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Making waves: Bath House in Gunma by Kubo Tsushima

AR_EA 2016 Finalist: Bringing an ancient tradition into the modern world

As the hotel Maruhon Ryokan saw its guest numbers decreasing, its owners commissioned architects Hideaki Kubo and Yumi Tsushima to design a new bath house. Throughout the Japanese institution’s 400-year history it has witnessed several transformations; this time the aim was to rejuvenate its image, promoting the hot springs at Sawatari as an enviable sustainable tourism destination. Soak in hot spring waters; explore the mountainous surroundings of the Gunma prefecture.

With Kubo Tsushima Architects’ addition, completed in 2015, the hotel now offers a ‘modern designer’s bath with a double-height structure and beautiful curved ceiling’ sitting between two of its accommodation wings. From the street, the new volume appears to follow a traditional Japanese style in terms of proportions and the gabled roof. While the timber ensures it stands out, it is the inside that truly sets this project apart.

Bath house site plan by Kubo Tsashima

Bath house site plan by Kubo Tsashima

Bath house plans by Kubo tsashima

Bath house plans by Kubo tsashima

Bath house plans by Kubo tsashima

One gesture is all it takes: one line, in section. A Japanese cedar curved slab splits the volume, creating a generous space below and, above, an inclined wall against which to rest. On the ground floor is the bathing room: healing waters from Sawatari hot springs flow from a black bamboo tap into a small sunken pool while light pours in from above – computational fluid dynamics have been used to create buoyancy-driven ventilation. On the upper level sits a resting room, housing a bench of Japanese cypress, chosen for its aroma and the feeling of relaxation it affords. ‘We carefully design the details to make exceptional spaces,’ explain the architects, who aim for a ‘rational, intelligent and economical way to make architecture’.

Inclined planes feature in other projects of theirs, reminiscent of Claude Parent’s oblique world. In Rooftop Community, the houses’ roof slopes extend out, linking dwellings to one another while forming slanting floors for dining and sunbathing – a new spatial continuity, as Parent suggested, could offer new social opportunities. Sloping planes were never really considered practical but, in Maruhon Ryokan’s bath house, the inclusion helps to create a unique immersive experience for the guests.

Bath house section by Kubo Tsashima

Bath house section by Kubo Tsashima

Bath house section by Kubo tsashima

Bath House

Architect: Kubo Tsushima Architects
Structural engineer: Megumi Tamura, TIS & Partners
Photographs: Koji Fujii, Nacasa & Partners