Japan is undergoing a period of change. A succession of buildings with common characteristics are rising within the fabric of Japanese metropolises like trees in a dense forest of buildings.These buildings are distinguished by their great slenderness and their reduced floor space. They call them “Penshirubiru”, which can be translated as pencil buildings.These are multi-purpose buildings, often dedicated to collective housing, although exceptionally there is also the case of a house-building for a single owner. They have an extremely small footprint, so much so that only the area dedicated to vertical communications can occupy half of the floor. They rise in height above these minimal plots forming slender pieces, like a pencil standing upright, hence their name. When they appear grouped on the same street, it is inevitable to recall the image of a half used pencil box, each worn down to a different length.This new housing is undoubtedly a response to the new social model that has generated a majority of single-person households and a citizen economy also based on this marked individualisation and on the current daily routines that tend to reconcentrate citizens around very dense areas with a great mix of uses.