Modern building automation systems consist of up to 30,000 components (e.g. sensors, actuators, and controllers). Additionally, different assembly sections of the automation system, e.g. heating, ventilation, and lighting, are integrated in such a building automation system. Besides this complexity, engineering standards and aspects of energy efficiency are to be considered within the Requirement-Elicitation phase. Therefore, modelling of the requirements for decentralized building automation systems, which are to be planned, requires a huge effort. The software support is on a low level within today's Requirement-Engineering phase. This allows to optimize the engineering process in building automation. The whole engineering process can benefit from an "intelligent" softwarebased Requirement-Engineering. Within this paper, the authors propose a solution for a knowledge-based RequirementEngineering software by means of Semantic Web technologies.