Lightweight 'triple-zero' house produces more energy than it uses

Overlooking the city of Stuttgart in southern Germany, a four-story modern glass house stands like a beacon of environmental sustainability. Built in 2000, it was the first in a series of buildings that are "triple-zero," a concept developed by German architect and engineer Werner Sobek, which signifies that the building is energy self-sufficient (zero energy consumed), produces zero emissions, and is made entirely of recyclable materials (zero waste).

Since the construction of the first triple-zero home, Werner Sobek's firm of engineers and architects, based in Stuttgart, has designed and built five more in Germany, with a seventh planned in France. The energy used by these buildings, including the four-story tower where Sobek resides, comes from solar cells and geothermal heating.

The most recent addition to the triple-zero series raises the bar for energy efficiency: It produces more energy than it uses, Sobek said. The one-story glass home, which seems to float in front of a backdrop of pine trees, "is a tiny power plant [which] feeds electricity into the public grid," he said during a lecture on his work on December 2. The lecture took place at The Cooper Union for the Advancement of Science and Art.

Sobek thinks that planners, builders and policy-makers must think about how to reduce the environmental impact of buildings at the same time that they try to reduce the footprint of the automobile and other industries. The building industry is responsible for 35 percent of the world's energy consumption and carbon emissions, and 50 percent of the waste produced in North America and Europe, Sobek said. His engineers and architects are working to reduce the energy required to maintain houses, office buildings, airports and bridges, as well the energy that goes into constructing and disassembling these structures.

Following the 1979 oil crisis, German engineers started to build "Passivhauses," or passive houses. These buildings retain comfortable interior temperatures without the use of active heating and cooling systems. Instead, passive houses receive warmth from sunlight through its south facing windows and underground air ducts in the winter, while the airtight seals prevent warm air from entering in the summer. But with the scant number of windows and 300 millimeters of thermal insulation, "you live like you are in a Styrofoam box," Sobek said.

Sobek strives for just the opposite effect of the Passivhaus, using thinner walls and bigger windows or, in the case of triple zero houses, all-glass walls. "I invented the so-called 'Aktivhaus' [or active house]—buildings which open your soul, which open your mind, which open your heart," said Sobek, who is also head of the Institute for Lightweight Structures and Conceptual Design (ILEK) at the University of Stuttgart and is the Mies van der Rohe professor at the Illinois Institute of Technology. These glass walls still provide insulation, however, because they are triple-glazed, meaning they have three layers of glass with air space in between the layers.

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