Historically found on every single continent (except Antarctica), there’s nothing new about rammed earth building. Its use has been dated back to at least 5000BC along China’s Yellow River and outstanding 19th century examples can be found throughout North America and Europe.
It was popular with farmers during the depression after the U.S. Department of Agriculture issued instructions on how to build using rammed earth, but its popularity declined following World War II when the cost of modern building materials significantly dropped. In an age where more sustainable and natural building methods are making a comeback, so too is this simple building technique using raw earth materials.
What is Rammed Earth?
Rammed earth is basically a damp mixture of earth, including sand, gravel and clay, sometimes with an added stabilizer. It’s important that the clay content is not to high, however, which can cause the structure to shrink and crack. In the past, animal blood and lime were traditionally used as stabilizers, while today the latter is still in use, together with materials such as cement or asphalt emulsions.
How do you Build Using Rammed Earth?
While rammed earth can be molded into individual building bricks, more traditionally it is compressed into a mould to create entire walls. A wooden supporting frame is created, before the damp earth mixture is poured into a depth of less than 10 inches, then compacted to around 50% of its original height. The name comes from the labour-intensive process of tamping the mixture down using a long ramming pole, although today pneumatically-powered tampers are more commonly used. The process is then repeated until the entire wall is built. Everything is held together by pipe clamps to ensure it doesn’t bulge or deform, and these can be loosened or tightened as the form is created. In modern rammed earth constructions, the walls are typically built on top of a more conventional foundation such as reinforced concrete slabs.
Then the frames need to be removed immediately, particularly if any surface textures, such as carving or mould impressions are to be applied, considering the walls become too hard to work within roughly an hour. Once the form is dismantled, it can be moved on to the next section and repeated. Windows and doors can also be added by ramming earth around individual forms and it’s important that exposed walls are sealed to prevent any water damage.
Alternatively, rammed earth can be formed into individual building blocks using a machine, then stacked just like regular bricks or blocks and bonded together using a mud slurry, rather than cement.
What are the Advantages of Rammed Earth Construction?
One of the main advantages of rammed earth building is that soil is widely available and a sustainable resource, while at the same time being far more affordable than other building materials. The soil used is typically a subsoil low in clay, meaning that the topsoils can still be kept for agricultural purposes. When using locally available earth, the energy required to build using rammed earth is dramatically reduced when compared to more conventional building methods, together with the costs of transportation. It can be built using largely unskilled labor (as it has been done for centuries before), and the formwork used to build using rammed earth can also be reused again and again.
One of the most favorable properties of rammed earth is that its compression strength actually increases as it cures (something that can take up to two years in some regions). While its strength is less than that of concrete, it’s still strong enough for domestic building purposes and can be reinforced using wood, bamboo or rebar, particularly useful in earthquake and storm-prone regions. Cement can also be added to some clay-poor soil mixtures to increase the overall load-bearing capacity of the building.
Rammed earth also has a high thermal mass, absorbing heat during the day and releasing it at night, reducing the need for air conditioning and heating. It also ‘breathes’ far better than concrete structures, and provided cement renders or artificial sidings aren’t applied, the walls can naturally desorb moisture and avoid any condensation issues. Rammed earth is non-combustible, making it fireproof, as well as being non-toxic and termite-resistant. The thickness of the walls (usually between 12-14 inches) also make rammed earth structures ideal for sound proofing and they can easily be patched using exactly the same material.
Aesthetically, rammed earth structures are also quite pleasing, with a color and texture comparable to that of natural earth. Other elements, such as bottles, tires and timber features are often included to add a creative flair to the structure.
The environmental impact of rammed earth building depends largely on the cement content of the mixture being used and how locally it has been sourced, but it has the potential to be one of the lowest impact building systems available today. From semi-arid regions to the tropics, its design and material composition can be tailored to local climatic conditions. Provided the structure takes into consideration passive solar design, a rammed earth home can use around one-third of the energy of a conventional home and significantly save on energy bills.
What are the Challenges of Building with Rammed Earth?
While the most basic and traditional method of building with rammed earth has a low impact on the environment, more modern and processed variants can contribute significantly to greenhouse gas emissions. In particular, the use of cement in the manufacture of the soil mixture, together with the transport of material to the building site, can significantly increase its environmental impact.
In cool climate areas, the addition of insulation or energy sources can add to the overall costs of building with rammed earth, while in rainy areas, larger roofs need to be installed to protect the earthen walls. Rammed earth building can also be challenging when put up against building officials, bankers and insurers, often taking a more persistent person to secure the necessary means to build.
It’s also an incredibly time-consuming building method when done manually, and in country’s where labor costs are high, this can add significantly to the overall cost of building using rammed earth. California rammed earth architecture, David Easton, is addressing this in a new technique he calls PISE (pneumatically impacted stabilized earth), which uses a pressure hose to spray the earthen mixture against a one-sided form, reducing the time involved in building, while still creating the same beneficial thick walls.
He’s also been involved in creating a rammed earth masonry unit known as the Watershed Block, which reduces the cement content (and environmental knock-on effects) while still creating a durable and sustainable block. So while rammed earth housing has the potential to be an ecological building material, reducing the detrimental effects of more conventional building materials, it depends largely on the individual’s approach to sustainability in their choice of soil mixture and where they are sourcing it.
While rammed earth housing is largely supported by those looking for a greener building alternative in the developed world, it’s across the developing world where it may have the biggest impact. As many cities and towns see a huge influx of people from rural areas in search of a better life, the demand on urban housing has dramatically increased. The lack of low-cost materials and the associated costs of conventional building make secure housing out of the reach of many. Rammed earth housing using locally-sourced earth has the potential to provide an environmentally sustainable and affordable solution.