The appearance, smell, texture and even sound of wood are all sensations Kengo Kuma wants to convey with his architecture. For Kuma, the architect’s mission is to stimulate, or rather, reawaken our senses, all too often buried under the weight of modern-day concrete boxes. Quality architecture means providing an experience so that “setting foot in a building… is like feeling”, says Kuma. And this he achieves with materials, dialogue with the location, and harmony with nature. Kuma taps into much of the traditional Japanese aesthetic where the relationship between exterior and interior, the built and natural world is paramount.Yusuhara is a small town of about 4,700 inhabitants on the verdant, mountainous island of Shikoku, one of the least populated areas of the Japanese archipelago. The region of Yusuhara is a natural habitat of the Japanese cedar, known as sugi, a tree that can grow as tall as 46 metres. This was Kuma’s material of choice for the town hall, not just as a veneer but also as the basic structural element. He has used it for the 240 sq m
atrium. Four-pillar columns and double, 70x20 cm, laminated beams form a 17.60 m span Vierendeel truss structure. This double pillar and beam configuration gives the construction an overall airiness despite its depth and width. The town hall is in fact one of Japan’s largest public buildings ever to use wood as a structural material and not simply for finishes. Built from the same material that grows on the surrounding hills, the atrium appropriately opens out onto the surrounding landscape. Which makes it the ideal setting for the traditional matsuri festival and other community gatherings. In the snow-bound winters, the atrium becomes a covered public plaza. One side can be completely opened thanks to a series of folding leaves, like aircraft hangar doors, which concertina back to become an integral part of the main façade.
This later, facing south, comprises a series of small cedar wood panels that alternate irregularly with transparent glazed strip windows reflecting the surrounding forest-clad hills. Solid wooden sections alternate with wide transparent areas that reveal the wooden beams inside, giving a three-dimensional character to the façade. A roof overhang protects this façade from direct sunlight. The checkerboard pattern of solid (wood) and transparent (glazed) panels of the other façades is a function of orientation. Panel size and operability are designed to emphasise the user-friendly character of the building, eschewing all monumentality. The double longitudinal and cross beam system on the interior juts out beyond the main façade as if to announce the construction inside. Access to the building is via two protruding box-volumes set on each side of the large atrium. The glazed doorway is placed on the side of each box to maintain the wood-cladding continuum of the frontage. One access leads directly to the atrium and a series of public service counters. The second leads to a staircase and first floor. Here a long corridor with a row of 4-pillar columns runs parallel to the atrium and connects to public service areas behind (a bank, the local agricultural cooperative offices, and chamber of commerce). The second floor is given over to meeting rooms.
Kengo Kuma worked with Professor Shuzo Murakami and Dr Kohei Tsuda from Keio University to ensure the building’s compliance with the strict environmental sustainability regulations, especially with regard to Life Cycle Assessment of Sustainable Buildings. Wood was used wherever possible in compliance, however, with earthquake and fire prevention norms. 750 sq m of cedar wood were used for the outer cladding and 360 sq m to build about 90% of the structural frame. Natural ventilation during hot, humid months is ensured by the large open atrium. Geothermal heat exchange provides heating and cooling during winter and summer respectively.
In summer, 80 kW of electric energy is generated by photovoltaic cells located on the sloping south roof, providing more than 50% of the building’s energy requirement. Given the heavy winter snow falls, particular attention had to be given to ensuring a smooth roof surface that would not trap the snow, as well as to thermal insulation. This later was solved with a boron-imbued 7.5 cm recycled-paper insulation sheet for the walls and a similar sheet with an added plastic resin (polyolefin) layer for the roof. Low-emissivity, 3.40 kW/sq m transmittance, 18 mm double-glazing was installed.
For this project Kengo Kuma received the Energy Performance + Architecture Award in 2007. The building itself is awaiting formal nomination as one of the best CASBEE (Comprehensive Assessment System for Building Environmental Efficiency) buildings in Japan.