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Canopy at Hoshakuji Station by Kengo Kuma and Associates, Takanezawa-Machi, Toghigi, Japan

Kengo Kuma creates a varied spatial experience by applying a diamond plywood motif to an otherwise steel station bridge. Photography by Edmund Sumner

Last month, Japanese architect Kengo Kuma was one of seven recipients of a RIBA 2009 International Fellowship. In the award citation, jury members noted how Kuma’s buildings ‘have an extremely tactile character, which invariably harmonises with the topography in which they are situated, irrespective of whether they are in the country […] or in the city.’

Maintaining his skilful inventiveness, this project creates one of his most striking topographies to date. When discussing its making with the Architectural Review, Kuma explains how the notion of tactility also endures throughout his design and construction process. Hoshakuji Station is situated in Takanezawa-machi, in the Tochigi Prefecture, 80 miles north of Tokyo. Adjacent to Kuma’s Chokkura Plaza - a public space and pavilion with a hybrid steel and Oya stone structure articulated in shallow, vertically stacked diamonds - Kuma reapplied the diamond motif to the soffit of this new structure. He did this in order to bring distinctiveness to a potentially anonymous station bridge.

In his opinion, recent standardisation has produced too many bland, unresponsive structures, meaning stations are ‘unable to reflect the character of the areas they serve’. When analysing a simple diagonally braced steel structure, Kuma was inspired to develop a timber soffit, suspended on steel hangers, which would change in profile to create a varied spatial experience.

On the upper concourse the ceiling depth is at its most shallow, creating a generous lofty space, while toward the edges and at the base of the stairs the ceiling drops to create enclosure and foil the deepest structural members.

There are approximately 1,500 diamonds in total, that in plan share the same size and proportion, with cross-axial dimensions from point to point of 900-1,820mm. The complex topography is then created by varying the shape of each suspended panel, cut in a straight line on an angle. When joined in diamond, a continuous but irregular profile is created that establishes four corner coordinates coincident with adjacent units. Having digitally mapped the precise contours of these timber stalactites, a grid of coordinates was plotted that varies between 100mm and 1,700mm deep.

Kuma then checked the depth of each unit and adjusted it through the process of model-making, perspective-rendering, full-size mock-ups, and finally during construction.

‘I don’t fully trust the computer so I always test detail with a real-size mock-up and with the real material,’ he says. With a reflected ceiling plan indicating cutting depths, each panel was pre-cut off site.

The diamonds were then assembled on the ground before being hung one by one. Reassuringly, in the practice’s own words, ‘since it is a station building used by many people, we paid extra attention to prevent fall-down of the plywood, with each diamond bolted in four parts to the steel beams supporting the roof’!

In his acceptance speech for the RIBA International Fellowship, Kuma credited the recession that paralysed the Japanese economy in the 1990s as the stimulus for his ‘return to material’, forcing him to work directly with craftsmen. Since then his work has been inspirational, demonstrating the expediency of craft over mechanisation and how to achieve maximum effect from minimum means.

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