When Jan Johnson saw a newspaper article on earth houses and decided she wanted one, little did she know that she would end up owning a home in the forefront of sustainable building technology. Jan, a pediatric occupational therapist, cut out the article and tacked it up in her office. Twelve years later, she moved into her dream home, a 2,000-square-foot cast earth house with a 400-square-foot attached guesthouse in Prescott, Arizona.
Having spent time in Africa, Jan is familiar and comfortable with earth structures. She bought property in Prescott in 1997 and told her real estate agent that she wanted to build an alternative home there. The agent referred her to Michael Frerking, owner of Prescott-based Living Systems Architecture and Construction, who has been designing and building earth homes and buildings since 1975.
Cast Earth Construction
When Frerking suggested cast earth, a relatively new building material made with earth and calcined gypsum that requires less hand labor than adobe or rammed earth, only a couple of houses had been built with it. But Jan was drawn to cast earth for several reasons. She liked the rich colors and beautiful patterns that can be created by adding pigments to naturally light-colored cast earth walls. Second, earth for the house could be “harvested” from a local lake that collects runoff sediment. And third, the energy efficiency of cast earth homes can make them less costly to live in than conventional homes.
The design process began in fall 1997. Construction started in April 1998, and the home was completed in November 1998. Some of the design challenges included minimizing destruction of the site’s natural environment, situating the house to take maximum advantage of passive solar gain, and orienting the windows toward peaceful views of nature, not neighbors. The result intrigues and invites visitors without giving away its size or its secrets.
“My house reflects who I am,” Jan says. “I wanted it not to attract a lot of attention on the outside, but to be interesting looking, and then, as you come inside, it gets more interesting the farther you get into it.”
Three striking, curvilinear walls give a sense of peace, stability, and positive energy flow to the one-story floor plan that includes a living room, a dining room, a kitchen, three bedrooms, two bathrooms, and an office.
Jan’s house was built to vary an average of seven degrees between day and night and to vary throughout the year between sixty-two degrees Fahrenheit and seventy-eight degrees Fahrenheit without backup heating or cooling. According to Jan, the temperature in the house stays around sixty-six degrees Fahrenheit most of the time and never dips below sixty. Jan’s utility bills average between $80 and $90 per month for electricity and gas.
Minimization of heat loss and gain is the key. Although the twenty-four-inch-thick cast earth walls contain an integral insulation layer, it’s the inherent ability of the mass walls to retain and release solar energy that maintains the comfortable indoor environment. All the non-cast earth interior walls and the ceiling are insulated with blown-in cellulose insulation made from recycled newspapers. Concrete Insteel 3-D Wall Panels provide extra insulation. They also enhance the exterior walls’ structural integrity and function as a moisture barrier for the interior walls. A passive solar Trombe wall that looks like a large window is actually part of the energy efficient design. Behind the glass, a cast earth wall eight feet high and twelve inches thick absorbs the sun’s heat as it passes through the glass during the day and slowly releases it into Jan’s bedroom on the other side of the wall at night.
Maximization of natural light is another important design feature. Just below the roofline on the south-facing exterior wall is a light shelf, a passive solar feature that takes direct light from outside and diffuses it inside the living room, dining room, and kitchen, to make these rooms more comfortable and to help light them naturally. The light shelf, constructed of conventional wood framing, extends three feet outside the house from the exterior wall and also extends three feet inside the home’s living room and kitchen from the interior wall. Outside, it is covered with a bright white exterior roof coating and inside with bright white interior paint so that sunlight reflects off it and onto the living room and kitchen ceilings.
Currently, the cost to build a cast earth home is comparable to that of adobe and rammed earth. According to Frerking, building a 2,000-square-foot cast earth house costs about 15 percent more than a comparable stick-built house. Jan’s house cost $120 per square foot to build, and the cost rose to $133 per square foot when specialty light fixtures and appliances were included; the total cost was approximately $320,000. As the technology advances and multiple cast earth homes are built at one time, however, Frerking expects to see the costs come down.
Despite the cost, Jan recommends cast earth. “I wanted to have a house that didn’t use much wood and that I could retire in,” she says. She paid more up front for cast earth, but she’s recouping those costs in lower utility bills. “Now, no matter whether it’s good times or poor times, I’m comfortable,” she adds.