Sustainable Buildings based on international know-how exchange and adaptation – technological approaches on building physical problems of building envelopes in terms of climate difference

While the need to reduce energy consumption in buildings is well accepted, the exact measures to be taken to counter the resulting emissions are generally not agreed on. The general discussion is whether to focus on passive (the envelope), active measures (heating/ cooling system and the energy generation) or user behaviour to reduce energy consumption. This gets even more difficult when building concepts are to be transferred and adapted to other climates than where they originate from. As the demand in many countries for knowledge on how to most effectively reduce the emissions from the building stock is high, the need for a sound approach on this problem is likewise huge.The poster will introduce an ongoing cooperation between the University of Tokyo and ETH Z\ufcrich on developing sustainable buildings for Japan, using existing know-how, technology and experience values from Switzerland and/or Europe and tailoring them to Japanese culture and climate. In Japan, the low energy efficiency and the short life-span of buildings are the outstanding issues. Their poor insulation and ventilation plan are requiring huge energy consumption for heating and cooling. Furthermore, countermeasures against heat and moisture problems are so insufficient that dew condensation would cause mold growth resulting in biological deterioration of building elements and emission of poisonous substances. The main reason is that generally only several standardized construction methods are employed regardless of wide range of design conditions and engineers are lacking sound building physical knowledge.In this study, a flexible and sustainable building envelope whose wall make-up can be tailored easily to local climate and use behavior was developed. For social and ecological sustainability, this method allows the building elements to be free from condensation ensuring the longevity of buildings, inhabitants’ health and the energy efficiency because of the sufficient amount of insulation and its systematic ventilation. At the same time, the materials used as building components consist of wood and soil that have low environmental load for production and don’t contain toxic compounds. For economical sustainability, the well-organized insulation and ventilation system keep the running consumption low. As a unique potential steaming from the construction method, it can offer the industry to utilize a large amount of small-sized woods which come from forest improvement and are regarded as too weak to use as structural elements.For validating the feasibility of this building envelope, the hygrothermal property of the wall was examined. From the view point of building physics, the main problem concerning Japanese climate is high level of humidity in combination with high temperature in summer. Thus the moisture sorption characteristic of the wall is hereby of prime concern. For archiving a quality simulation, the individual materials’ hygrothermal properties were tested as well as full scale test walls using standard conditions. In parallel, transient heat and moisture simulation was also done. As a result, the simulation and the experiment corresponded each other with high accuracy. Consequently, it was shown that the envelope can eliminate the risk of dew condensation in comparison with conventional wall constructions