A cluster of boxes united by irregular, interstitial space, InBetween House mimics the Japanese urban condition on an architectural scale. While the rectangular volumes are like small buildings, the amorphous areas in between are akin to the narrow passageways and odd gaps that crop up almost organically in Japanese cities. A bit of an anomaly, this house is a full-time residence located in Karuizawa, a tony vacation town 95 miles northwest of Tokyo. Yet for the owners, a 40-something couple with jobs in the city, the daily commute by bullet train is a small price to pay for waking up in the country.

The relatively recent introduction of this high-speed train route made the clients' lifestyle logistically possible; it was the economic downturn, however, that made it a reality, since they were able to get a good deal on the 16,000-square-foot property. Situated within a planned second-home development not far from the station, the secluded parcel marks the end of a narrow, winding access road. Though neighboring houses are visible, the plot abuts a protected forest owned by Japan's imperial family. In the hope of attracting a buyer, the developer cut a level strip of land across the steeply sloped, square parcel thirty years ago but was hesitant to unload it until recent financial woes forced his hand.

Thanks to the developer's regrading, the site was basically construction-ready when the clients took possession. Inspired by the soaring karamatsu pine trees and the alpine scenery, they imagined their new house as a blend of Philip Johnson and Junzo Yoshimura. 'It was kind of a contradiction,' says architect Koji Tsutsui. 'They wanted slanted roofs and they wanted large glass windows.'

A city slicker who divides his time between practices in San Francisco and Tokyo, Tsutsui worked for Tadao Ando in Osaka for six years before hanging out his shingle and building rectilinear, concrete homes independently. 'This situation required me to design in a freer way,' says Tsutsui of InBetween House. Inspired by his own scheme for a Ugandan school and orphanage (2008), for which he created eight modular huts interconnected and shaded by sloping roofs, InBetween House marks a continuation of this dynamic new direction for Tsutsui.

The architect's initial design featured a linear string of rooms topped with roofs that pitch in different directions. But after splitting the volume into discrete boxes and moving them around like chess pieces, he realized that manipulating the interstitial space was the key to enlivening the plan. Many computer-generated iterations followed until the architect and the clients agreed on a loose circular configuration defined by five boxes, glass walls, and a continuous but multifaceted roof.

Moving clockwise from the driveway, the boxes house the garage, the combined kitchen and dining room, the master bedroom, the bathroom suite, and two stacked guest rooms ' one Western style and one tatami ' that occupy the only two-story volume. The resulting infill doubles as the home's circulation system and segues smoothly from one end of the house to the other, starting as an outdoor terrace wedged between the garage and kitchen, then morphing into a second terrace centered on the front door. Inside, the space fans out to become the living room, followed by the 'sun hall' and the sunroom, a sequestered sitting area overlooking the tree-studded hillside. 'The plan may look random, but even a slight shift would change everything,' explains Tsutsui.

Precisely positioned at 30 or 60 degrees apart, all of the rectangular rooms relate to each other geometrically. Measuring roughly 11 feet by 21 feet apiece, they are also close in size and proportion ' like the rooms in a traditional Japanese house. The self-contained boxes clad with local pine on the outside and white gypsum board on the inside hold mostly private places. By contrast, the free-flowing void seems barely enclosed by full-height insulated, double-glazed window walls that blur the boundary between inside and out.

Overhead, the entire house is covered with a 1-inch-thick steel roof composed of sloped planes that slant in multiple directions and at different angles. While the overall strategy complies with the local building code's pitched roof requirement, the specific dips and drops facilitate drainage and respond to internal ceiling considerations. Ranging in height from 6 feet just outside the kitchen to 17 feet above the guest room box, the roof sections accommodate the comfort, climate, and functional needs of the individual rooms. Low ceilings provide a intimate atmosphere in the private quarters, and high ceilings open the living room and sun hall to expansive views of the countryside.

Unsurprisingly, the roof structure was the contractor's greatest challenge. Tackling the easiest step first, he topped each timber-framed box with straightforward beams and joists. They terminate in overhangs that touch the adjacent eaves at discrete points, loosely joining the boxes in a closed ring. Trimmed to fit, additional wood members span the voids, uniting the individual roof sections like a crazy quilt.

Above that, a steel layer consists of five simple rectangles that top the boxes and eight triangles to fill in the gaps. Because the boxes vary in height, slope, and orientation, many of these inserts twist or slant in two directions. To alleviate a complex convergence above the sun hall ' the only spot where three boxes meet ' the architect installed a skylight. This solution infuses an otherwise shadowy circulation node with soft daylight.

Forming the exposed ceiling inside, the roof's chaotic framing system terminates outside in orderly wood bars inspired by traditional taruki, or rafters. Ringing the roof perimeter, they support deep eaves of 2 feet or more that provide the only sunshade. Due to the slanting roofs, the glass walls slope, making curtains or blinds difficult to hang.

Fortunately, Karuizawa summers are mild, and natural ventilation, enabled by well-placed operable windows, cools the interior. In the winter, when temperatures often plummet to minus-5 degrees Fahrenheit, electric radiant heat panels directly below the concrete floor warm the entire house. Boosting the insulation that blankets the walls and roof, these electric panels warm the soil beneath the house at night, benefiting from the earth's ability to retain heat and from Japan's lower electricity costs during off-peak hours. By day, when the utility price is higher and the owners go to work, the system shuts off. But the rising heat (abetted by a wood-burning stove in the living room when needed) maintains constant, comfortable temperatures throughout the house.

At ease with Karuizawa's climate and topography, Tsutsui's InBetween House takes advantage of its country setting without compromising the comforts of a city dwelling. Its boxy rooms may bow politely to Ando, but the flow of connecting spaces has an urban order that forms a quirky shape uniquely its own.

Naomi R. Pollock is RECORD ’s Tokyo correspondent and the coauthor of New Architecture in Japan (Merrell, 2010).

Gross square footage: 1,818 sq. ft.

Completion date: October 2010

Architect:
Koji Tsutsui Architect & Associates
Japan: 3-28-10-304 Kyodo Setagaya-ku, Tokyo
U.S.:  1090 Francisco Street, #7
San Francisco, CA 94109
info@kt-aa.com