Low-density urban models, widely diffused in Spain until 2008, have been strongly criticized because they produce a great strain on the land, high infrastructure costs, increasing maintenance expenses, energy waste and pollution from excessive transport, time wasted commuting and more bedroom communities. To counterbalance this effect, opponents are claiming for a review of the capacity that the conventional city, with its higher population density and mixed uses, may still possess. One possibility that has been explored is the vertical extension of buildings, which capitalizes on the remaining buildable space characteristic of many older buildings, and at the same time, refurbishes the housing block and improves standards of energy efficiency, safety and accessibility. The challenge is not only technical - it is clear what needs to be done and how to do it - but it is also social and fiscal; in other words, how do we get organized and how do we finance such a project? The preferred construction system for vertical extensions is industrialized and uses two main materials: steel and wood. The system involves the use of two-dimensional panels and 3D pods that, once completed in the factory, are transported to the worksite, lifted by a crane and installed on the roof of the building. From refurbishing the existing building to adding the new vertical extension, the entire operation takes four months. The experience of this vision and its application in the area of the Example in Barcelona, coming soon to other central neighborhoods in Spanish cities, allows us to present our first results: the detection of over 2,000 buildings with remaining buildable space, the need to vertically extend 50 buildings and our completed projects, in some cases already inhabited, of which half a dozen are currently undergoing environmental evaluation using our own tool.