The rigid horizontal diaphragm formed with steel beams (partly wood) is set on conventional wooden frame walls, and glulam rafters (240×54mm) are arranged at 500mm intervals making 9m span wooden roof. On top of that, secondary rafters making long eaves are set for in-roof ventilation and radiation heat barrier as this house locates in an area with strong sunlight. [Learning from traditional knowledge] Traditional building techniques were referred, as a crystal of sustainable design. In a Japanese traditional house, main rooms (e.g. living room) were surrounded by non-living spaces such as veranda and attic.

These non-living spaces worked as not only a passage and storage but also a buffer space (air space) in between the outside and living spaces. For instance, a veranda was used to regulate a connection between the outside and inside by opening and closing its fittings in accordance with seasons and time as environmental adjustment system. This would be the wisdom cultivated before modern era when no mechanical HVAC system exist. Like this example, traditional knowledges were combined with modern technologies to develop new ways of sustainable design in this project, as summarized below. "Air insulation" Learning from the traditional technique, it was aimed to stabilize thermal environment of the living spaces by surrounding it with non-living spaces regarded as the air space.

Based on a computer simulation, the building composition was decided: 1) surround three sides of the living space by the air spaces, 2) insulate the north wall and roof, and 3) make ceiling height assuring air space above. Thermal condition of the living space was measured in the house and it was confirmed that the temperature of living space was maintained about 10 degree Celsius higher than the outdoor temperature without heating in winter. "Traditional wood processing" Yakisugi, a carbonized cedar board, is the Japanese traditional technique to enhance material properties of wood.

A surface of cedar board is burnt to make about 5mm thick char layer to improve durability, weather resistance and fire resistance. We made Yakisugi with client and used it for the exterior cladding. Yakisugi is basically maintenance-free. "Material reuse" Kagoshima is famous at stone building culture. However, recently, old stone buildings have been demolished and dismantled stones are disposed. To inherit the tradition, local granite used in an old stone warehouse was used for the exterior floor. Photo Credit: Shigeo Ogawa, Tomonari Shimasaki, Atsushi Takano