For the calculation of flexible rafts, the rising structure is often not taken into account on the design with the exception of the load transfer location. Mostly, a uniform stress distribution is assumed below a footing, even though this is only valid if the footing is totally flexible and is able to follow the movement of the soil at every point. The assumption of flexibility is dependent on load and stiffness of the footing while already both, the flexible raft made of concrete as well as the structure itself are influencing the stiffness of a raft. Local stiffening of the foundation, e.g. by locally increased thickness of the raft or flexural rigid connected walls, is not taken into account in the design approach. In this contribution centrifuge model tests are carried out for different raft systems to explore the development of the stress distribution under a flexible raft foundation. Focus is given to identify the influence of the stiffening effects of outside walls for structures mostly loaded via middle columns.