Embedded systems are used in many domains today. However, the design process of these systems is complex and time-consuming. In automation domains the complexity can be decreased by using function block based designs to specify the functionality of the system to be created. But this has to be done still manually. This paper introduces an approach to generate such function block based designs automatically from requirements. Therefore a generative approach is used, where design patterns were assembled to complete designs. The pattern description and the generation process are realized by semantic Web technologies. The evaluation of the approach is exemplified by functional schematics of room automation designs.