A tree-filled courtyard is glimpsed through the shimmering glass-brick facade of this house in Hiroshima, designed by Japanese architect Hiroshi Nakamura (+ movie).
Optical Glass House was constructed beside a busy road, so Hiroshi Nakamura and his studio NAP wanted to create a private oasis where residents could still make out the movements of people and traffic beyond the walls. “The serene soundless scenery of the passing cars and trams imparts richness to life in the house,” said the architect.
This house is sited among tall buildings in downtown Hiroshima, overlooking a street with many passing cars and trams. To obtain privacy and tranquility in these surroundings, we placed a garden and optical glass façade on the street side of the house. The garden is visible from all rooms, and the serene soundless scenery of the passing cars and trams imparts richness to life in the house.
Sunlight from the east, refracting through the glass, creates beautiful light patterns. Rain striking the water-basin skylight manifests water patterns on the entrance floor. Filtered light through the garden trees flickers on the living room floor, and a super lightweight curtain of sputter-coated metal dances in the wind. Although located downtown in a city, the house enables residents to enjoy the changing light and city moods, as the day passes, and live in awareness of the changing seasons.
Optical Glass Façade
A façade of some 6,000 pure-glass blocks (50mm x 235mm x 50mm) was employed. The pure-glass blocks, with their large mass-per-unit area, effectively shut out sound and enable the creation of an open, clearly articulated garden that admits the city scenery. To realize such a façade, glass casting was employed to produce glass of extremely high transparency from borosilicate, the raw material for optical glass. The casting process was exceedingly difficult, for it required both slow cooling to remove residual stress from within the glass, and high dimensional accuracy. Even then, however, the glass retained micro-level surface asperities, but we actively welcomed this effect, for it would produce unexpected optical illusions in the interior space.
So large was the 8.6m x 8.6m façade, it could not stand independently if constructed by laying rows of glass blocks a mere 50mm deep. We therefore punctured the glass blocks with holes and strung them on 75 stainless steel bolts suspended from the beam above the façade. Such a structure would be vulnerable to lateral stress, however, so along with the glass blocks, we also strung on stainless steel flat bars (40mm x 4mm) at 10 centimeter intervals. The flat bar is seated within the 50mm-thick glass block to render it invisible, and thus a uniform 6mm sealing joint between the glass blocks was achieved. The result – a transparent façade when seen from either the garden or the street. The façade appears like a waterfall flowing downward, scattering light and filling the air with freshness.
The glass block façade weighs around 13 tons. The supporting beam, if constructed of concrete, would therefore be of massive size. Employing steel frame reinforced concrete, we pre-tensioned the steel beam and gave it an upward camber. Then, after giving it the load of the façade, we cast concrete around the beam and, in this way, minimized its size.
The garden is raised up to first floor level to make room for a garage below and the architects used 6,000 specially made glass blocks to build a two-storey-high wall in front of it. The wall was too tall to support itself, so the blocks had to be bolted together.
As light filters through the glass it creates dancing patterns across the walls and over a group of maple, ash and holly trees.
“The facade appears like a waterfall flowing downward, scattering light and filling the air with freshness,” said the architect.
An open living room is located just behind and is only separated from the garden by a lightweight metal curtain. This curtain folds back to reveal a second glass-block wall at the back of the room, which lines the edge of a central staircase.
Residents are faced with the staircase upon first entering the house. A water basin skylight is positioned immediately above and projects more light patterns onto the floor.
A split-level second garden is located at the back of the house, while the children’s rooms occupy the top floor, a dining room and kitchen are on the first floor and a hobby room, Japanese room and extra bedroom can be found on the ground floor.
Hiroshi Nakamura worked under Kengo Kuma before setting up his studio in 2002. Previous projects include the Roku Museum, a small art gallery with softly curving walls.
Project name: Optical Glass House
Main purpose: Housing
Design: Hiroshi Nakamura & NAP Co.,Ltd.
Structure design: Yasushi Moribe
Contractor: Imai Corporation
Location: Naka-ku, Hiroshima-shi, Hitroshima, Japan
Site area: 243.73m2
Total Floor area: 363.51m2
Completion year: October,2012