (are panels easy to hinge?), etc.

Last question: Am I stupid to think of doing this myself with a little help where needed rather than hiring someone? Because I'd really rather do it myself, if only for the accomplishment.

Thanks for whatever advice you can offer :)

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Comments (7)

Karen Pease
Original Author
9 years ago
last modified: 9 years ago
Been doing some more reading. As far as attachment goes, I kind of like the "slotted" approach; I could just build the frame with parallel I-beams and slot the panels straight into them, then seal around the edges. That sounds pretty simple, although of course sealing so much would take time.

I'm trying to get a handle on the balance between light transmission and strength (heat is secondary because, as mentioned, hot geothermal water provides cheap heating here - cheap, although still far from free). I've read that single pane 3mm single pane float glass has a light transmission of about 89%, and it barely declines at all with thickness. The allowable load for 3mm is about 1800N, 4mm is 2600N, 5mm is 3600N and 6mm 4400N. I imagine double-pane would be the same, relative to the thickness of each pane, and would have about 80% transparency. I found a polycarbonate supplier (Polygal) who has a variety of products (no single pane listed that I saw, all at least 2 panes). One can choose a balance between transparency and strength. One can get 80% transparency with 600N strength, 79% with 750N, 72% with 1550N, and 62% with 3350N. (On the upside, they all have much better insulation). Their graphs show that regular crossbeams every meter could get about 2 1/2 times better strength - but that would probably increase my materials costs by 50% and double my labour time. (On the other hand, I have no clue what sort of geometry those glass strength figures I saw presume...)

I assume any freebee/cheap glass I could get would be 3mm (I know it's single-pane, most greenhouses here use single pane). Really, the question is, how much should one worry about light transmission levels. And I suspect unfortunately that's a pretty big deal... We don't get a lot of high sun here, it's mainly low, and it varies so dramatically from season to season - 24/7 light in the summer, only indirect light in the winter.

Hmm, maybe I can find thick corrugated single layer polycarbonate somewhere, maybe that might outperform glass. Otherwise, based on what I've seen, I'm *thinking* glass is the better solution (to get high transmission with high wind tolerance), even though I don't like the thought of windblown debris taking out windows, or even just having to lift them...
Karen Pease
Original Author
9 years ago
last modified: 9 years ago
Hmm, the more I think about it, the more I think that maybe the 79% transparent (10mm twinwall) polycarbonate, with regular crossbraces, might be the best option... I could use the 1200mm sheet:http://www.polygal-northamerica.com/images/technical/windload_performance_PC10mm.gif

... with crossbraces every 1200mm and it'd have the strength of the 62% transparent stuff, and I could reduce the number of primary arches due to the wider sheet width... hmm, maybe something like that might make a reasonable solution... assuming the durability is decent (I think they warranty it for 10 years, though). It'd have 10% worse transparency than single pane glass but much better insulation and all of the other advantages.

Of course, that's just one manufacturer, I should also look around at others...
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karin_mt
9 years ago
Cool ideas! Where in Iceland? I love that place. As I recall, geothermal greenhouses are somewhat common there? What seems to be they style that is favored there?

I agree that low light is going to be a challenge for you. Might you supplement with artificial lighting? What will you be growing?

I'd go with twinwall polycarbonate, which seems to be a good balance between insulation and light transmission. If you are interested in kits, we have a Riga and it's bomber strong and solid. We have not had winds like you describe (thankfully) but we have had some scary storms and the Riga doesn't miss a beat.

As for building it yourself vs getting help, I'd vote for getting help. You have enough complicating factors as it is, and while there is pride in a DIY project, I would not compromise on materials, or design, or function just to make it DIY. When all is said and done you really want it to work!
Karen Pease
Original Author
9 years ago
Hvalfjörður, not far from Reykjavík :) Specifically, this ravine right here:http://ja.is/kort/?x=366056&y=425108&z=10&type=aerial

Indeed, I already own extensive artificial lighting. About 20-25 square meters of my apartment is a giant grow tent (over 4 meters tall - high ceilings here). The plants never see natural sunlight as it is! A greenhouse will in the long run actually save me a ton of money on power bills. I have dozens of species - banana, dragonfruit, coconut palm, date palm, acerola, coffee, cocoa, several annona species, guava, papayuela, miracle fruit, lemon, pineapple.... yeah, the list just keeps going. :) But even in a grow tent the size that I have now, it's obviously just not enough space. What I love about the ravine idea is how I can just keep expanding it further down the ravine whenever the plants get too big, with practically no bounds.

Greenhouses here are usually pretty conservative / traditional, there's not much innovation in them. They're generally single pane glass, built on flat ground, vertical walls with a v-pitched roof, etc. Sometimes hoophouses are used but not usually year round. Lighting is almost universally high pressure sodium (I use LED at home). Driving through greenhouse towns like Hveragerði in the winter is kinda neat, there's such a bright glow from all of the greenhouses. But yeah, it's all pretty old-school. The only main difference between older greenhouses and newer ones is what they're made out of; old ones are usually of wood or steel, while the new ones are all aluminum.

In terms of getting help, what do you envision? I was thinking about having a licensed engineer go over the design and determine what sort of reinforcement would be required to withstand the winds, and having my excavator guy (who has a couple decades of experience in all sorts of parts of the construction industry) supervise and advise the project. Do you think that would be enough, or are you picturing that I should hire a company that specializes in greenhouse construction to do everything? Beyond the personal-project issue, I just have concerns that they'll add in a ton of labor costs and a bunch of profit taking and the final bill will be something like 3 times higher than the materials costs. And probably won't want to do an unconventional design like mine, or would want to charge a big premium.
karin_mt
9 years ago
Super interesting Karen, thanks for the reply.

I don't know much about greenhouse design so I really can't offer much help. But clearly you're putting a lot of thought into it and research always pays off. Have you checked out some books about greenhouse design?

As for getting help, it really depends on exactly who you'd have available. A level-headed, creative custom builder would be a good partner. I imagine someone that you could bounce ideas off of who could tell you what's doable and suggest practical ways of realizing your vision. I agree that a do-it-all firm doesn't sound like a good fit for you.

It's been quite a few years since I've been to Iceland, but I am heading back there in May. I have such a fondness for that country!
Karen Pease
Original Author
9 years ago
I think that's the approach I'll take then - engineer plus someone with construction experience to bounce questions off of and supervise the project.

Hey, definitely let me know if you have any questions or need any help with anything for your next trip :)
karin_mt
9 years ago
Will do, thanks! Good luck with your project, keep us posted!

Landscape-integrated greenhouse - so many possibilities!

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Landscape-integrated greenhouse - so many possibilities!

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Karen PeaseOriginal Author

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