The Dutch elderly housing system has a gap for vulnerable elderly. The Dutch policy on elderly care is to continue living at home for as long as possible and moving into a nursing home with 24h care when living at home is not possible anymore. However, a large group of elderly is not served by this policy. This group is the group of so called vulnerable elderly. Living at home might be tough for them because of the incidental care they need, but moving into a nursing home is unnecessary. For these groups of elderly a new housing form is needed. In order to create this new housing types, transformation of existing vacant buildings could be a solution. Empty plots to build on are become increasingly more scarce and with the climate crisis the existing building in The Netherlands should be renovated in order to improve their sustainability. In this thesis research was done on what design guidelines would be needed in order to create a new social housing complex out of an existing building. The results show that a form of co-housing with mixed living for elderly could be a solution. In these co-housing complexes the emphasis lies on creating social connections through shared spaces. These social connections improve both mental and physical health, whilst at the same time relieving pressure on the Dutch care system by increasing informal care between resident. The results of this investigation are a number of design guidelines which need to be implemented in an existing utility building for transforming this building into a succesfull co-housing for elderly. These desgin guidelines are combined into a building concept showing the basic design ideas for creating a senior co-housing complex with mixed living.