Rammed earth has been used in construction for thousands of years, with evidence of its use dating as far back as the Neolithic Period. Commonly used especially in China, the technique was applied to both ancient monuments and vernacular architecture, with the Great Wall utilizing the technique. Though interest in rammed earth declined in the 20th century, some continue to advocate its use today, citing its sustainability in comparison to more modern construction methods. Most notably, rammed earth structures use local materials, meaning they have low embodied energy and produce little waste. Below, we describe how to build with this material.
To start, working with rammed earth requires a strong understanding of the climate and location in which the structure is to be built. Typically, the rammed earth technique works best in climates with high humidity and relatively moderate temperatures. In colder climates, rammed earth walls may need additional insulators, while in locations with high rainfall, they need additional protection against rain. Additionally, many countries lack regulations for rammed earth buildings. For these reasons, rammed earth construction may not be feasible for some locations.
Once the location is deemed to be feasible, the framework for the walls may be built. Usually consisting of two parallel plywood panels, the frame is then filled in with a layer of damp earth, which typically includes sand, gravel, clay, and a stabilizer. After this small layer is added, it is compressed into around half its original volume using a pneumatic tamper. This process is repeated iteratively until the frame is filled with compacted earth, allowing the wood to be removed and a free-standing rammed earth wall to remain.
To improve some of the shortcomings of this ancient technique, additional measures can be taken to enhance the walls. For example, to improve rammed earth’s relatively poor thermal performance, architects may add extra insulation to the walls. If applied externally, the insulation should be vapor-permeable to allow evaporation; if applied internally, insulation options are much more flexible, although the insulation should not be attached directly to the face of the wall. To account for possible water damage, rammed earth walls should be sheltered by long overhanging eaves and lifted on solid raised footings at least 225 mm above ground level.
Sometimes, to remedy these shortcomings as well as increasing the load-bearing capacity of rammed earth walls, cement will be added into the original soil mixture as a stabilizer. This concoction is referred to as Stabilized Rammed Earth (SRE) in contrast to Rammed Earth (RE) and is common particularly in Australia. However, this addition may decrease the lauded sustainability of rammed earth construction due to the high embodied energy of cement. Designers choosing between SRE and RE should consider climate, structural requirements, durability, and sustainability when making their decision.
The rammed earth technique may be one of the oldest known construction methods, but it may be worth investigating updating it for modern times. Being an environmentally-friendly, strong, and even aesthetic material, rammed earth has a lot of potential for the future – just as much as it was a staple of the past.