Rammed Earth: An Ancient, Sustainable Construction Material

Examples are Everywhere

Olnee and EarthHouse Australia specialize in high-end, modern homes constructed with rammed earth. Vo Trong Nghia Architects designed a house in Hanoi featuring walls made from different types of rammed earth and gabled roofs incorporating planters used to grow fruit trees.

Rama Estudio used thick rammed-earth walls and large windows to prop up the slanted roof that covers this residence, built among a eucalyptus plantation in Ecuador. Red and grey tones run through the rammed-earth walls that Feldman Architecture used to build a farm retreat in California’s Central Valley. The architecture studio Blaanc used layers of compacted earth to form the walls of this house in a vineyard in Portugal.

CCS Architecture in San Francisco designed and constructed a Palo Alto residence using rammed earth. An exterior wall formed from soil excavated on site is visible below the ipe-wood-clad volume on the second level. Throughout the interior of the house, exposed rammed-earth walls display their unique “coursing” or horizontal striations. In some places, clerestory windows were set into the earth walls, bringing earth and air together to frame views and allow in light.

In the Texas Hill Country near Austin, Furman + Keil Architects renovated an existing rammed-earth barn into a family residence. The process posed intriguing challenges, the architects have said: “how to preserve the integrity and presence of this unfinished structure while providing conveniences of modern life. The conversion treats the rammed earth walls with respect, touching them delicately and constructing multi-level living quarters inside the larger volume. Much like a cabinet inside of a shell, a wood mezzanine takes advantage of the spaciousness inside the barn. Steel windows and doors infill openings in the rammed earth, contrasting with the two-foot thick walls.” 

The architectural firm Carney Logan Burke created a rammed-earth home addition in the Wyoming countryside used as a studio and office. The architects used rammed earth to construct the south and east walls of the addition. They enhanced the striated, earth-tone walls with bronze-clad floor-to-ceiling and slot windows, bonderized steel accent walls, and a copper ceiling. Using rammed earth for the addition ensured the studio would have high thermal mass, providing thick insulation for cold winter months. 

Rammed Earth Defined 

Using rammed earth to construct homes isn’t new. Rammed earth (also known as taipa in Portuguese, tapial or tapia in Spanish, pisé (de terre) in French, and hangtu in Chinese) is an ancient construction method dating back to the 2nd millennium B.C. in China. Parts of the Great Wall of China were constructed using this technique and are still standing more than 2,000 years later.

The technique has been used to build foundations, floors, and walls using natural raw materials such as earth, chalk, lime, or gravel. Rammed earth is simple to manufacture, non-combustible, strong, and durable. Rammed earth also has excellent thermal mass capabilities, meaning the material absorbs heat during the day and slowly releases the heat at night. Unlike compressed earth blocks, which are similar, rammed earth defines the entire structure that is built versus individual pieces.

The Australian company Rammed Earth Construction also cites other advantages, including “temperature and noise control, strength and durability, low maintenance, fireproofing, load-bearing and pest deterrence, as well as its beauty and the pleasure of building with natural and environmentally sound material.” Is it any surprise that rammed earth has been revived as sustainable building material today? But don’t start digging yet.

The Construction Process

You’ve got a site, you’ve got dirt. First think about testing your soil. Take a sample to a geotechnical lab at your state or university agricultural department. Have the lab test the sample's compressive strength. According to the standards in earthen-material codes, the sample should be able to withstand a pressure of 300 pounds per square inch (PSI). Other materials that get mixed in include gravel, sand, silt, color pigment, clay, and cement. The mixture that will become rammed earth also contains water (no more than 10 percent).

According to Clifton Schooley, a sustainable building professional specializing in rammed-earth construction in Canada, the “damp mixture is packed inside wooden formwork in layers.” Think of the buckets used to make sandcastles, except the house, needs rectangular wood forms of marine-grade plywood or steel. Walls are built in panels of approximately 3.5m in length with flexible joints to comply with building rules requirements for masonry structures.

Four to six inches of the mixture are shoveled and rammed into the form, by hand or by machine. Professionals in the rammed earth construction often use machines hooked up to air compressors, which tamp down or ram the earth. Quentin Branch, a rammed-earth builder, and owner of Rammed Earth Solar Homes told How Stuff Works that “When you first start ramming dirt, it makes a dull sound, but when it's adequately tamped, it will change to a ringing sound. Once the earth is ringing, then you can add the next 4 to 6 inches of soil. It is possible to ram too much, which will cause stress on the wooden form.”

He adds that “Once a section of wall has been constructed, the form is dismantled and moved to the next section, and the process begins again. Windows and doors are installed by ramming earth around separate forms that serve as placeholders. Once the earth has been cured (or set) around the placeholder, the form is removed and the earth will hold without it.”

According to Schooley, “The walls are stone-like after 24 hours of curing.”

Beautiful and Sustainable Benefits

Your Home, a website sponsored by the Australian Government, recommends that stabilized rammed earth walls be finished with a clear water-repellent coating. Non-stabilized earth walls should be protected by eaves or overhangs. Sometimes walls are wire-brushed shortly after being released from the formwork, which eliminates the lines or joins created by forms and can result in an appearance close to monolithic sandstone.

The pigmentation and texture created in the rammed earth from clays and aggregates used in the mixture can result in streaks and striations, contours, and colorations. The aesthetic appeal created in the walls is one of the benefits homeowners with rammed-earth homes enjoy. As Clifton has said, “the main benefit of the walls is the feeling you get by admiring their beauty.” Rammed earth walls are also thick, which allows the architects and builders to design and fabricate dramatic entranceways and thick window ledges. The thick walls also add to the feeling of quiet and comfort in the home. 

The rammed-earth home’s foundation, roof, electricity, plumbing, and decorative features are installed in the same way as other houses. Architects and builders specializing in rammed earth often combine such strategies as siting and solar orientation, window location, roof overhangs, and heating and cooling systems in a home’s design to maximize the home’s sustainability and minimize its energy requirements.

Many local building codes around the US aren’t receptive to alternative and natural building techniques, but rammed-earth homes are actually permitted under the building code—usually within the sections for unconventional methods. In terms of cost, as we mention in another Rise story on the benefits of rammed earth construction, “upfront they will cost about 5-10 percent more than a custom stick-built home of similar interior quality,” Clifton says. But factor in the life-cycle costs reduced energy use and reduced maintenance, and rammed earth homes—in the long run—cost less than conventional homes.

From a sustainability standpoint, rammed earth construction is quite beneficial to both the planet and the homeowner. And from my personal experience, it’s cool, quiet, comfortable and beautiful.