This paper presents a design for a topology-optimised concrete floor slab, of which the structural optimisation process is guided by manufacturability constraints from a vacuumatic formwork. Ihe design has been obtained using an open-source, tliree-dimensional topology optimisation algorithm. Traditional floor systems are cost-optimised but can have the disadvantage of being structirrally inefficient. Topology opthnisation allows for efficient material distribution, and thus a reduction in weight. Topology-optimised floors are typically regarded as being difficuft to produce, however, and cost too much to be considered in building designs. In order to reach a compromise between a low self-weight and low production costs, two features are included in the optimisation process. First, manlifacftirability is directly incorporated in the optimisation, rather than afterwards. Secondly, the highly malleable vacuumatic formwork system by Huijben [7] has been used as a premise. Its advantages may cause the formwork costs to be reduced considerably when producing floor slabs.