One of self-construction’s motivation comes from the fact that it is difficult for the authority to control and thus, sometimes its illegal existence for a more or less important time. That is one of the topics tackled by Robert Neuwirth in his book, Shadow cities. A billion squatters, a new urban world. In fact, for his research, this author lived for a while in one of Rio’s favelas and other illegal district in Nairobi (Kenya), Mumbai (India) and Istanbul (Turkey). For each city, he is interested in observing how these districts’ inhabitants manage to negociate with their environment’s illegal existence thanks to a bypass or an interpretation of the law, which allow their juridical eviction to be more difficult. That is how we learn that, a Turkish law affirms that an illegal building in construction can be destroyed immediately whereas, an achieved building could only be demolished after judiciary proceedings. Therefore a lot of buildings are built very quickly during the night, to limitate as possible the vulnerability period. It is then interesting to observe how the bypass of law influence architecture and become a collective tacit knowledge which rules the district organisation.