Mimicking the shapes of the surrounding hills, floors sloping up to strategically located windows let light into a basement room and two other levels of this Japanese home while directing views upward beyond the neighboring structures. Takeshi Hosaka architects decided to work with the buried feel of the site, making the entire home feel as if it’s underground without sacrificing natural light and ventilation.

On the basement level, wood-lined floors curve up to meet high windows on both the east and west sides, bringing in a breeze, with a high ceiling encouraging air flow above the living space. These windows look up at the grassy retaining wall on one end, and a small courtyard on the other.

A similar layout on the first level directs views up toward the sky. A staircase spirals through an oculus cut into each curving wall to get from one level to the next, also functioning as a skylight. The slope becomes more gradual as you rise, with even the roof following the same shape in a more subtle form, collecting rainwater and carrying it to the ground through a slit on the southern wall.

“A house with a basement and two floors above ground was planned in a residential area in Yokohama, which is characterized by rolling hills. The 60-square meter site is sandwiched by existing houses to the south and the north. On the east side, the site faces a 3m-tall retaining wall. In these ways, the site at first looked like it was buried by the surroundings.”

“In response, the design sought to pull in an equal amount of light and wind in section to both the basement and the ground level. Each floor was given the same ceiling height. The slab on each floor was bent near the exterior to give the same window size in section to each floor. When looking at the elevation, the same four sliding windows line up as if to indicate that the house, with a height of a two-story building, is three stories tall.”

“In the basement, a wind unexpected in a room located underground travels from the window on the east to the window on the west. Moreover, the core height of the furniture was set at 300mm below the slab so that the wind would travel above it. The ceiling of the concrete, which gradually rise, invites natural light to the interior. The green of the slope on the east side can be seen at the end of the rising ceiling.”