Exploring Earth-based Construction Methods
When we think of architecture, we often think of huge glass and steel structures or conventional homes with wooden frames. While these are the most common type of structures built today, they are relatively new inventions when compared to the scope of architecture throughout human history. Building technologies involving earth are among the oldest of human technologies but there are still advantages to using them today including longevity, resistance to temperature change, cost, and a lack of skilled labor necessary to construct them.
Rammed earth is about as simple a building material as you can get. The name is pretty much spot on when it comes to describing what it is. It’s basically damp sand, gravel and clay that is put into a wooden form and then repeatedly tamped down until it becomes solid. Historically the mix was stabilized further with the addition of limestone or animal’s blood. More recently builders have used cement or asphalt instead. In rammed earth construction, this damp dirt mix is poured into a mold and compacted down to around half its original height. This is repeated until you reach a desired height and then the walls are left to dry naturally, essentially turning them into a type of man-made sandstone. Rammed earth can also be formed into blocks which are then stacked and mortared together with thin mud. Unreinforced rammed earth has extremely poor resistance to seismic activity, as one might expect, and this has sadly been witnessed during earthquakes in many locations around the globe. However, when it is reinforced with either rebar or wood, rammed earth’s resistance to seismic forces goes way up. It is very similar to concrete in this regard.
A step up the technological ladder would lead us to cob. Cob is similar to rammed earth in that it is a low-cost, natural building material but it differs in that it features an organic component that helps make it more stable. Cob is composed primarily of subsoil which is the layer of soil under the topsoil. The subsoil is made up of sand, clay and silt and is much lower in organic content than topsoil. In cob, the subsoil is does the bulk of the work, the fiber (usually straw) acts as a kind of rebar which gives the cob strength and of course the water makes it workable. Cob was a very common building material throughout Europe and in fact there are many cob structures around today that are inhabited despite being more than 500 years old. Cob only recently came to the USA but thanks to the green building movement, it’s gaining popularity.
Adobe is very similar in composition to cob with a clay rich soil providing the bulk of the mix and an organic component – either straw or animal manure – providing further strength. Where adobe and cob differ is that adobe is typically fashioned into bricks and then built with where cob is more often spread in its wet form over a surface to build up a wall. Adobe buildings are incredibly common in the middle east and in the American southwest, particularly in New Mexico. Adobe has many of the same qualities of other earth-based building methods including huge thermal mass and great durability though it suffers from susceptibility to earthquake damage.
The newest, and maybe most exciting development in the realm of earth-based construction methods came from an Iranian-American architect named Nader Khalili. Khalili is best known for his invention of the Superadobe method of construction. Khalili was inspired by a NASA contest to come up with possible construction methods that could be used on the moon. This contest stipulated that because space and weight were extremely limited on a spacecraft, a means of building structures quickly and easily that would require little space in transit needed to be devised. Khalili’s idea was to use long, tube-shaped woven plastic bags which would be easy to store, and pack them full of lunar soil. These would then be arranged in dome shapes. He called this Superadobe and created several prototype structures as proof of concept. Ultimately, NASA abandoned the idea of lunar construction but seeing the value of his idea as a means of quickly and cheaply constructing shelter, he worked on perfecting it. One of the biggest innovations came in the form of barbed wire. Khalili discovered that by placing a string of barbed wire between the courses of bags, he could drastically increase the stability of the structure and make it much more seismically resistant without the need for large pieces of steel rebar. Eventually, Nader and his children formed the Cal-Earth Institute in the desert town of Hesperia, California and began teaching this construction method to anyone who was interested.
One might picture a house that is made essentially from sandbags to be dark or depressing, but the end result is the exact opposite. The dome and arch shapes that are so prevalent in Superadobe construction draw heavily from traditional Persian architecture and are quite beautiful. Most windows are arch shaped as well and many builders include various skylights and oculi which flood the spaces with light. Because the bags that hold the earth in shape have somewhat limited resistance to UV light, the structures must be protected. This can be done in several ways with the most common being to plaster them. These homes are particularly good in desert climates because their thermal mass and plaster shell resists heating from the desert and maintains a fairly constant temperature. Far from being modern caves, Superadobe structures can be outfitted with all modern conveniences including plumbing and electricity as well as heating, etc. Costs range of course, but based on our research, they cost typically around 2/3 what a conventionally framed home would and has much less of an impact on the environment.
We love the beautiful and sleek modern homes with their glass walls and atriums and we love achingly beautiful Greene and Greene-style craftsman style homes. Many of these types of homes are simply unaffordable for most people, particularly in Southern California where housing prices are climbing ever towards the stratosphere. The environmental concerns brought about by traditional building methods and the heating and cooling inefficiencies of their design are also extremely concerning in a world where resources are becoming more and more scarce. It’s exciting for us to see ancient building methods being employed to great success and even improved upon in the case of Superadobe to make them even more viable in today’s housing market. The aesthetics of these kinds of structures might not be for everyone, but we are really excited to see what people build using them in the coming years.