Set in stone

In the push to build with materials that are energy-efficient, high-tech, and still esthetically pleasing, we often overlook the obvious because we are so bent on developing something new. Why should we look at yesterday’s solutions? We’re innovating! Well, sometimes the most sustainable solution is right under our noses, and has been there for a long, long time.

Once upon a time, buildings were made exclusively from local materials. In Switzerland, that meant wood and stone. Now most Swiss buildings are made with concrete, occasionally sporting a thin veneer of natural stone for esthetic purposes. For his EPFL master’s project in architecture, Stefano Zerbi designed a building made with massive blocks of stone from a local quarry in his native canton of Ticino. The project, however, generated more questions than answers in his mind. Why wasn’t local stone being used more often as a building material? And why were Switzerland’s stone quarries languishing? Under the guidance of Professor Luca Ortelli, and with the collaboration of Professor Aurèle Parriaux from ENAC’s Engineering and Environmental Geology Laboratory, Zerbi decided to pursue these questions further.

Local stone is a sustainable building material because it’s tied to a region’s resources, explains Ortelli. Unlike concrete or wood, massive blocks of stone hardly degrade or change over time, and they’re fully recyclable. Stone doesn’t have the embedded carbon footprint of concrete, particularly steel-reinforced concrete, and it is esthetically pleasing. In fact, many modern concretes try to imitate the look of natural stone. Zerbi and Ortelli suspected that architects didn’t consider using massive blocks of stone because they simply weren’t aware it was a viable option. Perhaps if they had access to more information about local sources, this could change.

With Swiss National Science Foundation (SNS F) funding in hand, Zerbi took to the road. He visited all of Switzerland’s major stone quarries, taking an inventory of everything from the geological characteristics of stone produced to the quarries’ exploitation statistics and contact information. He made illustrations of the extraction method used in each quarry and took photos, and then assembled all this information into a reference booklet for architects and builders.

Zerbi found that many of the larger quarries were not using all of the stone they extracted. An increased demand for large blocks of massive stone, which, unlike thin veneers, don’t have to be homogeneous, would make it possible to exploit these quarries’ resources more fully. We tend to think of natural stone as hugely expensive, but massive stone is much cheaper than veneer, says Zerbi. “When you reduce the number of cuts, the cost goes down.”

Another important consideration is earthquake resistance. Could a building made with massive stone blocks stand up to a major tremblor? Ortelli and Zerbi knew they’d have to demonstrate this if they wanted to convince architects to build using stone. To clear his hurdle, Zerbi collaborated with Pierino Lestuzzi and Katrin Beyer in EN AC’s Earthquake Engineering and Structural Dynamics Laboratory to test a simple mortar construction, a project that was incorporated pedagogically into the Master’s Program in Civil Engineering. “Three weeks after the start of the test, it was in great shape,” says Zerbi. “Every week, the pressure was increased and it performed remarkably well.” Zerbi and Ortelli’s meticulous interdisciplinary research makes the case: from the resource level to the building itself, massive stone is a good, solid, sustainable solution.