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.
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.
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.
