✕

For Roger Boltshauser, founder of Zurich-based Boltshauser Architekten, the 2008 Rauch House in Schlins, Austria, changed the course of his career. Codesigned with Martin Rauch, a European pioneer in the revival of earth construction, it was built almost entirely from soil excavated on-site. Since then, Boltshauser has been progressively pushing client boundaries with respect to low-carbon building techniques, in particular earth construction. At Kilchberg, just outside Zurich, his firm recently turned the dial up a notch when it completed a small apartment building—seven rental units, ranging from a studio to two-bedrooms—that uses both recycled fired bricks and unbaked earth block.

With its hillside views over Lake Zurich and the old city beyond, Kilchberg is at the upper end of the Swiss residential market, attracting the kind of wealthy occupants who drive Ferraris and Porsches. Fearing that those with such a social profile might be put off by anything too radical, the client rejected Boltshauser’s proposal for load-bearing earth and brick walls, instead preferring the standard Swiss solution of a concrete frame. “Faced with this situation, we aimed to minimize the frame and maximize the filling,” explains the architect. Using a post-and-slab system he likens to Le Corbusier’s 1914 Maison Dom-Ino proposal, Boltshauser designed a building that is reminiscent of another celebrated Corbu project, the 1955 Maisons Jaoul in Paris. Both Jaoul and Kilchberg display a similar combination of exposed structural concrete and tactile brickwork infill, but, where Le Corbusier changed bricklayer every few courses to achieve a roughed-up effect, Boltshauser used time-patinated 100-year-old clinker bricks. These were reclaimed from a demolished church in Cologne, Germany, 250 miles away, a distance “that’s about the limit for sustainability,” comments the architect. “We debated whether we should use these bricks, but decided to go ahead, to show that it can be done, because there’s no brick-recycling industry in Switzerland.” Since modern mortars make it impossible to separate bricks without breaking them, Boltshauser specified a weaker mix, so the clinkers can be recycled again when the time comes.

1

2

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.

3

4

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.

Click plan to enlarge

Click section to enlarge