I agree with the above.
But for my personal
experience, our school has several different buildings that are passive
solar heated and made of earth. Off the top of my head, here are some pros and cons that come to mind.
Adobe bricks <-> old-style Himalayan rammed earth (like formed
cob) <-> modern rammed earth (denser) <-> big straw-clay bricks <-> cob <-> stone masonry
Trombe walls <-> seasonal attached greenhouses <_> direct gain south facing sunrooms
Adobe bricks:
- Available for sale here, so from idea to finished construction can be very fast.
- If you're making them yourself, they dry faster than monolithic rammed earth or cob walls, due to more surface area.
- But you have to mix, make them, turn them, dry them, transport them, and then build, as compared to rammed earth or cob, which you only mix and form.
- Structurally and thermally can be less wonderful than rammed earth for various reasons, unless done very meticulously (which is not the case here).
- The mix seems to need more clay than some of the others, in my experience.
Old Himalayan rammed earth:
- My favorite. I just had my new house built with this.
- The mix is a little wetter than modern rammed earth, so once it dries it's more porous and insulative.
- Less densely packed than modern rammed earth, so may require less material, but then again we made the walls very thick at our school. Which is wonderful for every possible reason, but uses a lot of material.
- Takes longer to dry. I complained about my house taking two seasons (ie years) to build) until my friend finished hers and moved in in a single season, and then had a big moisture problem all winter.
- Seems very forgiving of a variety of materials. At our school we misidentified some fine silt as clay, and built the whole huge two-story building out of a mix that had this fine silt as the binder. Turns out to work fine, the walls are very strong still 22 years later, and when we need to bust a hole through, it's extremely tough and strong.
Modern rammed earth:
- Mix is considerably sandier than wetter methods like adobe, old rammed earth, and cob.
- Needs to be packed very densely, possible by hand but better with a pneumatic tool.
- In ideal conditions, with perfect planning, and good experience, it can be so smooth and attractive as not to require plastering, which avoids an additional step. I'm not fond of this though, because the conditions and planning are never ideal, and without plaster it's harder to put up with chips and bang-ups.
- Less insulative, but more thermal mass, so at a recent building in our school we used it only for the internal wall.
- Moderates temperature best of anything, having both thermal mass and insulative qualities, and giving its stored heat in a slow comfortable way. Moderates humidity, which turns out to matter more than you thought, and is really nice, which is true of any earthen building. Moderates sound too.
- Supposedly has even better structural qualities, so can be built thinner than some of the other methods. Good for saving space, which isn't our issue at the school or my new house, but could be an issue in a denser or urban environment. But also combines with less insulative to make it less suitable for external walls in an extreme climate. I saw several of these used in Australia but their climates were rather temperate.
Straw-clay blocks:
- We like to think we came up with this ourselves. It's a mix of a good
local sticky clay (true clay) and
straw. We use it as insulating external north, east and west walls.
- Probably not great compressive strength but we're using for one story walls anyway (load bearing).
- The block shape means it dries faster than monolithic walls.
- Straw works well and makes a good block whereas wood shavings are not very good at all. But here, straw is not a waste product and we have to buy it, whereas wood shavings are pretty much the only biomass waste product that can be gotten for free in the whole region.
- If we can get it together to make the blocks ahead of time, construction is very fast, maybe faster than adobes because they are bigger but still liftable by one person.
Straw bales:
- We haven't used this because bales are not made here, but I have some opinions anyway.
- Very thick walls, so take up a large area which is a problem in some places, eg not good for urban areas.
-
Mice can get in and make large runs inside, usually near the bottom, which is structurally bad.
Cob:
- Fun for a small project by people with time to spend. Our students have made some fun structures.
- Not as easy or fast as you thought it would be.
- Lovely, charming, flexible, shapeable.
- Probably shares all the wonderful qualities of old-style Himalayan rammed earth that I love: moderates temperature beautifully, as well as humidity and sound.
Those are the ones I know much about. I live in a dry climate with very cold winters and warm summers, so thermal mass and earthen walls are great here. Other climates may require different materials or offer different materials.
Oops, I didn't even get into the passive
solar methods, and my battery is dying. But my favorite is the attached seasonal
greenhouse. I've written about that elsewhere on Permies.
