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With views over Lake Zurich (1), the building uses reclaimed brick on the outside (top of page) and unfired earthen brick on the inside (2). Photos © Kuster Frey, click to enlarge.

While the external vocabulary of the Kilchberg apartments may seem familiar, inside, in the context of speculative housing, they appear far more radical, since almost every surface has been left raw: concrete floors are subtly tinted red and polished to look like terrazzo; concrete bracing walls are exposed; and the earth-block inner surface of the external envelope (a classic cavity-wall system more than 20 inches deep and providing excellent thermal inertia) is also entirely bare.

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The floors, in polished concrete, have a subtle red tint (3 & 4). Photos © Kuster Frey

Molded by the Geneva firm Terrabloc from soil dug out to build the foundations, the unbaked blocks also served for construction of internal partitions. Where loads are light, they are made from pure earth, but when subjected to greater compression, the blocks are stabilized by the addition of 4 to 5 percent cement. To ensure they can breathe, they must not be painted or plastered, a condition that had far-reaching design implications: not only did the architects have to draw the placement of every block in advance, they also had to detail services from the outset, with wiring run through metal tubes and plumbing restricted to specific areas. Earth is also present in the mortar used to mount the blocks and in the off-white plaster covering the concrete ceilings, specified to make the rooms more luminous and to contrast with the dark beige of the pressed blocks.

The interior’s earthen bricks are left bare. Photo © Sandro Livio Straube

In his bid for sustainability, Boltshauser keeps things low-tech when possible, so he eschewed mechanical ventilation at Kilchberg, except in the basement parking garage. Heating, as one would expect, is geothermal, while solar panels cleverly double as sun shades on the top-floor balconies. Since unconventional building methods cost a little more, the onus was on the architects to make the plan as efficient as possible to squeeze in extra rental space. Moreover, Boltshauser’s experiments in an architecture of expressed materials and tectonics create a strong aesthetic that might not be to everyone’s taste (to hang pictures on their mud-brick walls, residents may only drill holes into the mortar). Nonetheless, despite the client’s fears, all the Kilchberg apartments found occupants within two months. “The tenants really like the look of them,” comments Boltshauser. “I think they see it as an alternative way of living.”

Although the Kilchberg building marks a huge advance from the early days, when “clients wanted none of our environmental ideas, however hard we pushed,” Boltshauser still feels it is a compromise. The next challenge, he says, is to move beyond Kilchberg’s artisanal scope to demonstrate that much larger buildings can be constructed using alternative methods. Only then, he believes, might we usher in a paradigm shift at an industry-wide scale.

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