As part of the 1987 International Building Exhibition IBA Berlin 1987 , in one of the most attractive inner-city residential locations in Berlin-Tiergarten, maisonette houses were built on the Landwehrkanal and were called "Okohaus". These three atypical residential houses were built with ecological principles in housing construction and were being tested for their feasibility and economy. The concept and planning of the structural and supply infrastructure came from Prof. Frei Otto, a father of ecological architecture in Germany. Each house was individually planned by individual builders and their architects under the conception and guidance of Frie Otto.
The site is situated in a fallow land surface in the vicinity of the Berlin Wall. Frei Otto suggested "a three-dimensional garden city" with low density and private use of public green. He developed two skeletal structures made of concrete with a width of about 35 m and about 60 m in height positioned on solid pillars. Despite its stiff and raw appearance, the deliberately open structure was to be customized by the inhabitants themselves.
In order to make this social and collective project sustainable, an article was published in local newspapers to attract potential "co-builders and co-participants" - a call which was immediately followed by a great number of applicants. "From the outside, all you could see was a wild overgrown piece of land", recalls Manfred Ruprecht, who joined the experiment at an early stage. "Spontaneously I said to my wife: this is where I would like to live!"Although many backed out after discovering that the overall costs and the duration of this "multi-storey gardens and living" project were uncertain, a building community of 18 families was finally created. "It was interesting - for my family and for myself as an architect - to be able to develop the design of my own house, according to my own needs", explains Jurgen Rohrbach.
The community of users "had an agreement that if one of them would have financial problems, the others had to stand in for him, in order to keep the project safe. Budget management was a big challenge for all. The individual inhabitants had to invest more than they had expected but also the big concrete structure had to be built in a cheaper version of what was planned at first, in order to keep within the social housing budget."
The building designs were made by 9 different architects who pushed the two-storey buildings - like drawers on a shelf - into the infrastructure. The detached houses seem to be stacked one on top of the other / pushed one below the other / installed or expanded. This was possible because the lower houses do not have to support the upper ones. The reinforced concrete infrastructure was very similar to tables standing on top of each other and gave the planners structural freedom within a given framework. The scarce inner-city building land could thus be optimally used. The idea of the city plots stacked on top of each other has been repeatedly executed in architectural history but what was special and new about this project was the consideration of ecological construction methods for the individual houses and the careful insertion of the project into an ecologically valuable property.
A qualified coordination of the individual designs was deliberately not carried out. There was only one appointment when all architects and builders inserted their 1:50 models into the infrastructure model for an afternoon appointment. The result was an anarchist architectural language with harmonious and disharmonious passages, depending on whether communication between neighboring planners had taken place or not - a "patchwork". The realization of the houses required a pretty perfect detailed planning, since the infrastructure specified by Frei Otto was fixed. The organizational construction process was also a challenge - without overarching coordination of the 18 individual builders - because it was quite possible that the upper house had already been built, before the one below was not even started.
It was an advantage for So.li.dar-architekten, a Berlin based architecture firm, that were commissioned by four individual builders and were closely cooperating with architect Martin Kuenzlen who also planned four houses. For the benefit of the builders, some construction measures could be better coordinated for at least these eight houses.
Constructional compromises were to be found, for example: Due to the desired / required light wood construction of the upper building of the five-storey residential building, the "reinforced concrete table edges" had to protrude at each plateau level (fire protection replacement measure), which logically led to thermal bridges that were perfect in terms of building physics and had to be dealt with costly. Another weakness in the joint venture project at the same time, the so-called residential shelf on Admiralstrasse (Berlin-Kreuzberg), shows that this weakness in the concept could be solved in a different way - albeit with loss of the individual appearance of the individual apartments.
Learning from Okohaus
The "Okohaus" as a complete body of work shows that most individual housing construction - whether funded or financed freely - are also possible in multi-storey housing construction with taking ecological construction methods into account, and that switching to single-family house areas on the outskirts of the city does not have to be an inevitable decision.
Frei Otto's anti architecture ideology and his resistance to forms of dwelling that disregard the desire of individuals, is evident in the Eco houses. The future residents planned their own building which included 50 one- and two-storey houses. Throughout the process advice and consultations were had with eco-architects, garden designers and energy experts - making sure that all the guidelines for social housing were still met. The final design includes solar panels and generous glazing, to harness solar energy, while the remaining buildings have green surfaces.