This paper discusses identification and decomposition of empty spaces in Computer Aided Design (CAD) model for detecting spatial conflicts across multiple design domains. An Algorithm has been developed to identify empty spaces in CAD model and decompose it to a level, where it can be correctly associated with the connected domains, states and requirements. Knowledge capture and representation have been demonstrated with System Modelling Language (SysML) diagrams using SysML tools. SysML blocks have been introduced to define intended empty spaces, product states and design domain in SysML structure diagrams. Association of these blocks with neighboring parts, has also been discussed. A case study of heat sink assembly has been taken for Empty space modelling.