## 4 Results and Discussion
### A Case Study for the Environmental Performance Indicators in IFC
The required data structure should consist of 19 columns to represent the EPI, multiplied by all the LCA stages. In this case, it is reasonable to define multiple options considering different IFC property types and structuring approaches. Four options for structuring LCA data are described below. These options do not consider the reference to the method used to calculate the indicator (LCA impact category) to simplify the integration and testing in the pilot IFC model. The strategy of the first two options is quite similar; they have been considered as variants of the same approach and named 1A and 1B. Option 1A: Property set for each LCA stage (see Table 8): EPIs could be defined as separate property sets for each of the LCA stages, e.g. _Pset_EPIA1_, _Pset_EPIA2_, etc., using _IfcPropertySingleValue_. Option 1B: Single properties with concatenated LCA stages (see Table 9): _Pset_EPI_ or separate properties are created and all the stages are concatenated together with the single property names, e.g. _GWPtotalA1_, _GWPtotalA2_, etc., using _IfcPropertySingleValue_. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Indicators** & **Pset_EPIA1** &... & **Pset_EPIA1** \\ \hline GWPtotal & & \\ GWPfossil & & \\ GWPbiogenic & & \\ GWPluluc & & \\ ODP & & \\ AP & & \\ EPfreshwater & & \\ EPfranire & & \\ EPterrestrial & & \\ POCP & & \\ ADPE & & \\ ADPF & & \\ WDP & & \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Structure for some impact categories attributed as separate property sets with LCA stages. \begin{table}
\begin{tabular}{c c} \hline \hline
**Indicators** & **Pset_EPI** \\ \hline GWPtotalA1 & \\... & \\ GWPtotalD & \\ GWPfossilA1 & \\... & \\ GWPfossilD & & \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Structure for impact categories attributed as separate property sets with LCA stages (tabular approach). Option 2: List of property values corresponds to the LCA stages: Each list is dedicated to a specific EPI, and the list values reflect the ordered format of the LCA stage, using the element _IfcPropertyListValue_. Option 3: Using _IfcPropertyReferenceValue_ and _IfcTable_: Aligned with the tabular nature of EPD data, this approach utilizes _IfcPropertyReferenceValue_ and _IfcTable_ for enhanced data organization. To assess these options, their advantages, disadvantages, and potential limitations must be considered. Table 6 provides a comparative overview, highlighting how each approach impacts data structuring, integration with BIM authoring tools, and implementation. Each scenario has its own pros and cons as well as possible limitations in terms of data structure or implementation level. Table 10 summarizes the options analyzed during the study. Options 2 and 3 are more aligned with the EPD data structure. However, effective implementation is currently hindered by the limitations in BIM authoring tools. Even if a list or table structure is available, it is typically not integrated within BIM tools. The structure of option 1A provides a compromise and can be used to associate EPD information with building elements (_IfcElement_) that are unitary and do not have a layered structure, i.e., windows, columns, hollow slabs, etc. In the case of layered building structures (e.g., floors, walls, roofs, etc. ), the EPD provides information on specific layers of materials. Consequently, the environmental impact indicators should also be assigned to specific layers in the building model, as _IfcProperty_ for materials is used to express the individual material properties by name, description, value and unit. Option 1A cannot be applied to layer-based representations. Given these limitations and drawbacks, only option 1B can currently be applied for the integration of EPD and IFC data without additional third-party software or additional processing of data input files.