Ellipse Sky

Labor of Love: Two young designers deliver a refined and spirited concrete structure to a client looking for a unique family home and rental complex.

Soft concrete may be an oxymoron, but Ellipse Sky, a four-story residential building designed for an obstetrician, his family, and several tenants, deftly pokes holes in that notion. 

A concrete box on the western edge of Tokyo, the house is the first freestanding structure by Keiko + Manabu, a young design duo specializing in commercial interiors. 

The pair teamed with engineer Akira Suzuki to craft a building that mollifies the hard material with swooping arches, graceful details, and walls as smooth as a baby's bottom.

The decision to build with concrete was a given from the start when the client purchased a plot near his birthing center and invited three firms—all with female principals—to participate in a design competition. Approaching the brief with the vision and sensitivity of interior designers, partners Keiko Uchiyama and Manabu Sawase presented a large-scale (1:20), easy-to-understand model and landed the commission. “This is a very important scale for us,” says Uchiyama. “It is where you can imagine the inside from the outside.”

Connected by an exterior concrete stair and elevator, the building consists of a duplex apartment on the top two floors for the doctor, his wife, and their two children (both medical students), independent quarters for his mother on the second floor, and six duplex rental units accessed directly from a garden walk at grade. But the project took three years to complete, partly because of the laborious construction process needed for the concrete's carefully conceived forms.

Wanting to offset the rigidity of the cubic building, the design team devised a facade punctuated by a series of apertures: large ones that maximize unimpeded sky views from within, and small ones that edit out the neighborhood dominated by small-scale apartment buildings and single-family homes. A tall, narrow arch framing the elegant spiral stair marks the entrance to the family quarters. 

“We wanted many openings, so the wall had to be as thin as possible,” notes Uchiyama. Affixed to the building for stability, but essentially self-supporting, the facade measures a mere 9 inches thick at the edge of the arches.

Because of their shape, the wall's convex curves could not be completed with straightforward pours, requiring vibration to coax the concrete under inverted crowns. Yet this was child's play compared with the complex 3-D formwork used for the curvaceous stair, with its subtle oval plan and concave undersides, and the varying ceiling heights at every level.

This dynamic element spirals up to the doctor's home, a 2,960-square-foot duplex entered on the third floor. Here an L-shaped terrace mitigates the site's irregular geometry, while shielding the interior from direct sunlight with a cantilevered roof 20 feet above. Inside, a foyer leads to a reception room and the family's open living/dining room and kitchen, framed by full-height, arched windows facing the terrace. A bathroom, workroom, and master bedroom are tucked behind these public areas. 

Internal stairs connect to the children's rooms and a second bath above. Compact by comparison, each 431-square-foot rental unit features a multipurpose space on the ground level and sleeping quarters above—perfect for a couple with a baby.

Uchiyama and Sawase carefully considered wall surfaces and details. “In the United States, fun finishes are common, but because Japanese houses are smaller and people rarely entertain at home, they get less attention,” Uchiyama explains. They used patterned wallpaper and decorative paint to add homey touches to the rentals, and drew from their usual palette of commercial materials—tile, terrazzo, and slatted window blinds—to complement the concrete surfaces within the doctor's home.

In the end, the concrete itself showcases the designers' talents most effectively. Treating the interior with the same finesse as the building's large architectural gestures, they created velvety concrete walls by coating the formwork with urethane. Then they softened harsh, rectilinear wall openings and corners by refining them with playful cutouts.

Thanks to exacting design standards and highly skilled contractors, legions of Japanese architects have been achieving remarkable results with concrete since before Uchiyama and Sawase were born. But few have fundamentally changed its character and expression. By placing as much value on the detailing inside Ellipse Sky as on the wow factor of the building's external form, Keiko + Manabu has mastered the tough material's tender side.

Completion Date: August 2012

Size: 7,677 square feet

Cost: withheld

Architect:
Keiko + Manabu — Keiko Uchiyama, Manabu Sawase, design principals