Rammed earth, an ancient construction technique, uses soil, sand, and sometimes a little Portland cement, compressed into forms to create thick, solid, and often beautiful structural walls for buildings. One of many traditional (now considered alternative) construction methods, including straw-bale, adobe, cob, among others, rammed earth is typically relegated to owner-built or specialized homes due to the high labor costs. Rammed earth, and other traditional building methods have been pretty much completely replaced by more industrial systems, primarily stick framing, as well as masonry, structural insulated panels (SIPs), and even insulated concrete forms (ICFs). I have no personal experience building rammed earth, but I understand the concepts and appreciate when someone takes on a project using unusual methods, particularly when they do it right. Unfortunately, the only example of rammed earth construction I have seen in person does not fall into this category.
I had the opportunity to visit a very high-end custom home under construction in northern California a few years ago. Key features in the house were large rammed earth walls that served as central elements of the architecture. The walls were two stories tall, made of beautifully striated colored earth, with a subtle curve, and cast-in art niches. Because of seismic issues, the walls were heavily reinforced with steel, all hidden inside the earth with the exception of heavy steel lintels at openings. Rather than serve as the primary walls of the house, these rammed earth “sculptures” were primarily decorative elements to which wood framed sections were attached to provide most of the living space. I don’t have any particular objection to over the top high end homes – I’ve built and renovated plenty of them – but it seems to me that using rammed earth exclusively as a design element approaches silliness.
Rammed earth traditionally used local soils, materials, and labor to construct inexpensive, durable structures where other materials such as wood and masonry were difficult or impossible to find. It doesn’t provide much insulation, but the thickness of the walls does provide some tempering thermal mass, useful in passive solar designs. In cold climates, it usually needs some additional insulation to maintain indoor comfort. Also, even though it only uses a small amount of cement, the fact that the walls are often as much as two feet thick, they can ultimately use more cement than a standard concrete wall.
In the case of this particular home, the walls weren’t serving as thermal mass for any passive solar designs, they weren’t providing much in the way of structure (that was the job of lots of wood and steel), and, because they didn’t care for the color of the local soils, they imported truckloads of dirt from as far away as Nevada, negating the value of using local materials.
If you want to build yourself a low-impact, modest sized home, made of local materials, and you don’t mind working really hard (or paying others to), a rammed earth house may be something to consider. When it is used almost solely as a decorative element in a starter castle, it is more of an architectural conceit than a legitimate building material. Architects and builders should carefully consider how they use traditional materials and use them appropriately rather than for bragging rights.