This small three-story house is built on a 40m2 lot located in a residential district, which is a few minutes walk from the main road. It is a densely built- up area with small two- or three- story houses, representing a common living condition in Tokyo. Therefore our client’s request reflected common demands of urban residents: they wanted living space that is ‘closed’ for security and privacy, but also ‘open and bright’ with sufficient natural light inside. Due to limited budget and modest lifestyle, the house is a simple three-story house of wood construction, with each floor accommodating different function. Building height and ceiling heights are automatically determined by north side slant line regulation. We intend to create a sense of spaciousness in this small volume. In order to maximize the verticality we provide living/dining/kitchen space adjacent to stairway on the ground floor, so that they can experience the full height of the volume from there. By placing concrete block fence along the site border we create semi-interior zone between the walls and the house, so that the interior space is visually extended to the full extent of the site. We also want to provide various conditions of light on each floor. On the ground floor the entire space is illuminated with indirect light coming from above through the semi-interior zone and stairway, creating soft and diffused effect like artificial lighting. On the contrary they can enjoy direct natural light coming in from windows on the second and third floors.