Green Building in Germany

The future of dwelling is alive. That is the belief of three architects from Stuttgart who are banking on a completely new building support structure: plants firmly rooted in the soil. In this way, houses and cities could literally grow into the skies. There are already “building botany” bridges and pavilions.

If it were up to Ferdinand Ludwig, mankind would one day live again in trees. The Stuttgart architect dreams of roofs and walls that consist largely of living ash, poplar and plane trees, firmly rooted in the soil. Whole forest-cities could then reach into the skies, cities whose leafy houses could, moreover, contribute to purifying the air. “Liveable houses made of trees are possible”, says Ludwig. “They are our declared long-term goal.”

Together with Oliver Storz and Hannes Schwertfeger, Ludwig forms the core of the research group “Building Botany-Living Architecture” at the University of Stuttgart. The three Ph.D candidates are the founders of a new architectural discipline, in which irrigation systems and hedge clippers take the place of plumb lines and trowels. Ludwig is in charge of biology and botany, Storz of the engineering and construction aspects, and Schwertfeger of the architectural theory.

When bridges grow roots

“Actually, we’re not utopians”, says Ludwig. “We only want to explore what is possible when trees are re-thought as building support structures.” What has been possible up to now may already be seen in numerous projects. The first masterpiece was a twenty meters-long bridge in a moor landscape at Lake Constance, where a classical support structure would not have been possible. Now there are also two pavilions, a bird-watching house and five prize-winning information towers on the island of Mainau.

They are constructed from thickly planted willow: from plants, that are well rooted, particularly thin, grow extremely rapidly and can be readily bred from cuttings. The plants, which grow high and crosswise, form a stable meshwork that, as far as possible, should only be cut and not broken or sawed. The “Bird-Watching House” is the first botanically constructed building with a roof and more than two storeys. Up to ten hobby ornithologists can observe birds from its nearly two meters high, 800 kilogram platform.

Intelligent willow

For Ludwig and his colleagues, plants are “more intelligent” than brick and concrete. They like to speak of “constructive intelligence” when talking about the evolutionarily developed advantages of their architecture. “Plants have learned to carry heavy loads”, says Ludwig. Their growing process optimises force and tension, and by contrast to technical building components they have no predetermined breaking-points. “Moreover, wood thickens at those points where it is heavily stressed”; the architects therefore train their building material to form knots at crucial supporting points by deliberately exposing it to strain. In contrast to classical building construction, where materials gradually become brittle with stress, a living building literally grows with its tasks.

In their projects, the three architects also use non-living technological materials. For instance, the bridge at Lake Constance is held together by polyester bands and reinforced by a stainless steel grid resting on a supporting structure of sixty-four bundles of withy. The “Bird-Watching House” is stabilized by iron rings. Altogether, the architects are concerned philosophically with a symbiosis of nature and artificiality. In Hannes Schwertfeger’s view, their buildings are “artefacts and living beings alike”. And as a matter of fact, nature vigorously continues building after the apparent conclusion of construction. Building becomes a continuing process.

Wildly exuberant surprises are as much desired as is the circumstance that the buildings look different in spring than they do in winter. “Our bridge”, says Ludwig, “can hardly be made out in summer for all the leaves”. Then the architects come again with their hedge clippers so as to cut open a passable area.

Living in the stranglehold of the tropical fig tree

In the meantime, Ludwig, Storz and Schwertfeger have also tested more complicated plants as building material. Willow has the disadvantage of being exceedingly thirty and sun-hungry. It also stops growing when it reaches four to six meters. The architects therefore are collaborating with a “Plant Biomechanics Group” at the University of Freiburg. In a greenhouse in the Freiburg Botanical Gardens, the researchers are experimenting with the plane tree, a resistant “city tree”, to discover whether building botany can also flourish in the shadows of urban high-rises. They use screens to filter out certain light wavelengths and make the plane trees grow more slender and more rapidly upwards than they do in nature.

Later maples, poplars and ash trees will be included in the experiments. Nor have the liana or the tropical “strangler fig tree” been forgotten. The latter is a parasite whose aerial roots slowly blast its host. If the host tree is replaced by inflatable tires, the wattlework could develop into a methodically grown, pressure-stable timber framework for columns or arches.

Fungi instead of wrecking ball

The three architects have already developed a building botany willow pavilion ready for the market: it can be ordered for the home garden on the Internet. As their next projects, Ludwig, Storz and Schwertfeger are planning two pedestrian bridges with a span of six meters in the Saarland, and a twenty meters long bridge over the river Neiße on the German-Polish border. But river-crossers will have to bring with them a natural degree of patience; in order to develop optimally a stable supporting structure, plants need time. The planned Neiße bridge will need seven years before it is fully grown.

On the other hand, plant buildings have a natural and not always calculable half-life. They can fall ill and die. A tree-house seldom survives more than a generation of inhabitants. Then worms, woodlice, fungi and bacteria would see to waste disposal, and wreckers would become unemployed.