A research on how to design affordable and sustainable housing for those affected by the gap in the housing market. It is getting more and more difficult for certain people to find suitable and affordable housing. They earn too much for social housing, but too little for the private sector or an owner-occupied housing. Especially in the city this group of people is slowly pushed out and sometimes forced to find housing elsewhere. This has a negative effect on the personal and financial growth of this people, but also on the economic, social and sustainable growth of the city itself. This research has been divided in three parts; [1] The gap in the housing market (the issue and its consequences), [2] the post-war neighbourhood, Zuidwijk (the social-historical context), and [3] sustainability (people, planet, prosperity). The target groups, those affected by the gap in the housing market, play a big role within this research. This is necessary to understand for whom you are designing and what needs to be done to solve the issue; this is part of the social sustainability. Certain questions need to be answered: who are they; what issues do they encounter; what are their living requirements; what can they actually afford? Design principals, requirements and limitations will follow from each research parts. These may summarise and translate the finding in each chapter and can be used as tools when coming to a design.