Strawbale for a jungle greenhouse in a cold climate?

I'd like to be able to grow some tropical trees in south-central canada. In a greenhouse.  I've seen it done with styrafoam, but I want to do that in a natural building context.

I want to build a greenhouse to do that and use strawbale around timber structure for it straw's insulation properties.

I am concerned about high humidity (a result of warm temperatures and frequent top-watering on wet soil in sun) and its effects on a strawbale wall system.

As it's canada and cold/dry...a significant amount of condensation on the windows is to be expected, even if they are doubled.

I could do a lot of drip-sill installation under each window to ensure condensation coming off it doesn't go onto the walls below, but is that even approaching enough? There will be plenty of moisture in the air, and watering, wet leaves, and air flow is sure to throw additional liquid onto the walls as well.

I am concerned that a high humidity greenhouse with lots of condensation seems like it might be a poor fit for strawbale, and I should look for less water-sensitive wall compositions. Is that right?

I'd like to stick within natural building but I'm not sure i have the years required or the team of people I would need to build a cob wall of sufficient thickness for a greenhouse. I'm not sure what other natural building approaches I can take that combine insulation with water resistance.

Tropics is the place that any organic material quickly deteriorates due to high humidity and temperature, so I would recommend avoiding it in direct contact with greenhouse atmosphere.
Insulative, inorganic and natural would be: perlite, expanded clay, some light volcanic stones. If you got access to those materials in bulk you could build 3 wythe wall: cob, perlite + clay slip, cob, or make blocks from perlite and cement. Volcanic stones are rather out of equation, because they would have to be imported.
If you are not against cement you could use concrete blocks, perlite + clay slip, concrete blocks.
You could also make aerated concrete blocks and use them directly for structure or on the outside of concrete block or brick wall.
Cob, light clay, cob probably would also work, especially if light clay had lime additive.
You could also purchase ICF Nexcem (Faswall in US). Blocks are rather expensive (around 3-4 times the price of equivalent size concrete block) but would save a lot of labor. They do not contain any plastics are breathable and I consider them the best ICF system.

I think your concerns are valid. Those bales would have to be sealed impeccably well from the interior to keep from sucking up water and rotting.

Hey Daniel, I agree that your concerns are valid.

I wonder: could you design a system where the straw bales are *designed* to begin decaying, with the intent of changing them out every year or two? Could they be insulating and composting (producing heat) at the same time?

One of the big challenges in the Great White North is that we are shut down for many long months of winter. If you can beat this problem, you could be ahead of the game.

When I tried compost inside my greenhouse it gave off funny odors and didn't really do much for heating. So I wouldn't focus on that benefit, but designing it to be consumed/replaced every year or two could be interesting.

A composting bale wall actually does sound interesting i could build an outside wall of something like rammed earth or compressed earth blocks, put the windows in that, and then line the inside of it with sacrificial strawbales. Those would both be intended to compost and function as insulation until they were too far gone, then spread outside and replaced.

Could be done.

However having a wall you dont have to replace every 2 years seems nice. Id like to opt for less maintenance any time i realistically can.

Perhaps a wall filled with foam glass could do. I was assuming it would need to be unreasonably thick, but I might rerun the numbers.

I've been trying to figure out the best greenhouse for us as well. ( also Southern Ontario)

One thing I had been considering  was to go with a passive solar type. South facing is all windows but insulated walls on the sides and north. I was thinking of a partial roof, to reduce overheating in the high summer, and giving it big overhangs. Then pack straw bales around on the north and sides. They should really up the insulation but won't be inside the envelope and would be converted to mulch every few years. ( where we plan to locate the greenhouse also means they would be super easy to get placed too)

I need to do more research.

Dian Green wrote:I've been trying to figure out the best greenhouse for us as well. ( also Southern Ontario)

One thing I had been considering  was to go with a passive solar type. South facing is all windows but insulated walls on the sides and north. I was thinking of a partial roof, to reduce overheating in the high summer, and giving it big overhangs. Then pack straw bales around on the north and sides. They should really up the insulation but won't be inside the envelope and would be converted to mulch every few years. ( where we plan to locate the greenhouse also means they would be super easy to get placed too)

I need to do more research.

That is exactly the design I had in mind as well. It sounds like people are saying that the moisture in a tropical greenhouse is not a good idea...

The idea with composting strawbales on the outside of solid construction is interesting, but: when they get wet they will lose insulative value, so they would really had to be replaced before they start decomposing. It would not happen if  roof overhang was very large. For a  building of 20x20'x10' it would use around 180 strawbales on 3 sides. Assuming price of $10 a piece it would be quite pricey. If the bales are free then yes.

I did some googling and found this;
'Key Tips for Success
Use Straw, Not Hay: Always use straw (the dry stalks of grain) rather than hay. Hay contains seed heads and is more prone to moisture absorption, which can lead to mold and rot.
Manage Moisture: Wet straw breaks down quickly and loses its insulating properties.
Ensure your bales are kept dry by wrapping them in plastic tarps or treating the exterior with a natural plaster or stucco.
Leverage the "Compost" Heat: If you water and fertilize straw bales inside the greenhouse, they will naturally decompose and generate a slow-release heat.
This process creates a warm microclimate perfect for giving seeds a head start in early spring.'

If you can design the building so the straw is not in contact with the moisture it may last longer. IE a waterproof barrier, metal sheet, ceramic tiles
it may work.

Daniel Andy wrote:I'd like to be able to grow some tropical trees in south-central canada. In a greenhouse.  I've seen it done with styrafoam, but I want to do that in a natural building context.

I want to build a greenhouse to do that and use strawbale around timber structure for it straw's insulation properties.

I am concerned about high humidity (a result of warm temperatures and frequent top-watering on wet soil in sun) and its effects on a strawbale wall system.

As it's canada and cold/dry...a significant amount of condensation on the windows is to be expected, even if they are doubled.

I could do a lot of drip-sill installation under each window to ensure condensation coming off it doesn't go onto the walls below, but is that even approaching enough? There will be plenty of moisture in the air, and watering, wet leaves, and air flow is sure to throw additional liquid onto the walls as well.

I am concerned that a high humidity greenhouse with lots of condensation seems like it might be a poor fit for strawbale, and I should look for less water-sensitive wall compositions. Is that right?

I'd like to stick within natural building but I'm not sure i have the years required or the team of people I would need to build a cob wall of sufficient thickness for a greenhouse. I'm not sure what other natural building approaches I can take that combine insulation with water resistance.

Actually, I do think your worried. A damp greenhouse situation is really hard on strawbale in the long term unless the moisture details are extremely well thought out.
It may be to your benefit to use a more moisture resistant building material for the greenhouse itself and use strawbale for adjacent, dry building elements.

The outside-bale idea is interesting but the wet/rot problem is real. One thing that might help is a wide roof overhang on the north and sides so the bales stay dry. If they're never getting rained on directly they'll last a lot longer. Still probably a 3-5 year replacement cycle rather than permanent, but might be worth it if bales are cheap locally.

Back to the OP, please
1. Is this your first greenhouse build?
2. If so, could I suggest starting with a modest greenhouse to grow peppers, tomatoes, chard ......and observe your results over a full year?
    When you're sure about that success, perhaps try tropical trees the following winter?   This might be a realistic two phase solution.

I would suggest looking at the strawbale greenhouses  created by Chad Midgley of Utah,
(https://youtu.be/LKWYS9G6_GU?si=Hz5-HmRSDbjUsYRy)
but he uses lots of plastic in his greenhouses.

As an alternative to strawbales,  how about using dirt?
Specifically, consider a  Walipini greenhouse.
The earth walls of a pit greenhouse should readily deal with humidity.
I don't think it will remain warm enough for tropical plants on its own, but if you add compost heat, you will essentially have the equivalent of a pineapple pit:

https://en.wikipedia.org/wiki/Pineapple_pit

I don't love greenhouses that require a lot of digging, but for your purposes a Walipini makes sense.

Hi Daniel
Try the ideas from William, spot on for your situation ฝ
Forgive  me for being repetitive, but I think you will be happier with a smaller walipini for 2026.  If it works for you swimmingly,   maybe expand the following winter, Nature as our teacher