To ensure public safety, major cities in the U.S. have façade ordinances that require periodic façade inspections and reporting of façade conditions. Our shadowing works show that the current inspection processes are based on inspectors' experience rather than systematic inspection guidance. Besides, façade inspectors have different preferences to group their inspection findings (e.g., grouping inspection results based on a defect type or façade component), resulting in a need to provide flexibility to inspectors to organize façade inspection results based on their preferences. Building Information Modelling (BIM), with the ability to support storage, extraction, and exchange of facility information, can help with a systematic and comprehensive inspection of façades and store and exchange the façade inspection results with the third parties. To enable model-based guidance for a comprehensive inspection of any given building and to bring flexibility to restructuring the model and inspection data based on inspector preferences, an essential step is to define information requirements and develop a generic data representation for façade inspection. We have identified a generic taxonomy of façade components, defect types, defect attributes, and the relationships among the identified elements to enable comprehensive façade inspection guidance and flexible restructuring of the inspection findings. This paper provides the details of data exchange requirements and the initial ontology for a model-based façade inspection process. The ontology builds on the Industry Foundation Classes (IFC) specification and extends it to include entities, attributes, and property sets required for model-based façade inspection. This work provides the underlying data representation requirements for supporting the reasoning mechanisms that take a model as an input, generate a comprehensive checklist for inspection, and enable grouping façade elements flexibly based on inspector preferences for inspection data storage and visualization.