In response to some of the challenges of climate change, the building industry is turning to some throwback techniques to reduce site impact, but also create “thermal” structures that promote passive temperature control. Heat is not the only environmental challenge that we face. There are also major considerations on how structures can endure wildfires, earthquakes, hurricanes and tornadoes.
One such ancient technique is rammed earth. This uses a subsoil mixture poured into a braced form in layers. It is then compacted by 50% of its volume with a tamping device before the next layer is added until each multiple batches forms a wall. Similar to a poured concrete wall, compacting the material and reducing air pockets and its drying time are part of what forms its strength.
Modern day rammed earth builds employ traditional footings or a reinforced slab as the foundation. Additionally, it utilizes the soil that has been excavated from the site as part of the mixture poured into the forms that use plywood or timber to form the walls. The wood is removed after the desired height is achieved and must be worked with immediately if a texture is to be applied. This is because the soil mixture dries quickly and becomes too hard to work with if hardened.
Rammed earth is a technique that has been excavated by archaeologists on almost every continent and in regions that range from arid desert to tropical. Examples of these structures surviving for thousands of years are a tribute to the endurance of this technique. A watchtower in China used in the Silk Road trade routes formed with the rammed earth technique in early 200 B.C. can still be seen today.
Many examples of these inspiring buildings using this technique have endured for thousands of years and have been found in Neolithic sites such as the Fertile Crescent. Much is being done to protect these sites so they can be studied to inform us about their longevity and durability.
Despite its ancient roots, the rammed earth technique has been employed in building some modern masterpieces all over the world. Whether as a portion of the structure or to create all the walls, this technique is growing in popularity.
Depending on the clay content of the wall, rammed earth is also effective at regulating moisture and naturally avoiding mold growth. Concrete, its counterpart, is much more dense and therefore prone to mold conditions if additionally protective materials are not applied. As the clay content allows the structure to breathe, it both reduces moisture buildup and significantly promotes heat retention. The density of the walls makes it an inherently fire resistant build, termite resistant as well as a natural sound barrier.
The utilization of the building sites subsoil both reduces waste, energy and the costs associated with transporting build materials. Unlike concrete builds, rammed earth utilizes aggregates found in the soil that are added to the mixture that is poured into the walls. Its density and thickness are what supports a thermally dynamic build, which takes up to 12 hours for heat to penetrate to the interior.
Furthermore, the wood used to form the walls can be reused on future builds cutting the cost of timber, which has as much as doubled in price. Cement production produces 1.5 tonnes of carbon dioxide per ton, making rammed earth a much more eco-friendly option.
Downsides of rammed earth
While there are some detractors in all building techniques, rammed earth has a comparatively short list. A good working knowledge of the soil types is a necessity for success. Colder climates will require insulation, thereby negating the natural finish on interior walls and, like concrete, once a wall is built, it is hard to augment.
Because of these detractors, it may be hard to convince a bank or lender to fund the project. But as we learn more about alternative builds and see them successfully implemented, these road blocks could be removed.
With necessity being the mother of invention, builds that help treat our planet kindly and support us living with inevitable ecological changes are a must. The lessons learned from this ancient technique make the rammed earth build a modern day sustainability dream.
Images via Iwan Baan, Rory Gardiner, Edward Birch and Cade Hayes