Questions about Rammed Earth Structures

In an old post of Owen’s about Ancient Rammed Earth Structures, I have been responding to Mirosan, who asked these questions:

“So, so far all three mentioned are in arid if not desert situations. Is that because other structures (of rammed earth) in non desert or non arid climates have succumbed to the elements or just that these are what came to mind?”

Kelly: “Earthen construction started in the Near East in arid lands, so there is more of a tradition there. And yes, wetter climates would tend to shorten the life span of earthen houses, or at least require more maintenance.”

Mirosan: “So, to take that conversation a little deeper, what would you say are the main downfalls of rammed earth technique/structures in non arid/desert situations? Would it be the soil movement based cracking or the earth walls working expanding/drying with the fluctuating humidity levels? Maybe mold? Cracks and water ingress?”

Kelly: “Well, there are plenty of examples of durable rammed earth buildings around the world to attest to their resilience. They are vulnerable to seismic activity for sure, since they are generally not reinforced for such movement. Expansion and shrinkage would depend on the soil mix, and if there is too much clay this can be a problem. Mold should not be a problem unless there is organic matter in the mix. Earthen buildings can generally handle humidity better than practically any other technique, and can be a very healthy way to moderate humidity. Modern rammed earth buildings often add some cement stabilizer which helps with possible erosion, but this is best mitigated by wide roof eaves and proper foundations.”

“Rammed earth walls do not provide much real insulation in climates with extremes in temperatures. One way around this is to sandwich insulation between two rammed earth walls, and this has been done quite successfully.”

Mirosan: “Hmmm, you’ve given me much to think about mainly in the area on insulation. I did think they were insulative by the sheer thickness and poor heat conductance through it. Something like the millions of tiny air pockets in foamcrete… could these not be replicated by including a lot of spheres of styrofoam like material? Air puffed popcorn – it is used in packaging instead of styrofoam. Large insulative sheets in between two layers of rammed earth would tend to weaken a wall mechanically and impair breathability. The insulation could also be placed on the outside surfaces and that would be ideal in arid hot places but not ideal elsewhere. It also does not solve the breathibility issues. Fiberglass batts are breathable but their insulative property degrades once humidity goes up and they are not a natural product at all. It’s a given that well sized eaves are a necessity as you rightly pointed out.”

Kelly: “Adding insulating aggregate to rammed earth could increase the insulation value slightly at the expense of cohesive strength. Modern insulated rammed earth is a well researched science, and you can read more about it at https://sirewall.com/ The walls do remain breathable in both directions. Fiberglass batts would not be a good choice. Rigid insulation can be attached to the outside and then protected with plaster, but this is not a natural solution. Insulating rammed earth as described is beneficial in both hot and cold climates”

Mirosan: “Feels to me that it may be better for me to look into hempcrete or strawbale methods or, of course, aircrete as these provide insulating properties as part of the basic material. Alas the first two are not as bushfire proof as the latter but way more seismic activity tolerant.”

Kelly: “I believe that hempcrete is rather fireproof. Another option might be earthbags filled with crushed volcanic stone (called scoria). This is what I built my house out of. It can be fireproof, earthquake resistant, durable, and quite insulating.”