From the Architects:
The house is built on a sloping site, and in order to minimize the excavation work the rear half of the house is dug into the ground, the excavated earth being used as fill for the front half, creating a level floor. The floor surface at the embedded rear part of the house curls up to meet the roof, naturally absorbing the imposed load of the earth. The roof is flat and is fixed rigidly to the upturned slab freeing the 3 columns at the front from any horizontal loads. As a result of bearing only vertical loads these columns could be reduced to a minimum 55 mm in diameter. In order to express the structural concept as purely as possible all the walls and mullions have been purged leaving only sliding panels. Spatially, the house consists of a ‘universal floor’ on which the kitchen, bathroom and toilet are all placed without enclosure, but which can be flexibly partitioned by the sliding doors.
For more information about Shigeru Ban's 2014 Pritzker Prize, please read http://www.architectmagazine.com/architecture/shigeru-ban-architects-wins-the-2014-pritzker-prize_o.aspx