Last Updated: Jul 10, 2021
According to the Australian government, “embodied energy is the energy consumed by all of the processes associated with the production of a building, from the mining and processing of natural resources to manufacturing, transport, and product delivery.” While certain home construction materials (such as wood) tend to have a lower embodied energy rating than others (such as aluminum or other metals), the energetic cost of transporting heavy materials long distances is a hidden ecological cost of the homes we live in. Building the walls and foundations of your home from the soil that you excavate on-site, however, is an innovative (although not new) technique to reduce your house's embodied energy dramatically.
Rammed earth is an ancient building technique with a modern appeal to homeowners looking for a beautiful, durable, and sustainable construction alternative. We recently talked with Clifton Schooley, a green building professional specializing in insulated rammed earth construction. Clifton owns and operates a rammed earth designing and building company in Canada and has experience with this sustainable construction alternative in several different parts of the world.
Rammed earth is a natural construction technique that involves compacting a damp mixture of soil with correct proportions of clay, sand, gravel, and occasionally a stabilizing material such as cement. This soil mixture is placed in formwork or temporary frame for the durable and well-braced wall and then compacted, usually to about half its original height. While the process of compacting the wall used to be extremely labor-intensive, most rammed earth builders today use pneumatically powered tampers to quicken the process.
Clifton adds that “modern rammed earth walls are composed of stone, sand, clay, silt, color pigment, and cement that is blended with water to make a damp mixture that is packed inside wooden formwork in layers. The walls are stone-like after 24 hours of curing.”
While there is historical evidence that rammed earth construction was utilized in ancient China thousands of years ago, this construction technique was also widely utilized in the early years of the United States. Historic buildings such as the Borough House Plantation in South Carolina were constructed from massive rammed earth walls. A U.S. Department of Agriculture Bulletin published in 1926 encouraged people in rural areas to consider rammed earth construction as an affordable and natural housing alternative. Today, this natural construction alternative is beginning to make a comeback.
Rammed earth walls have excellent thermal mass capabilities, meaning that they absorb heat during the day and slowly release that heat during the night. However, the insulation properties of earthen materials are generally poor compared to other construction methods. Clifton's company specializes in creating insulated rammed earth walls that achieve an R-value of 33, which is on par with the average for similar stick-framed houses in the United States.
“In Canada,” Clifton explains, “we embed rigid insulation inside the walls during the building process to increase the thermal performance of the walls. The R-33 rating is derived from the following: in a 24" wall, there is typically 4" of insulation at R-28 and 20" of rammed earth wall at R-5 (.25/ inch).” While insulated rammed earth walls are great for colder climates, they also “can be used in warm climates as well, for keeping the cold in when you need air conditioning.”
Clifton says that “the main benefit of the walls is the feeling you get by admiring their beauty.” Rammed earth walls are generally extremely thick, allowing for unique entranceways, thick window ledges, and other design opportunities. The natural pigmentation from the clays used in the construction process often creates streaks and contours of different natural-colored earthen pigments that resemble the earth's sedimentation lines.
Clifton explains that rammed earth construction can be combined with house design, solar orientation, footing design, window locations, roof overhangs, and heating systems to create a home with high thermal performance in terms of energy efficiency. Rammed earth homes are extremely durable and low maintenance, as you are essentially building a home that hardens into solid rock.
In terms of durability, cement stabilized rammed earth reportedly can withstand compression forces up to 40 megapascals, which makes it as strong and as durable as concrete while using much less cement. “Cement is used to not only act as a binder—as it does in traditional concrete—but also stabilizes the clay from expanding when water touches it. This gives the wall superior durability and even allows the walls to be submerged in water without any loss of structural performance.”
Clifton adds that properly built rammed earth walls can be completely load-bearing, removing the need for a separate timber frame structure. “It is reasonable for a 2' x 2' pillar to be able to support as much as 144,000 pounds, which is far more than needed.
In terms of ecological sustainability, rammed earth homes have a deficient embodied energy rating. The main material for the construction of the walls is sourced from the building site. Clifton's website also mentions that rammed earth homes are extremely fireproof, can be engineered for earthquake-prone areas, reduce demand for harvesting timber, have a high sound resistance for optimum acoustic design, are free of fungicides and pesticides used in commercial lumber, are insect proof, and can improve the indoor air quality of the home.
While many local building codes around the country are not receptive to alternative and natural building techniques, Clifton says that “these homes are permitted under the building code in Canada and the US. They usually don't have specific codes written for them but are allowed under a section that allows for unconventional methods. An engineer’s stamp is usually needed.”
In terms of cost, “upfront they will cost about 5-10% more than a custom stick-built home of similar interior quality. But, once you factor in life-cycle costs, reduced energy usage, less need for maintenance, etc., rammed earth homes cost less than conventional homes.”
Insulated rammed earth homes are environmentally appropriate everywhere that soil is present. Besides being aesthetically enchanting and incorporating unmatched strength and durability, rammed earth construction also has the ability to decrease the carbon footprint of the home you live in.
Tobias runs an agroecology farm and a natural building collective in the mountains of El Salvador. He specializes in earthen construction methods and uses permaculture design methods to integrate structures into the sustainability of the landscape.