This is what climate protection looks like

High energy efficiency, lower costs

Bio-Solar-House: energy-awareness and healthy living

Energy consumption is both an environmental and a financial issue. Since mid-2008, the law has required that documentation be provided on the energy consumption of buildings that are rented, sold, or leased. Moreover, the new Energy Saving Ordinance (the EnEV) came into force on October 1, 2009. It requires the owners of new or renovated buildings, to lower their energy demand for heating and warm water by roughly 30 percent compared to previous guidelines. This makes sense, as oil and gas prices keep rising. This is not only good for the environment; it is also easy on the homeowner’s wallet in the long run. As a result, low-energy homes have been very popular for some years now. The “passive house” has become one of the most well-known kinds, as such houses are particularly energy-efficient. Yet passive houses also have disadvantages: They often have problems and hidden health hazards. A new building concept, however, offers an alternative to passive systems: the Bio-Solar-House. It exploits the power of the sun and relies on natural building materials and PLEXIGLAS® to create a comfortable home environment.

The concept of a passive house is actually quite straightforward. To save heating energy, it prevents as little heat as possible from escaping. This is why the buildings are superinsulated, with barely any thermal bridges through which energy can escape. Because of their air and water-tight design, they resemble a plastic bag in the way they work. The problem here is that an average household produces up to seven liters of water vapor every day, through cooking, showers, laundry, and the people who live in them. In order for the vapor to escape naturally, the house has to have walls through which water vapor can permeate. In the technical jargon, they are said to be “open to vapor diffusion.” By the same measure, passive houses also need to be completely air-tight if they are to retain heat. This complicates passive house design: Ventilation and filtering systems are needed to channel the water vapor outside. Without an artificial ventilation system, the water vapor would otherwise condense on the inside surface of the walls, resulting in moisture levels that could damage the building and in mildew, which is harmful to health. Udo Guenther-Dreisbusch, an architect, knows this problem only too well. As a building surveyor for, he checks passive houses on a daily basis for construction defects. “When I remove insulation boards, the wall behind them is often completely covered with mold,” he tells us. House dust mites thrive especially well in the damp climate, too, and their droppings trigger a variety of allergies in humans.


The ventilation systems of passive houses have to work perfectly at all times if such damp conditions are to be avoided. In addition to the cost of electricity for these systems, these houses frequently run up high costs for maintenance. Klaus Becher, a mechanical engineer, knows from his job as a technical manager for industrial plants how fraught with problems the technology can be. The 74-year-old therefore decided to design a low-energy house that requires little, if any, technology and saves energy and protects the health of its inhabitants and the environment. He used various resources to gain the knowledge he needed to build the first Bio-Solar-House. “We engineers have a disease: We’re always asking, ‘Why?’” he explains with a smile on his face. “This curiosity and the knowledge of physics that anyone in my line of work should have, a range of books and my professional experience formed the foundation for the design.”

Perfect enclosure

A variety of components are combined in Becher’s Bio-Solar-House, which has since been patented. The heat insulation is not based on an air-tight design, unlike that of a passive house. The Bio-Solar-House works on the “house-in-house” principle: A weather-proof exterior shell surrounds the vapor-permeable interior walls, which are covered by a layer of cellulose, a natural insulation material. There is an air space between the exterior shell and the interior wall. This air space insulates the living spaces very effectively, as it is heated through a naturally occurring physical phenomenon, the greenhouse effect. Through transparent surfaces in the facade, roof, and garden room, the sun heats the air space, just like a greenhouse. For this, it is important that a maximum amount of warming sunlight enters the structure. Light-transmitting multi-skin sheets are therefore an important part of the energy concept. PLEXIGLAS ALLTOP® multi-skin sheets meet these requirements perfectly since they transmit up to 91 percent of sunlight. “We use PLEXIGLAS® because it offers exceptional light transmission and is also resistant to weathering and UV-light. Unlike other plastics, that means it shows no yellowing, even after decades,” says Becher. In fact, the manufacturer provides a 30-year guarantee on this. Since the double-skin sheets also have good inherent heat insulation properties, they prevent unnecessary heat loss to the outside. Their low weight means few supports are required even for the large glazed surfaces in the conservatory, giving it a light and airy look.

Fire and water

The air space between the exterior shell and the interior wall protects the interior of the house from heat loss. For the interior to warm up in the first place, the Bio-Solar-House uses a solar-thermal unit. This is located in the roof underneath a light strip made of transparent PLEXIGLAS®. The sun’s rays heat the water in the unit’s black pipes. The water is used as process water and for heating the walls. In the transitional periods of spring and fall, the sun’s energy is enough to keep the inside of the house comfortably warm. Only in the winter does the house need to be heated by a wood-burning stove. According to Becher, the Bio-Solar-House consumes 10 to 25 kWh of heating energy per year per square meter of useable space, while the primary energy consumption is less than 10 kWh per square meter. “These figures are lower than those for a passive house and correspond to annual heating costs of 150 to 350 euros,” Becher claims. By comparison, a newly built apartment building consumes about 100 kWh of heating energy annually per square meter of useable space.

The Jacobi family has been living in a Bio-Solar-House since 2005. They use their stove from November to March. “If the temperature is around 5 degrees, all we have to do is fire up the stove for two hours every two days. If the temperatures are below zero, we heat for two hours every day,” says father Darko Jacobi. In 2008, this required four cubic meters of wood. “It was cheap—only 50 euros. The only other additional costs for our house were the 630 euros for our 3700 kW/h residential electricity.”

Dust-free heat

Bio-Solar-Houses are therefore even more cost-effective in their energy consumption than passive houses. Passive houses also come with the additional cost of filter maintenance for the ventilation system. The filters are supposed to clean the outside air of air pollutants, pollen, and dust. The filters themselves need to be cleaned regularly to prevent bacteria and viruses from multiplying. That is a lot of effort just to be able to live healthily.
On the other hand, the vapor-permeable walls in a Bio-Solar-House sustain a healthy living environment. Unpleasant odors and water vapor can escape through them. The natural circulation of air means that no air filters are necessary—and thus no threat of harmful bacteria. The wall heating is another bonus for healthy living in the Bio-Solar-House: It does not stir up dust, which makes life easier for people who suffer from allergies, asthma, rheumatism, and neurodermatitis.

In summer, the house-in-house design also provides the necessary cool temperatures. When the outer doors of the garden room are opened, the warm air is simply drawn under the roof to the top, in what is called the “chimney effect.” Ventilation hatches located in the roof allow the heat to escape. “This keeps the inside of the house pleasantly cool when the weather is hot, without the need for all kinds of ventilation technology,” Becher explains.

In tune with the times

Following on from his personal project, Becher then founded a company: the Bio-Solar-Haus Becher GmbH. It builds detached houses and apartment buildings, with one or two stories as desired. “We’ve also built functional buildings such as kindergartens, schools, office buildings, and spas using this design.” explains Hubert Becher, the managing director and nephew of the developer. The numerous awards that Klaus Becher’s house design has earned attest to the fact that it meets the requirements of energy-conscious and healthy living. They include the energy seal from the EffizienzOffensive Rheinland-Pfalz, the innovation award from the federal state of Rhineland-Palatinate, the Gesundes Haus (“Healthy House”) the Eco-Construction Award from the IDUNA home loan bank for German craft trades and the World Energy Globe Earth from the European Parliament.

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