“I don’t have a cellphone.”
Prof. Gernot Minke, Architect, Professor emeritus University of Kassel, Germany
Interview dated August 28, 2013 in his house in Kassel
Prof. Minke has published numerous books on building with earth and natural materials. He directed the Research Laboratory for Experimental Building at the University of Kassel for 38 years. In 2012, he retired. We wanted to know more about his research on building with earth, and also about his impression on the future of building with earth and natural materials in Europe.
After a four-hour drive from Berlin, we arrived in Kassel. It took us quite a while to find Prof. Minke’s house. It had seemed to be missing. There were just bushes where the house was supposed to be. It was only after a while that we saw a path in the bushes. The path led to a small door, and the door opened to a cathedral!
How did you get interested in earth building?
In 1979, I took a sabbatical to visit universities in America. I wanted to find out what was going on with appropriate, alternative technologies. Also, I visited Guatemala where my father was born. There I saw the earthquake damage of 1968, and the terrible kinds of emergency housing that international aid had built: houses made of prefabricated plastic elements, concrete slabs, and cardboard. I thought it must be possible to make earthquake-resistant houses with earth.
From emergency housing made of plastic to earthquake-resistant houses made of earth
When I returned to the University of Kassel, I received funding to develop, at the research laboratory that I had launched [a few years earlier], a rammed-earth structure stabilized by bamboo, which is flexible enough to absorb the kinetic energy of an earthquake. That was quite an innovative method.
We applied it to build a small earth house on a farm in Guatemala for a total material cost of USD 500. But nobody was interested in it. The house was too cheap. The owner of the Hacienda benefited from foreign aid (he had to spend USD 2 million per year) and wanted a bigger representative house. Local businesses were not interested either, since we didn’t have to buy anything, only a few screws and boards for the roof. It was very frustrating. So I went back to Germany and built my first house with earth here in Kassel, in an ecological settlement, in 1983. Eight years later, I built a second house for me, which is today my home. The rooms are vaulted with domes out of unburnt mud brick.
“You can make modern architecture out of mud?!“
When I returned to Guatemala, 25 years later, and showed people photos of my new earth houses, they couldn’t believe it. They said, “You can make modern architecture out of mud?!“
Because for them, earth is what the poor use. And that´s the main problem in developing countries. So my theory became: „You shall first build earth houses for wealthy individuals, for managers, for divas, and only then, for the poor“.
For 38 years, I was the director of this research laboratory in Kassel. We had run 50 research projects and built 30 houses out of earth, with only one technician and one scientific researcher, who were on a fixed term contract.
Did the environmental movement in the 1970s have an affect on you?
No. Not directly. Indeed, there was a big movement towards alternative technologies at the university level starting in the late 1970s and early 1980s. Of course, we read books from the USA, such as „Homemade houses” or „Shelter”. Some of us knew a lot about this movement in the States.
University of Kassel – 38 years of research on building with earth
Was the University of Kassel the first institution worldwide that did research on building with earth?
The University of Kassel had the first Research Laboratory of this kind, and the only one that carried out continuous research from 1974 to 2011 on building with earth. CRAterre in France had several research projects in the late 1970s, but Kassel was the only place that continuously carried out research and taught how to build with earth. We had about 2200 people, who are not even from that University, who took part to our introductory course on earth building.
Why did the research laboratory closed in 2011?
It closed due to a lack of suitable candidates, who needed to be both a good architect as well as a good researcher on this subject. Also the position of my technician was victim of mandatory job cuts, as stimulated by the finance minister. He was a key co-worker for me, as he applied all my ideas.
Another reason is due to the younger colleagues’ belief in high technology, For them, building with earth and straw had little relevance to [today’s] “modern” architecture. We completed our last research project in 2012, and my two technicians and I are now retired.
First discovery and results in the shower
What did you discover – what were the most surprising test results in your research on earth building? Did you expect those results?
The first thing was that earth, better than any other building material, absorbs humidity if the relative humidity is higher than 50%, and dissipates it when it is lower than 50%. In my first house, which was also an earth house, I was astonished to note that, nearly all year round, there was a steady measurement of 50% humidity. In the kitchen, after cooking, maybe it went up to 60-65% but one hour later it went down again to 50%. In the bathroom especially, I had never recorded more than 70% of humidity after a long shower, even with the door and windows closed.
I realized that fungus would not grow in humid rooms, like bathrooms, because fungus appears between 80-85% humidity. So my philosophy is: Earthened bathrooms are more hygienic than ceramic-covered-to-the-top modern bathrooms! (Because black mould sets in the joints and their spores are highly toxic). Those results were further confirmed at the research laboratory. We conducted hundreds of tests. This was in the 1980s.
Earth houses in the electromagnetic age
Another discovery that was important was that earth, as a massive building material, stops high-frequency electromagnetic waves better than any other solid material. Those tests were carried out by the research laboratory at the Bundeswehr Hochschule in Munich. The best results have been obtained on a green roof (which consists of 15 cm of earth and 24 cm of unburnt earthen bricks): the indoor electromagnetic waves were reduced by 99.99%.
We built a house for a client, who wanted an electrostress-free house, and measured that 99.6% of
the outdoor electromagnetic waves were stopped. The house has earthen vaults, a green roof and special windows that are covered with a thin metal layer. The windows were first developed in order to increase the thermal insulation, but we also noticed that they acted as a protective shield against electromagnetic waves. If you wish to use a cellphone in this house, you have to go the door. – By the way, I don’t have a cellphone. I am one of the few German architects who can live without a cellphone. – The frequencies of devices were tested at home, and we found out that the cordless telephone and the radio alarm emit a strong electric charge. The base of a cordless DECT-telephone always radiates, whether you are on the phone or not. I recommend that you move your workplace and bed at least 6 meters away from the base of the cordless telephone.
So these were the two main characteristics of earth, which were important to me, for healthy living. Then, came the ecological characteristics: that earth, in its production and application, does not alter the environment. It is a local material and it is always reusable.
Earth building techniques are also labour-intensive – which can be good or bad. For the industry, it is obviously too expensive. But in developing countries, it is ideal; it creates jobs.
The earthen bricks in the walls of your home – are they handmade?
No, no. They are factory-made, but not burnt. There is a small factory [not far from here] in Hessen that produces these unburnt bricks 40% cheaper than the burnt ones. The factory has abandoned its ovens, and now focuses on producing these raw bricks.
Dome for living
Germany shows common square houses with two-sided roofs. Nevertheless, your design is inspired by round spaces and dome-shapes. How did you come to this form?
Well, I got my first impression when I was a student traveling through the Balkan and Turkey, and saw the old mosques and the Byzantine churches. They all had octagonal forms with domes, and I was so
fascinated. Then I left it aside, because I thought this architecture is only for religious reasons, and not for a place to live. But later, I happened to stay at the house of Hassan Fatih in Egypt for one night. I slept under an earthen dome, and I said, „Wow! I must try to make one like this!“ And then I designed a house that had a vaulted roof in the middle and four straight walls, but it wasn’t satisfying. It was not a strong design. It took me two years until I found the solution. To live and work under a vaulted roof is fascinating. Since then, I have built almost 40 vaulted buildings!
“I was fascinated: the atmosphere, the energy, the space.”
So once you started to build domes, you stuck to this form, and tried to improve it?
First, I was amazed. By the atmosphere. By the energy of the space. I started to study different traditional building techniques, then I developed new techniques. In concrete, you would need a lot of steel to keep it together, so that it does not collapse.
But here, I have no problem. I can make an opening without encountering any structural difficulty, because I use an optimized cross-sectional cut. It was developed by thinking. Logical thinking.
Did you encounter any problem building domes in Germany? Or round spaces?
I have never had any problem with the shape. Only when we build a dome or a vault with straw bales, we go through a higher workload in the approval process. There is no code or standard. That being said, it is changing now. Last year we built a straw bale project in Northern Germany that includes five vaults. And I am happy that this building has recently been officially certified. I have to admit that I built a lot of experimental things in foreign countries first, in order to gain experience, and that helped me get the authorization to apply this technique in Germany later. The first straw bale vaults we built was in Portugal, and the first straw bale dome in Slovakia.
Does that mean that any architect can build a Dome now in Germany?
You can build a vaulted roof in Germany, of course. You just need an engineer´s calculations.
Which of your buildings is your „baby“? Which one is your favourite?
For a house to live in, it is my home. And for a kindergarten, it is the one in Sorsum, a village near Hanover. It was new and fascinating for everyone. The building has seven domes built out of unburnt earth bricks. And it is completely encased with a green roof.
Enthusiasm for building-it-yourself: is Latin America the new paradise for natural living?
How do you plan the building process? Do you like to work with volunteers for example?
Since I retired, I am mostly active in Latin America, where my knowledge is specially requested for. I hold ten to twelve workshops there a year, plus many presentations on building with earth, building with straw, green roof, and vertical gardens. The workshops mix theory and practice;
there will always be something created on the principle “Learning by doing”. The interest on green and sustainable building is especially big in Latin America, low-tech solutions in particular. Many initiatives have emerged following my workshops and lectures on green roof and vertical gardens. Also, companies have since been established because they supported and realized these concepts. Green roofs have really become a fashion in Latin America nowadays. The Spanish version of my book on green roofs has been re-edited several times already. I built one of the first green roofs in Brazil. Then, a female architect, who had learned from me, continued to build green roofs around Latin America – in Uruguay, Columbia, Brazil and so on. It is really spreading.
And in Germany, do you also teach green roofs?
No, not anymore. When we built the first modern green roof in Kassel in 1978, it was a big hit. Since then, it has become a market possessed by big companies. Very few private individuals build it themselves anymore.
We then carried out the first research on green roof and published the results. On the green roof of my house, for instance, the measurements showed that, when it was +30° Celsius outside, it was a refreshing +17° inside under the green roof. In winter, when it was a freezing -14° outside, it was only 0° under the earth covering. Those results were published in many languages.
But if I wanted to build a house with a green roof in Germany, what would you recommend me to do?
Just do it! Avoid unnecessary expensive solutions. Read my book to avoid some of the common mistakes.
Do I need an architect´s approval?
For any building activities, you need an architect’s approval.
You should think about the substrate, which vegetation could fit together. The orientation and the inclination of the roof play a role too. I give one- or two-day workshops. In one day, you can already learn how to build a green roof!
“For my colleagues in Germany, I was the nuthead, who plays around with mud.”
Why do you prefer to be in South America rather than in Germany?
People in South America are so positive, curious, and interested in learning. You see, here in Germany, people didn’t take me seriously at first. Now I feel accepted, but back then, people said I was „der Spinner“ (German word for: “nuthead” or “crazy”). They said, „You are crazy, playing with mud, old bottles and tyres, and all those stuff … It’s no architecture!“ One day, one of my colleagues went to Japan to attend a conference. They asked him: „Ah! You are from the “Earth Architecture University!“ He didn’t understand. He didn’t know my work. I was more famous overseas than here in Germany. I must have been officially invited to more than 60 international conferences. But most of my colleagues here in Kassel had no idea what I was actually doing.
Did other universities in Germany invite you for lectures?
For lectures, yes, but not many. I have mainly been
invited by international organizations and international universities, and especially by private organizations, alternative groups, ecological settlements or permaculture centers, which are now spreading. There is a large permaculture movement in Latin America, which is much larger than in Europe. The development in Latin America may have started 20 years later than in Germany, but it is so intense!
Building code in Germany – regulates too much?
How did the building code develop in Germany?
Germany had the first earth building regulation in 1947. It was the first norm – worldwide – on building with earth. And then came DIN-norms in the 1970s, but they were withdrawn due to a lack of demand. A few weeks ago, three new DIN-norms for building with earth were established. They involve earthen bricks, earthen mortar and clay plaster. I was a part of the development committee, but I am not happy with what has been decided. The norms regulate too much and expect lots of proof from
the producer of the earth. In my opinion, they limit the development of new products and building methods.
The Dome-shapes were not mentioned in the new DIN-norms, and the earthen bricks that I developed for vaulted roofs, which have been used for my house, and for the kindergarten in Sorsum, and they have soundproof effects that are not within the new DIN standards.
In your opinion, what is the future of building with earth or natural materials in Germany and Europe in general?
Well, it’s coming. Slowly. Building with straw bales, in particular, has become very popular in Europe. I have just received data about new straw bale buildings in Europe. These numbers are derived from a survey that was conducted in 2013. In France, 2500 new houses were built with straw bales in the last couple of years, and 2000 new houses in England, but only 250 in Germany.
Why are there so few new straw bale houses in Germany, compared to France and England?
Are people less interested?
No. It is because of the building regulations. It’s the same in Austria, only 120 new straw bale houses have been built, and in Switzerland only 50 to 60 houses.
In France and in England, the laws seem to be less stringent. Also, there are less regulations in France to build in the countryside.
Is there any association in Germany that can help people build with straw bales?
Yes, FASBA, which stands for „der Fachverband Strohballenbau“ (the German Association of Straw Bale Building). They are currently developing the regulations on building with straw bales.
The mini-budget house
How much would the cheapest 60-square-meter-house with two rooms cost in Germany? What kind of material would you select?
I am not working as architect in Germany anymore. I have not been building any houses here in the last couple of years, so …
If you are going to build it yourself with your friends’ help, I would recommend to build it with straw bales. But you would also need a specialist, who knows what he’s doing and who could accompany you in the building process.
But could you build a house in Germany for less than EUR 100 000?
For sure! A colleague of mine built houses for EUR 1200 to 1500 per square meter, excluding land, but including all the extra costs. 60 square meters would then cost about EUR 90 000.
What kind of machine would you need?
With straw bales, you don’t need any machines. Just good bales and good plaster.
How much time would the building process take from start to finish, from digging to the finished building?
It depends on so many factors. Normally you would start after the frost period is over, in March, and be finished at the end of the year.
Go to workshops! – Nowadays, Universities won’t teach you that.
What would you recommend to students of architecture, who want to build with earth or natural materials? Where could they learn how to do it?
You cannot learn this at universities nowadays. I think the best thing is to go to workshops and take courses or receive training from FASBA, i.e. the European Institution for Earth Building (Europäischen Bildungsstätte für Lehmbau) and the Northern Germany Center for Sustainable Buildings (Norddeutschen Zentrum für Nachhaltiges Bauen).
The intensive courses that we organized at the University of Kassel are now available at the Northern Germany Center for Sustainable Buildings in Verden and are directed by my former assistant, Dittmar Hecken. Those courses are held twice a year and teach techniques such as rammed earth, adobe, clay plaster, repair and even the “earthen-sausage” system.
Interview Prof. Gernot Minke, Kassel, Germany