Natural building is not as straightforward as the name implies. The term natural in this instance refers to the main building material, not all the materials. Recycled content like glass bottles and tires are commonly used by natural builders. Cement is also a common addition to several natural building materials.
Earth is the primary building material for about one-quarter of the world’s population, mostly in the developing world. Natural building is popular in the developing world because it can be done manually. In the West, however, natural building is slow to catch on because it’s typically rather labour intensive. And when comparing building costs dollar for dollar the cheaper method almost always wins out. Mechanization has been creeping into natural building techniques as a way to cut down on the high costs of labour. Natural builders have many techniques to choose from, whether they want a highly sustainable option, a quick and easy method, one that’s labour intensive or one that’s not.
The term cob denotes the mixture of clay, sand, water and straw (or other fibrous material) that’s mixed together to form palm-sized loaves. The most common way to mix cob is manually (through a process of mushing it together by foot and flopping it around like a pancake on a tarp), but it can, however, be mixed by machine. Cob walls get built up from the foundation until they form a monolithic structure, meaning it’s one solid piece, as opposed to compressed earth block buildings, which are made up of many small blocks stacked on top of one another.
Adobe construction has been practiced as far back as 6000 B.C. Three of the same basic materials are used as with cob (clay, sand and water) except the fourth fibrous material is only used sometimes. Once mixed, the adobe mixture is left to dry in forms until they become hardened bricks, which are then laid by masons. In locations where a building will be subject to harsh, wet weather, adobe is sometimes stabilized with a bit of cement or asphalt emulsion to keep it held together.
Compressed earth blocks
CEB is a mechanized alternative to adobe, which cuts labour costs significantly. Unlike handmade adobe these blocks are compressed by machine and produced with precision, yielding blocks that are uniform in size and shape, which require no mortar as a levelling compound (they can be dry stacked).
Earth is the main ingredient here as well, but instead of stacking or laying the material, it is tamped or compressed into place, usually with the use of forms. Today, mechanized equipment is generally used to do the compression.
Straw is a highly insulative renewable resource, making it a fine natural building material. The drawback is that straw must be kept dry or else it will grow mildew and rot away. Strawbale building can be either non-load bearing, where a post-and-beam framework will support the structure and straw is used as infill or load-bearing. Non-load bearing is the most commonly employed method of strawbale construction.
Cordwood refers to the short pieces of wood one would normally see in a fireplace. But rather than burning them up for fuel this wood is lined up with their ends sticking out and held together by mortar, making for a nice, natural look. Like earth, it has a high thermal mass. And like strawbale, it also has a high insulation property. In this way it makes a great building material. It does require mortar, but it is possible to use cob rather than cement for the mortar.
Like earth, wood is another ancient building material. If wood is harvested from a certified source (i.e. FSC) that regenerates their forests and is sourced locally, it can be a highly sustainable natural building material. In pole construction, wooden poles are dug into the ground (which can rot quickly) whereas timber framing (also known as post and beam construction) uses a separate foundation.
Like earth and wood, people have been building with stones for millennia. And why not? It’s a beautiful, durable material with a high thermal mass. With today’s range of building materials, however, stone masonry is most commonly seen in patios and garden walls.
Paper from any source can be salvaged and turned into papercrete, by blending paper, cement and water together in a big mixer. As with some other natural building materials, the inclusion of cement detracts from its sustainability.
This construction method is similar to concrete in how it’s made, but it’s composition is different. Rather than using sand and gravel it uses typical soil as an aggregate.
Green Home Building: Natural Building Techniques
The Art of Natural Building: Design, Construction, Resources by Joseph F. Kennedy et al.
The Natural Building Companion: A Comprehensive Guide to Integrative Design and Construction by Jacob Deva Racusin and Ace McArleton