Cast & Character: Building a Home With Cast Earth Construction
(Page 2 of 3)
May/June 2001
By Joyanna Laughlin
Cost Efficient
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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.