## 4 Results and Discussion
### A Case Study for the Environmental Performance Indicators in IFC
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Option** & **IFC Property Type** & **Advantages** & **Disadvantages** & **Limitations** \\ \hline \multirow{4}{*}{1A} & \multirow{4}{*}{IfcPropertySingleValue} & Embedded in the majority of BIM authoring and IFC editing tools. & Large number of property sets and properties. & Not suitable for layer-based representation (e.g., material layers) or assembled IFC elements. & Not suitable for layer-based representation (e.g., material layers) or assembled IFC elements. & \\ \hline \multirow{4}{*}{1B} & \multirow{4}{*}{IfcPropertySingleValue} & Embedded in the majority of BIM authoring and IFC editing tools; suitable for layered/assembled IFC elements. & Large number of properties. Complex property names (concatenated). & Not all BIM authoring tools have the ability to create custom property sets. \\ \hline \multirow{4}{*}{2} & \multirow{4}{*}{IfcPropertyListValue} & Requires up to 19 times less properties (EPIs) compared to scenarios 1 and 2. & Requires metadata about the sequence (list order). & No integration with IFC editing tools. \\ \hline \multirow{4}{*}{3} & \multirow{4}{*}{IfcPropertyReferenceValue} & The best scenario in terms of data structuring. & The entities are not part of a standardized IFC schema subset or implementation level. & No integration with BIM authoring and IFC editing tools. \\ \cline{1-1}  & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Summary of approaches (options) to attribute LCA data in a revised IFC standard. To test the proposed approach, option 2 was adopted for the pilot building, storing environmental data from EPDs accessible from manufacturers or POs. This option provides _IfcPropertySingleValue_ entries for each EPD indicator-stage combination, i.e., a property named _GWPlotAlA1_ for global warming potential value for module A1 (see Figures 3 and 4). This approach was selected following an evaluation of available options to integrate the tabular data from EPDs into IFC. A typical construction EPD according to EN 15804+A2 comprises nineteen environmental impact categories across multiple life cycle stages. In order to perform the assessment, it is also necessary to consider other environmental indicators related to waste generation, transport, and other parameters. Option 1B (name concatenation) stores each value as an individual property with the stage appended to the name, which can be easily implemented in any BIM tool. However, incorporating a phase in the name of an indicator deviates from the consistent standard naming conventions. In summary, _GWPlotA1_ is not a formally standardized property identifier, but rather an application-specific convention. In addition, it does not include the calculation method. Figure 4: Integration of environmental indicators for the A1–A3 information modules for layered elements. Figure 3: Integration of information modules A1–A3 for a product. However, this trade-off was considered acceptable in the pilot for practicality and for integration purposes for single projects, as it allows the embedding of EPD data directly in the IFC using standard mechanisms, such as property values. This action can be performed with most of the modelling tools without requiring specific IFC extensions. This approach may enhance EPD data integration into BIM projects. However, machine interpretation will require the integration into the official IFC schema to support EPD data integration in a structured and efficient way. Overall, option 1B combines standardization and usability by utilizing the basic structure of the IFC schema to integrate EPD data, while recognizing that more standardized solutions (i.e., IFC tables or complex attributes) would be more advantageous if they were integrated into BIM authoring tools. The accuracy of the values will be dependent on the background data and rely on the BIM tool. The reliability of BIM authoring tools or IFC viewers was not considered during the study and should be assessed in future research.