Mud house, straw insulation .. Co. – Green houses are still the exception
- Building with natural materials like straw, clay or earth is rather rare nowadays.
- Such building materials are not only climate-friendly, but sometimes even cheaper.
- But there are some peculiarities of the natural materials to consider when planning.
Gunzburg. Living like a hobbit has its advantages. Robert Sengotta can celebrate his salsa parties – and the neighbors still have their peace and quiet. Tons of earth and concrete and triple-glazed windows make sure of that. "The sound insulation is exceptionally good", says the software developer about his earth house in Gunzburg (Bavaria). Virtually nothing leaks out or in.
Sengotta’s own home is somewhat reminiscent of the caves that Frodo and his friends found in the epic "Lord of the Rings" inhabit. It is a mound of earth with a large window front facing south. This orientation ensures a brightness that is anything but typical of caves. "That it is dark here is a widespread prejudice", assures Sengotta. On the contrary, "above-average light be it.
At some point, the construction method was no longer considered sexy, but today people are returning to it.
Klaus-Jurgen Edelhauser, civil engineer
Earth houses are a rarity in Germany – even Sengotta describes them as "exotic", which does not necessarily have anything to do with their intrinsic values, but rather with the ideas of what a house should look like. Living under a mound of earth is not exactly what many people think of as a modern residential building.
Back to the origins
Yet this is a very old construction method, says civil engineer Klaus-Jurgen Edelhauser from Rothenburg ob der Tauber, Germany. It goes back to the very original behavior of humans to seek shelter in caves. "At some point, the construction method was no longer considered sexy, but today people are finding their way back to it."
This concerns not only earth houses, which actually represent rather a small niche, but also clay and electricity as basic building material. "They were commonplace in medieval buildings", says Edelhauser and adds: "In recent years, they are experiencing a renaissance – and are becoming increasingly popular."
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The Agency for Renewable Resources (FNR) also uses the Renaissance term. The FNR, established in the 1990s on the initiative of the German federal government, oversees research projects on all aspects of renewable raw materials. Around a "revolution but it is not a question of that, but of "slow, steady rethinking".
Figures such as those from the Straw Bale Construction Association provide an example of how there is still room for improvement: The association estimates the number of straw-insulated buildings in Germany at 900 to 1500. By way of comparison: the stock of residential buildings is around 19 million.
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Climate debate as a catalyst
The debate about climate protection has brought traditional building methods using loam, straw or earth back into focus, and with them the greatest possible use of conventional building materials. The natural building materials are particularly climate-friendly in their production and disposal, explains Edelhauser, who sits on the board of the Bavarian Chamber of Civil Engineers. In addition, they would be produced without high energy expenditure.
Naturally grown materials such as straw or even insulating materials made of wood or jute also have a so-called CO2 sink effect. During growth, plants split carbon dioxide into oxygen and carbon – they release the oxygen and bind the carbon. This also remains bound as long as the building stands, explains Anna Wolff of Deutsche Umwelthilfe (German Environmental Aid).
Benefits and challenges
But the good conscience of having done something for the climate alone is unlikely to convince most builders. However, alternative building materials also have certain practical advantages. Clay, for example: "It contributes to a pleasant indoor climate because it has excellent moisture buffering properties," says the software developer about his earth, describes civil engineer Edelhauser.
On the other hand, the materials have certain vulnerabilities that planners have to take into account. With straw and clay, for example, moisture protection is important, says Edelhauser. "Straw gets moldy when it gets wet and can’t dry anymore. Clay, on the other hand, swells when exposed to massive moisture." Basically, however, this can be prevented through construction.
Concrete is still needed for the foundation
In general, however, natural materials reach their limits in moisture-critical areas, such as foundations. "There is still a lack of innovation", says Rene Gornhardt, building materials expert at the FNR. Alternatives, for example a textile concrete with flax as reinforcement, are not yet mature enough to be used promptly in single-family home construction.
This means that the foundation can hardly be built without concrete. "And we know that it is not exactly ecological material", says Gornhardt. It is possible to use a strip foundation with less concrete as a base or to plan a house without a base plate at all. This is technically quite possible, but rarely implemented.