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Inbetween House by Koji Tsutsui Architect & Associates, Karuizawa, Japan

AR House 2011 Runner Up: in a forest of larch trees, wafer-thin roof planes enfold a cluster of modular structures. Photography by Iwan Baan

An hour from Tokyo by bullet train lies the mountain resort of Karuizawa. On a thickly wooded hillside, architect Koji Tsutsui has built a cluster of cottages that meld and morph together to create a modern refuge in the forest for a couple who work in Tokyo.

Each cottage or module varies slightly in size, according to its function. Five of these modules are grouped together across the site, carefully positioned in response to the topography. A series of triangular connecting roofs bend and fold to enclose the gaps between the modules capturing the irregular, interstitial spaces. These become incorporated into the house as its living room, patios and a sun room. The reciprocity between the different types of space gives the project its name, the Inbetween House.

According to architect Koji Tsutsui, the aim is not to arrive at a final architectural form, but rather to establish a set of design principles relating to the arrangement and siting of the modules, so that the fluid cluster may be expanded and enlarged, should the occupants’ needs change in future.

With a timber structure clad in slim, horizontal strips of larch, the house is beautifully crafted by local builders, using traditional methods of construction. It also exploits efficient and economical methods of environmental control, employing natural ventilation in the summer, with air circulating around the interstitial spaces. In the winter, the temperature can drop to -15˚C, so the house is warmed by a radiant heating system in the concrete floor slab, which heats up at night using cheaper, off-peak electricity.

The jury were beguiled by the subtle and sensitive way in which the house related to its site, and marvelled at how a such a relatively modest building was capable of generating great formal and spatial complexity.

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