Rooftops & Backyards is a project/ exhibition by Bureau Spectacular at Taiwan Academy. It is a project looking at the accessory dwelling unit in the context of Taipei and Los Angeles. In the context of lacking space, user potentially to add an addition space to their property. However, people build their addition vertical in Taipei city; and Los Angeles resident added horizontally. Bureau Spectacular sees it as a potential mathematical set that combining these two condition and creating an innovative net work for public. This project shows the idea to ease the population problem as well as the spacing problem.