Cristobal Cristo

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.

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.

My soil mixture was still cloudy after a week. Of course I could estimate the clay contents at this time, but was not in hurry and after 3 weeks the water got cleared. Possibly my clay has finer particles that keep cloudiness longer.

Josh Warfield wrote:For sure, this would be true if there were no such thing as building codes.

Building codes are recent and people were building foundations for millennia because they make buildings last and most humans are too poor to make disposable things.

Josh Warfield wrote:But I have not so far seen any winter damage on the small foundations I've built, and the sketch from OP is not much larger than those. My theory is that a 6x8 foot rectangle of 10 inch thick cob is sufficiently strong as a unit, that it's not likely to crack no matter how much the dirt might shift underneath it.

It's quite possible and I have no reason to not believe you, but I also know how roads and streets look in Midwest cities after the winter. It's a tough and destructive environment. Personally - I would not dare to build unstabillized clay building in such climate and if I did, it would have oversized foundation and large overhangs.

For such test I was using 3 times more water than soil. Shaking for 10 minutes and left for 3 weeks.

Josh,

Bond beams are used in all masonry constructions and not only in seismic zones. It just helps holding walls together, helps resist forces transferred from the roof or wind, equalizes stress distribution in uneven walls. Old adobe, stone or brick buildings had bond beams made of heavy timber. Ancient Greeks were connecting architrave slabs with cast in place lead anchors.
There are many buildings in not seismic zones that have walls cracking, because the foundation shift/heavy roofs and lack of bond beams. Bond beams help thinner walls in greater extent than in thicker. Some old adobe buildings survived earthquakes because their walls were very thick (and braced with perpendicular walls or buttresses).

Of course any building can be built with no foundation, but if such things lasted, people would be glad to eliminate it long time ago, because foundations are costly, but the reality is different.

Flimsy 2x4  actually will be much less demanding for foundation, because it's light and flexible. Mobile homes can be supported by several concrete blocks. A 2000 sq ft stick building structure will weigh around 15 tons. The same size adobe building with 16" walls will be 200 tons just for the walls. It has to be supported by something, because it will sink unevenly and it will crack, especially in loose//not compacted/clay soils.
Locating foundation below the frost line is especially important in sandy soils which will be easily penetrated by moisture and freeze. If foundation was located on solid rock it would be more forgiving to frost line requirement. Also slab foundations are more resistant to freezing problems, especially if insulated. All of it could be determined by geotechnical analysis, but since we are talking about simple, cost efficient building it's better to copy proven solutions.

If the structure is experimental then it can be built any way but if someone agreed that Aud will build some cob structure on her property - the best approach should be taken, not only from ethical standpoint but also to not give alternative building methods a bad reputation. Also wonderful dryness of Colorado is less wearing on buildings than harsh Wisconsin winter and humid summer which is not a traditional place for cob structures. People in such climates traditionally built from wood logs (in later times also from fired bricks).

Alix,

I'm sorry for delayed reply.
The leaf shape does not resemble anything I grow: seven different muscats and few wine varietals.
The leaves resemble Vitis californica and also my St George rootstock, so it's telling me that there is a chance that your grape may be something that got "reverted' to its ancestral gene pool - either a rootstock that took over the scion or a seedling. Most grape rootstock will not produce anything edible. Grapevine this large should already have some fruits. If it does not produce something within a year I would consider chopping it and grafting with a known varietal - easier say than do as I'm 100% unsuccessful in field grafting in my climate.

Traditionally for adobe it's assumed for the height to not exceed 10 widths of the wall, because the material is rather weak. Multilevel adobe does exist in Sanaa, but in most cases it's used for single floor construction. If I needed to build higher than one level I would use fired bricks/stones and either heavy timber ceiling/floor or vaulted ceiling/floor (which would require sufficient wall thickness, buttresses or bond beams to resist vault's spreading forces).
SIRE rammed earth allows for quite tall buildings. This one is 51 feet (15 m) tall:
https://sirewall.com/project/brinton-museum/
but it uses concrete slabs for floors so they definitely help to stabilize it. I think that SIRE wall could be the future of building materials, but at the same time I do not like it, because it's better fit for modernistic architecture and it would difficult to add architectural details within rammed wall that can be easily created with block by block (and brick by brick) construction.

For fire resistance adobe or solid fired brick walls (exterior and interior) would be the best. For stones - variation of their crystalline structures could make them behave in less consistent manner. Concrete, concrete blocks or lime block would be less resistant, because cement/lime starts decomposing around 400 C.

Masonry vaulted ceilings would be the best protection, followed by heavy timber roof structure. For timber - hardwood would be more difficult to ignite than softwood.
If timber is used for the roof, it's crucial to protect it by continuous masonry cornice traditionally built in the past from stone and in second half of the millennium from bricks. Not only it protects, but it makes the house looks next level better - by creating geometric border between the walls and the roof surfaces.

The roofing material of choice would be ceramic, followed by stone, concrete tiles and then metal. In case of masonry roof structure it would not matter much, but for timber one, the ceramic/stone tiles would be the best, especially if laid on clay mortar that would provide a lot of mass to absorb heat.

The next defense would be external metal shutters which protect the interior of the house from quickly heating by the sun (in fire prone areas usually extremely intense) but also protect the windows/interior from flying embers and heat radiation (if neighboring house is on fire). They would help immensely and are in regular use in southern Europe, but in US they were reduced to some plastic, non-functional, "decorative" gimmick. Very sad.

Painting the house white also helps to lower house overheating, but would also make it more resistant to infrared ignition. I'm astonished to not see more houses painted white in the sunny West//Southwest.

I call it "passive" fire proof design that will work without any maintenance, electronics, water, etc.

Of course no vegetation close to the house, would be the first and easiest area of improvement.

Wood/plastic will always burn, because it's flammable. Wood will also attract pests and they will always find the way, because they are small, patient and come in thousands. Any cavity in framed building will be inhabited sooner or later.
Solid masonry solves these problems.

If you are in cold Wisconsin, please make deep footings. If the soil has high clay contents, make them wide enough. Such building will last.

For round building I would definitely build a dome. I consider a good wood roof structure to be more complicated than all masonry walls and foundation. Masonry is just easier. Looking for a heavy timber carpenter stalled my construction for months.
You could also make blocks with higher straw contents to make them lighter for the dome. They would be also insulating to some extent. For my barn/coop I have built barrel vault from bricks then covered with perlite concrete  (also excellent insulator) to form gable roof and then laid rooftiles with clay mortar directly on perlite concrete.
You could also make aerated concrete blocks

If you go the masonry dome route, please pour properly reinforced concrete beam, so the (relatively thin) walls will not break apart under the dome load.
Please note that for dome roof it will be more difficult to create eaves protruding enough to protect your cob walls from the harsh Midwest weather. I think this may be one of the reasons why round structures got somewhat popular only in arid regions.

Have you considered square structure?