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Best Green Houses:

Going Native

Employing a proprietary rammed-earth structure, an Idaho home expresses its local identity from the ground up.

By David Sokol
January 2013
Photo © Kunz Photography

When a pair of high-powered lawyers requested Ward + Blake Architects to design a four-bedroom residential commission in Squirrel, Idaho, cross-examination ensued. The clients had pictured a Tuscan-style villa situated on 160 acres of former agricultural land they had purchased in view of Grand Teton. The Jackson, Wyoming–based architects launched a passionate defense that the prospective building should relate with its high valley location much more intimately. Principal Mitch Blake recalls, “It dawned on me that the house should spread out in a linear fashion across the sight to fit into the natural landscape. We discussed sod roofs and the way they link a house to the site, as well as thermal-mass walls like concrete and rammed earth.”

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Pairing rammed-earth construction to the sod roofing was the most native response to the site’s original meadow condition. “We have a mantra that we take our cues from the land. We think that using indigenous material from the existing terroir is one of the best ways to link a building to its site and locale,” Blake’s fellow principal Tom Ward says. “When considering the colors of eastern Idaho, it isn’t vegetation that provides the landscape its color but rather the earth that is visible between plant material. By using earth to build, you have a visual link to the site and its geology.”

Comprising soil grains with just enough clay to consolidate the mix, plus a negligible amount of Portland cement, the ingredients for rammed earth can be mostly harvested from the construction site and then inserted into the datum directly. Ward concludes, “The blurring of the manmade versus the natural becomes compelling and almost automatic.”

In addition to architecture, Ward is the inventor of a special rammed-earth construction process known as Earthwall. These walls are typically 18 inches thick and include post-tensioning steel that absorbs out-of-plate loads. Without the reinforcement, an earthen wall is strong in compression and weak in tension, meaning that it could not resist seismic activity on its own.

With an okay from the lawyers, who were already familiar with the material from a seminar they had attended, the design team proceeded to rethink their house in Earthwall. Yet that change of course also transforms the project’s design strategies. “This type of construction requires certain approaches,” Ward explains. “Being a relatively weak heavy building technique, one necessarily places it onto the ground. Expression of electrical and plumbing is different, as well, since these systems can’t be installed in walls that require pneumatic tamping.” And because rammed earth is porous, the designers would have to take particular care about moisture contact.

A certain aesthetic is inherent to the material, too. The soil’s multicolored stratifications do not recommend much geometric flourish, for example. Ward adds, “These structures possess a sense of permanence and timelessness, and the earthy component could be overwhelming if not offset by additional building materials.”

In Squirrel, Ward + Blake encountered a soil that possessed a desirable color, but which contained too much silt for the structural system. So, to enhance the mix, crusher fines—stone fragments slightly larger than sand, which are a waste product of gravel making—were sourced from a nearby rock crushing facility. While the construction crew had some experience erecting a rammed-earth wall prior to this project, Ward says that the labor-intensive process requires only several hours of training beforehand.

The resulting home measures 6,000 square feet, and the simple arrangement of forms provides counterpoint to the intricacies of the exposed soil. The very sensitive material combination includes selectively placed swaths of cedar and concrete cladding, whereas interior accents include a fireplace assembled of stone from an abandoned schoolhouse. “The client also purchased an old barn, and we used the siding on all of the sloped ceilings and soffits throughout the house,” Blake adds.

“When used as finished walls inside and out, the rammed earth has more integrity than other types of walls,” Ward observes. “When the primary material is both look and feel, the experience is profound, visually and acoustically. There is an overall sense of calm.” With their minds dramatically changed, the clients have enjoyed the house’s acoustic barrier against the valley’s whipping winds.

Interior climate also contributes to the placidness of Earthwall 2. Rammed earth, like any massive masonry type, undergoes thermal lag, retaining the sun’s energy during the day and releasing it slowly at night. Ward + Blake underscored this ostensible R-value by adding foam insulation (to the tune of an R-60 rating in the roof), specifying double-pane thermally broken aluminum storefront windows with Low-e coating, pouring concrete floors for extra thermal mass, and installing radiant heating from a ground-source heat pump and energy recovery ventilators.

To that end, Earthwall 2 takes advantage of all the strengths of its location. Site considerations prompted the use of northern-facing operable clerestory windows and floor-to-ceiling glass on the house’s southeastern exposures. And when the wind isn’t too strong, the clerestories work in tandem with ceiling fans—not to mention the south-to-north thermal cycle—for deeply penetrating natural ventilation.

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