Area context
The building is located in one of downtown Tokyo’s most attractive areas, surrounded by fashionable boutiques and exclusive restaurants. The footprint of 388-square-foot buildable area on a 646-square-foot lot is incredibly small; however this is not unusual to build on such a small site in Tokyo, where demand for property and real estate values are very high. The city has no minimum buildable lot size restrictions but shadow and setback regulations limit the size of the building envelope.
On such a small site, it is crucial to maximise the potential of every space so Sejima adopted the strategy of calculating the permissible building envelope and then designed from the outside in.
From the outset, Sejima thought the building should be a unique-looking response to its extreme site conditions. The shape, she maintains, resulted from the requirements of the slabs and walls so function dictates the form here.
The spaces created on such a site are unavoidably small, facilitating the minimum necessities of daily life. However when considered in context this house is successful because many people in Tokyo live in confined spaces which creates a need for urban resources to expand the occupant’s available space. The result is a culture that uses parks instead of back gardens and cafes instead of living rooms - which suits this house perfectly.
Structure and staircase
The main element of this house is the spiral staircase that connects the four floors. The design of this staircase is very open which creates a sense of freedom and encourages sociological behaviour in the inhabitants. The openness of the staircase also helps create subdivisions between the floors, which induces a sense that there is more space in the building and eliminates the feeling of being trapped within a confined space.
The square enclosure for the staircase is the core structure, made from vertical and diagonal steel bars it acts as a column to counter horizontal shear and earthquake forces. The outer skin of galvanised steel and glass is supported by a web of steel with elements no more than two inches in diameter. The vertical parts of the steel webbing wrap around the building like flow lines that respond to the changing dynamics between floors.
The concrete floors partially cantilever off the staircase enclosure and connect the interior and exterior steel work. As a result of the ever changing dimensions between central staircase and exterior wall, the building adopts a sense of weightlessness that is accentuated by the glass walls. The powerful sculptural presence of the staircase varies constantly as the occupant moves through the building according to the outside wall’s proximity, shape and transparency.
Arrangement of spaces related to family needs
The house was designed to function as a family home and due to the space limitations; each floor was only given one or two uses. Segima says that she “felt uncomfortable dividing up already small spaces” and as such, she uses the spiral staircase to separate rooms instead of walls.
The dimensions and shifting of the four floors was carefully considered in relation to the parameters of the site and the client and to best accommodate each floor’s functional requirement. The floors were also arranged to achieve hierarchy:
Basement: Parent’s bedroom and lavatory with shower. So as not to waste space on an unnecessarily large bedroom, the space was split to allow for a sunken patio as well.
First Floor: main entrance and daughter’s future room. This floor was deliberately kept small to allow for an off-street parking lot – a must for Tokyo car owners.
Second Floor: Prime gathering area for cooking, living and dining. The ceiling soars to 11-foot-high, befitting its importance as the prime gathering place. “Every other slab is smaller and cannot project beyond this one” Segima explains. Room was needed on this floor to fit a galley kitchen so the slab was pushed out towards the property line.
Third Floor: a bathroom with a deep soaking tub and city views shares the third floor with a covered terrace.
Each floor defines different-sized open spaces around the fixed vertical element of the staircase. The floors align with exterior spaces to create an almost perfect use of space arranged in a sort of three dimensional jigsaw.
Privacy, light and views
The tilting, faceted outside walls change the quality of light and view for each room. With angled surfaces of standing-seam galvanized steel and clear or translucent glass panels, each face was carefully orchestrated to maximize the connection to the outdoors without compromising privacy. To achieve this balance, Sejima punctured the opaque walls with openings carefully positioned to control views in and out. She also cut clear areas within the glazing's translucent film and provided square, hinged windows, just big enough to let in fresh air.
Glass wraps both corners but aptly turns translucent where the building greets the street. Through the clear zones, distant views of the Shinjuku business district's skyscrapers make the interior seem bigger.
The form is truly unique, somewhat dictated by the required function but still featuring unusual geometry. The desired effect if for the occupants to feel liberated through a series of connecting spaces that relate to and accommodate for the exterior arrangements.
