BAUBOTANIK: Building Architecture with Nature

Presentation at the 1st European Green Urban Infrastructure Conference, Vienna, Nov. 2015


Future oriented urban development concepts should maximise the quality of life for the inhabitants and at the same time minimize negative impact on the environment. A frequently used appropriate instrument to achieve this goal is to create big, ecologically effective open space, to plant as many trees as possible and to preserve old tree populations. Especially those have a huge positive impact on the urban climate by shading sealed surfaces and thus avoid the formation of heat islands, improving air quality and evaporating rainwater immediately to return it into the atmosphere. Although all these positive facts are well known and highly accepted, trees are likely to have hard times in planning and implementation and are often sacrificed for other priorities. In short, the dilemma is that trees with their need of space are in competition with the densely built up areas of the city. But at the same time density is a prerequisite for many urban qualities: Only if facilities for housing and working, schopping, culture, education etc. are in close connection to each other a “city of short distances” and an “urban lifestyle” can emerge.

Yet we shouldn´t reduce trees solely to their ecological effect, but also see their aesthetic qualities. With their big canopies they have a high spatial presence and therefore are ideal elements to structure streets and squares. They are contrasting the hard and dead surfaces with liveliness and multi-dimensionality as well as they relativize the dimensions of tall buildings and bring them closer to human scale. This positive effect on the psyche and thereby the health of people is scientifically proved:  Having only 10 more trees in a city block, on average, improves health perception in ways comparable to being 7 years younger. (Kardan et al., 2015) So it is no surprise that the inner city parks of increasingly dense cities are crowded on weekends and that more and more urban dwellers seek for nature in their free time. Simultaneously, European cities grow because of their attractiveness as a place of residency and work. City and nature seem appealing to people in the same degree. Already in 1927 Kurt Tucholsky described this apparently irresolvable contradiction between city life and nature in his poem „Das Ideal“ („the ideal“) that is frequently quoted by architects:

 „Ja, das möchste:
Eine Villa im Grünen mit großer Terrasse,
vorn die Ostsee, hinten die Friedrichstraße;
mit schöner Aussicht, ländlich-mondän,…“

(“Yeah, you’d like that:
A villa in the countryside with an ample terrace,
faces the Pacific, backs up to Central Park
with a nice few, rural and glamourous”)

How attractive especially trees are, becomes apparent when you look at children climbing into the canopies, hiding behind leaves and swinging on branches eagerly. The desire to transfer these qualities of trees into architecture is expressed in the tree house, which is neither a new nor an obsolescent idea. We can find examples in very different cultures and more and more also in contemporary architecture. Very special kinds of a treehouses are the so called „Tanzlinden“ that have been widely spread over Germany and beyond from mediaeval times to the 19th century and partly still exist. (c.f. Graefe, 2014) By forming the branches of lime trees with elaborate horticultural methods and creating an inner green space in the canopy, here “tree” and “house” are merging into one spatial unit. In a similar way but primarily with a constructive approach, a tribe in Northern India, the Khasi people, is taking advantage of the growth processes of trees since centuries. In a process that lasts over generations they are interweaving the aerial roots of the Indian rubber tree to merge them into framework like structures and living bridges spanning up to twenty meters wide canyons and rivers emerge.


Left: Living root bridge of the Khasi people (photo: Patrick Rogers) Right: Tanzlinde Peesten (photo: Förderverein Tanzlinde Peesten e.V.)


Also the Baubotanik1 approach understands trunks, branches and roots as a „living building material“ and develops  the idea of merging buildings and trees into a modern form of living architecture. Baubotanik buildings emerge through the interaction between technical joining and biological growth (c. f. Ludwig, 2012). Trees and parts of trees are trained, connected with each other and combined with not living elements to be transformed into a biological-technical system. Thereby characteristics and functions of these elements blur: Biological characteristics are transferred to the building while technical functions of structural elements are adopted by the growing material. 

Fusion of trees and buildings in Baubotanik architecture (image: Ludwig.schönle)


This is demonstrated by the 2005 realised Baubotanik Footbridge1 where technical columns are replaced by bundles of living willows taking over the main supporting functions of the load bearing structure and thus being essential parts of the construction. At the points where these living pillars were connected with the handrails, the stainless steel pipe is now completely overgrown and incorporated in the tree trunks. Such a form fit between non-living and living elements wouldn´t be possible solely by technical joining. And the building as a whole has characteristics that normally are typical for plants: Throughout the seasons it shows tender shoots in spring, forms a dense green space in the summer and after the colourful autumn the geometric structure and the technical characteristics of the steel grates appear in the winter.  Year by year it gains mass, becomes denser and more stable because many of the willow rods merge into a solid trunk through secondary growth in circumference. Shoots sprout in irregular shape and density in both height and width and are kept in shape through trimming.  The appearance is an interaction of natural growing, environmental influences and maintenance measures   (c.f. (Ludwig and Storz, 2009); (Ludwig et al., 2012)

Development of the Baubotanik Footbridge in the course of six years. From left to right: spring 2005, spring 2006, summer 2006, winter 2007/08, summer 2008, autumn 2010 (photos: Ludwig)

Development of details (Baubotanik Footbridge, 2005 to 2012) (photos: Ludwig)


The footbridge impressively shows how trees and architecture merge in Baubotanik buildings. But this doesn’t bring the qualities of big trees into densely build urban areas and thus doesn’t solve the dilemma described above. Simply because of the sheer size of common buildings in cities the footbridge could not assert itself in an urban context. Furthermore the used willow species would suffer in the shade of tall buildings. To come closer to the urban scale and to create green buildings in the dimension of full-grown trees, the technique of “plant addition” was developed at Research Group Baubotanik. Thereby young trees are planted in special containers, arranged three-dimensionally and connected with each other in a way that they merge into one organism. At the beginning the plants are provided with water and nutrients individually and trained along a temporary scaffold. In the course of the further development, a self-supporting and load-bearing structure emerges by secondary growth in circumference and the temporary scaffolds can be removed. Above all the lower most plants that are planted in the ground develop an efficient root system and inosculations between all plants enable the transport of water, nutrients and assimilates from the bottom most root to the top most leaf. Therefore the roots in the pots become obsolete and can be removed. Now the plant structure is self-sustaining and as robust as a naturally grown tree. (c.f. Ludwig et al., 2009) 


Principle of plant addition (image: Ludwig)


The “Plane Tree Cube” is a prototypical Baubotanik building that was realized in 2012 for the State Garden Show in Nagold (South Germany) as an urban experiment and to demonstrate the plant-addition technique.  The three story building with a dimension of 10x10x10 meters was able to be used as a green viewpoint immediately after its erection. And due to its green volume that was present from the very beginning it anticipated many ecological qualities of decades-old trees. In this initial stage the young trees that are arranged in containers on six levels are forming green walls that surround an open space. Inside you can find three stories with all round maintenance walkways for the gardeners and visitor platforms on the west side,accessible via steel stairs. Once the plants have grown together and the containers can be removed, the maintenance walkways become obsolete as well. The whole construction is supported by vertical steel columns that are going to be removed once the plant structure is stable enough to bear all acting loads.


Left: Plane Tree Cube Nagold immediately after completion. Right: Visualisation of a potential situation in about 20 years.  (Images: ludwig.schönle) 


Developmental forecast of the Baubotanik construction, Plane Tree Cube Nagold (drawings: ludwig.schönle)


In the course of time, when the canopy develops, the inner space will become more and more closed to the sky whilst the lower part will become more transparent and show the increasingly knobby and thick trunks. When the area of the State Garden Show will evolve to a new urban quarter in the next years the Plane Tree Cube will be surrounded by urban houses and serve as a Baubotanik neighbourhood square. In contrast to these houses that will correspond exactly to the specifications of the architects drawings, the appearance of the Plane Tree Cube can only be designed as a vision or prognosis: There are environmental impacts that can´t be foreseen, possible illnesses and local influences like hail storms that will make some of the plants grow more vigorous whilst others suffer or die. These conditions require a way of thinking that deals with possibilities and probabilities. The Plane Tree Cube this reflects this in the redundant structure of the load bearing system. 

Above: Forecast of the spatil development, Plane Tree Cube Nagold (drawings: ludwig.schönle). Below: Joining of the plants  with stainless steel screws and development of such a connection shown at a test plant (photos: Ludwig) 


With its procedural character the Baubotanik approach comes along with questions of temporality: Which spatial qualities should we strive for in which moment? Which ecological performance has a building in its different developmental stages? How can we react on new facts and circumstances? Although a Baubotanik building is planned and erected, the architect loses his absolute design authority and the co-designer of nature. But this uncertainty also creates a curiosity that awakes emotions we normally don’t associate with architecture. The fascination for uncertainty is one of the driving forces for the contribution for the house of the future in Berlin by ludwig.schönle.1 As proposed in the competition announcement, the building should be designed as a “window facing the world of tomorrow” by exhibiting objects of which we do not even know today how they will look like. The proposal articulates the idea to express future architecturally in a Baubotanik façade that surrounds the whole building. A façade no one knows today what it will look like in the future. At the same time, this façade is an integral part of the climatic concept of the building: In summer the foliage is cooling the air by transpiration and is effectively shading, in winter it allows a maximum of solar radiation to pass and thereby is taking advantage of natural phenomena to create an integrated climatic concept. Towards the city, the building appears as a big artificially created tree.  Inside a wide ramp leads upwards along the tree-glass-façade offering the possibility to explore the canopy in different heights to the visitor. Through the rhombic structure that is at the same time technically constructed and naturally grown, the visitor can gaze over the branches and leaves moving in the wind.  Depending on season and direction, views to the Reichstag, the Kanzleramt or the main station are possible. The façade, often described as the “third skin” in architecture, becomes a voluminous third layer, which at the same time creates a new habitat. Namely living space for birds and insects that find their way back into the habitat of humans in this way. Therefore, Tucholskys desire for a “library surrounded by lonlyness and humming bumblebees” (  „Bibliothek und drumherum Einsamkeit und Hummelgesumm“) expressed in the poem “the ideal” (“Das Ideal”) seems to be within one's reach in the middle of Berlin.

Competition entry for the „House of Future“, Berlin (image: ludwig.schönle)



1) The term „Baubotanik“ arised at the Institute for Architectural Theory (IGMA) at the University of Stuttgart, where Research Group Baubotanik was founded and established as a profession and instutution comprehensive network by Prof. Gerd de Bruyn in 2007.

2) Realized  by Ferdinand Ludwig, Oliver Storz and Cornelius Hackenbracht

3) Competition by  BBSR ( Federal Institute for Research on Building, Urban Affairs and Spatial Development in Germany) 2012; third price


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