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greenhouses

Mike's passive solar greenhouse design/build

Trace Oswald

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posted 1 year ago

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Any new updates on this Mike?

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Mike Haasl

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posted 1 year ago

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Hmm, not sure. The current status is that I'm considering the main interior space to be a "Georgia" growing space. I haven't measured that area getting below 9F. I currently start seedlings in there and have two peaches, four pawpaws, two grapes, two figs and an olive tree in that area. Lots of peach flowers this year but it got too hot in the early spring and I think that cooked them and I didn't get any fruit. Some grapes and I got a fig last year.

The area that was the compost bin now supports a yoga/sunbathing platform and under there I enclose it in the winter and heat it with a milk house heater. In there I have a Calamodin orange, mandarin, two lemons, a key lime and an Australian finger lime growing.

The greenhouse plastic is due for replacement some year now and I'm debating upgrading it with Solex or something like that. If I do that, I'd consider putting some glass near the yoga platform for better tanning. I'd also redo the lower vents since I only need one vent, not a full width row of vents (and thus air leaks).

I'm taking applications for "greenhouse fairy". If anyone wants to play in the greenhouse, grow lots of stuff and make it pretty, it's available :)

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Kirsten DeVries

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posted 1 year ago

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Hi, Mike! We were just reading this thread and are wondering how your greenhouse turned out. We are thinking of doing something similar and we especially like the idea of heating with compost. We are in Michigan, zone 5b. Thank you!

Mike Haasl

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I'd say that in zone 5b it would do much better, especially if you get a bit more sun than me in December. My minimum temp measured so far is +9F and I'm in zone 4a.

The compost didn't work for me and I don't know how to do it inside a greenhouse and not make it smelly/funky/moldy/questionable for human lungs.

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Mike Haasl

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As an additional update, it's probably time to change out the plastic film on my greenhouse. I'm considering different materials, perhaps fancy ones like polycarbonate or Solexx. Solexx seems interesting but it seems like it's on backorder for about a year. I'll look at polycarbonate next. My rafter spacing is 4' on center and the pieces would ideally be around 18' long if memory serves...

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Ebo David

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I've heard from several people about using different coverings (greenhouse plastic, multicell acrylic, etc.). One guy (I forget which video he produced) designed a greenhouse for the fancy multicell acrylic, and ended up putting on some regular greenhouse plastic just to get going. It worked well, and then he did a cost benefit analysis and found that the nice stuff cost 30x to 50x, and was only expected to last 10x as long. Most people I know just use a good quality UV resistant heavy greenhouse plastic, and it lasts them for years at a time.

Hope this helps.

EBo --
Master Gardener (Prince George's County, MD, USA)

Mike Haasl

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Thanks Ebo, I was surprised that Solexx only had a 10 year warrantee compared to 4 for plastic film.

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thomas rubino

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Hi Mike;
We have had solexx on our greenhouse for apx 13 years now.
It shows its age but is still doing its job.
We bought the rolled solexx, 4'1.5" wide, 100' roll shipped free.
The hard panels were scary truck freight shipping and had to be ordered.

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Ebo David

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I have not looked closely at Solexx, and it might well be worth the extra cost. I just remember pricing the double wall ridged panels for a 48' greenhouse at something like $14,000, and a high quality greenhouse plastic that could be expected to last 4 to 6 years was $300 or so. The ROI between the two products were a no-brainer, although you do have to account for the downtime while you are replacing the covering...

BTW, remember that the *warranty* is typically 1/2 to 3/4 of the life expectancy of a product. The manufacturers do NOT want to have to pay for anything once the job is done, but the warranty will help them get jobs. So there is a fine marketing line where it is cost-effective to set the warranty duration. So, when looking at the products, you can often expect them to last 2x the length of time, but often in a degraded capacity.

BTW, Gorilla Glass was working on a greenhouse glass product several years ago. I bet is it uber expensive, but likely have a life expectancy of 100 years...

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Master Gardener (Prince George's County, MD, USA)

John Weiland

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thomas rubino wrote:Hi Mike;
We have had solexx on our greenhouse for apx 13 years now.
It shows its age but is still doing its job.
We bought the rolled solexx, 4'1.5" wide, 100' roll shipped free.
The hard panels were scary truck freight shipping and had to be ordered.

I could also see where property location latitude might impact this as well. All of our implementation of passive solar has been vertical....no angled glazing for summer sun (northern hemisphere). I suspect this may extend the life slightly due to the fact that the panel (5/8" twin-wall in our case) cells are supporting much of the panel weight plus they are not getting direct summer sunlight and daylength. And our panels were obtained used.....quite probably 8-10 years old at the time of acquisition and sporting several patched holes from hail damage. So along with Thomas R. observations, with some care they may last quite a bit longer than the warrantee indicates even if the quantity and quality of light transmission suffers a bit with that aging. Great to see all of the valuable info and experience detailed here for northern homestead greenhouse builds!

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Ebo David

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Gack... I somehow clicked on the link to no longer receive updates from these posts. Sigh... Not sure I will remember to check this otherwise...

EBo --
Master Gardener (Prince George's County, MD, USA)

Jack Sato

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Location: New Hampshire Zone 6A

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posted 4 months ago

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Hey Mike!

Hows things going? This has been an awesome thread to read through! hows everything looking? your greenhouse looks awesome and the yoga area sounds fantastic! Did you end up putting some glass in there as well?

I hope all is well! Thanks for the inspiration!

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Mike Haasl

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posted 4 months ago

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Thanks Jack! I haven't had time to improve it this year or last. But the plastic has started to fail so I do need to reskin it this summer. I have been leaning towards twin wall polycarbonate but I'm not sure if I need to add any structure to hold it up. My rafters happen to be on 4 foot centers but it might need some horizontal support. Which is doable if needed.

I think I'll skip the glass for the yoga area. Getting glass up there would be a real struggle and a potential safety and air sealing nightmare.

Based on my experience, I'll be able to go with one or two tiny vents at the bottom, instead of the row of patio doors. And I'll remove the reflectix roller and associated hardware at the ridge.

Fun project, anyone wanna come help with it? :)

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Phillip Gapp

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Location: MN, USA

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Hi Mike! I'm Phil and I recently became interested in permaculture, earth structures, passive solar, etc.! Found this thread and (being in the Twin Cities, and your recent posts inviting help) just have to write

Many of the inspirations for your design have been floating through my head, and I'm beginning very small scale experiments with everything from earth tubes and buried cisterns to walipini excavation and insulation. Some years future I'd absolutely love to build something like your greenhouse.

I read the first couple pages of the thread and the last, but haven't caught up entirely. What are your current goals besides replacing the 'glazing'? What do you need help with? What would you like to see planted? How long would you be comfortable having a guest

?

Seriously though I'd love to visit, and if it makes sense for us, discuss volunteer goals and plans. Even with experiments and daydreaming I still have spare time and idle hands.

Thank you!

Life before death. Strength before weakness. Journey before destination. - Brandon Sanderson

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Mike Haasl

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Hi Phil, thanks for writing!

My official current goal is to replace the glazing. It's bought and ready to go anytime before it gets cold out. Along with the glazing, the upper vents need to be worked on so they open farther and lower vents would need to be made. I have some nice side quests that I could add as well:

One would a system to collect heat from the main greenhouse during the day and store it in the mini-greenhouse to keep the citrus alive. I have the stuff for it but haven't gotten around to doing it.

Another would be to make an actual door from the seasonal mini greenhouse out into the main greenhouse.

Lastly, the exterior cement board is starting to flake off so I'd like to cover that with something more durable, perhaps like metal roofing

Planting wise, I'd love to see the whole thing be a gorgeous oasis of flowers and food. Currently it's growing some trees and seedlings in the spring. I have 4-5 citrus in there that are fruiting, 4 pawpaws that are 3 years old, grapes, figs and peaches. Haven't gotten fruit off the figs or peaches yet but there are little fruits on the peaches so maybe this year. I guess an irrigation system could also be a side quest...

I'll PM you about the visit idea, I'm wide open to it. Thanks!

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Kevin Hotton

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posted 2 weeks ago

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Hi Mike,
Very nice greenhouse you built. I am new to Permies and have enjoyed reading your saga. I live in Pagosa Springs, Colorado, so cold but much sunnier in the winter months. Pagosa Springs is the home of Growing Spaces geodesic dome greenhouses. I am a retired Mechanical engineer with extensive thermal-science experience. What you were attempting to do was very difficult. Cloudy weather in winter just kills the solar energy that you need to have any chance at keeping the greenhouse interior above freezing. You did the best you could with the climate and budget you had to work with. Thanks for sharing. Kevin

Mike Haasl

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Thanks Kevin! I think the bubble wrap "Reflectix" between the poly layers has some real potential if it can be extended and retracted uneventfully. I suspect if that worked and was programmed well, and the vent doors at the bottom were fewer in number and sealed better, it would at least stay above 20F in my zone 4b climate. And I think "tropical" would be possible down south by Chicago... Or in somewhere sunnier like WY

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Ebo David

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@Mike, what does your foundation look like? Is it on cinder blocks? Is the exterior perimeter insulated?

There is an interesting article in a Nature publication on:

Dong, J., Tong, X., Xu, J. et al. "Diverse greenhouse farming systems underpin high land‑use efficiency and food security in China." Commun Earth Environ (2026). https://doi.org/10.1038/s43247-026-03711-9

Turns out that in Northern China, they build their greenhouses with thick thermal mass walls, and sometimes wrap the exterior foundation (and north walls) with some insulating material, and they typically keep above freezing without an HVAC. It turns out that if you insulate around the foundation wall, it adds a lot of the dirt to the thermal mass of the greenhouse, and the cold does not seep in from the top few inches of the soil. Digging around the foundation to add insulation can be a daunting task, but there are people who have buried it at an angle instead of just straight down. It has been years since I have seen the model output of the thermal profiles (vertical vs slopped orientation). Digging a 6" deep trench 4' wide is easier than a 4' deep trench 6" wide.

Hope that helps.

EBo --
Master Gardener (Prince George's County, MD, USA)

Mike Haasl

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posted 2 weeks ago

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It's a "shallow frost protected footing" if I have the words right. Cinder blocks a foot or two high, sitting on around a 8" by 24" shallow footing with the bottom around 2' deep relative to grade. Then R20 closed cell styrofoam outside of that vertically for 2' and then sloping away for another 2' to give 4' of frost protection. Which is what I think you're suggesting so... Yay!

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Ebo David

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Yep. That is one way to do it for sure

How is your foundation holding up with only 1 to 2 feet deep (which is 1/4 to 1/2 standard building code), and in zone 4a? Just curious. I do know that in some places (like Norway) they have a building system where the entire house is built on an thickly insulated encased slab, and it works for them...

EBo --
Master Gardener (Prince George's County, MD, USA)

Mike Haasl

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To the best of my observation, it's doing just fine. The shallow frost protected foundation design keeps the frost from getting under the foundation so it can be shallow. It's also very sandy and well draining here. In my area, with snow on the ground, the ground rarely freezes more than a few inches deep. Except where snow's been removed or packed down. The ground on the inside of the greenhouse doesn't freeze so the warmth of the earth is rising up and helping heat the greenhouse a little bit.

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Ebo David

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Do you have a temperature logger inside the greenhouse? If so, I can plot the effectiveness of the insulation. To do a proper job for a paper/report, I would try to find a greenhouse where they did not have any insulation outside, and ideally, set up soil temp probes inside, outside where it snows, and outside where it snowed but you kept it clear. That would give you an idea of the contribution of snow-depth and insulation.

EBo --
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Mike Haasl

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I don't currently have a temp logger. Probably makes sense to do some tracking... I have a techy buddy who's helping on some projects and might geek out on making that happen. My greenhouse is fairly different from others (insulation wise) so I doubt much could be drawn from a comparison

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