## 2 Background
While LCC is typically performed as a separate process, its integration into structured BIM workflows, particularly through IFC-based models, can enhance the evaluation of long-term cost-effectiveness, using metrics, such as payback periods, for retrofit interventions [22; 25]. Recent developments in BIM workflows have increasingly emphasized structured and automated approaches to cost estimation. Standardized IFC models are used to define cost items and link them directly to building components, enabling more consistent and scalable evaluations [9]. This structured integration supports scenario-based comparison of retrofit strategies, aligning technical performance with long-term cost efficiency [10]. Despite advancements in BIM-based cost estimation, current workflows still face critical limitations in integrating cost and energy data due to fragmentation, lack of standardization, and limited semantic support for automation. Cost estimations, energy reports, and material specifications are often stored in separate environments, making consistent and scalable evaluations difficult [26; 27]. In particular, differences in pricing structures, currency formats, and update mechanisms continue to constrain BIM interoperability [28]. Related work by [29] proposed a BIM-based method to improve IFC interoperability for energy audits using custom property sets, but it did not address cost-energy integration or support scenario-based evaluation. Additionally, a recent study by [29] highlighted persistent interoperability issues in IFC-to-BEM workflows, especially for integrating energy simulation outputs. Furthermore, the authors of [30] highlighted the IFC format's lack of support for time-series data, the challenges associated with geometric data extraction, and the absence of standardized toolchains for converting IFC files into usable formats. Beyond interoperability and semantic limitations, practical challenges continue to affect the consistency of BIM-based cost estimation. Market dynamics, including fluctuations in material and labor prices, also influence the reliability of cost assessments. Since most BIM models do not support dynamic cost updates, estimation consistency is often affected. While partial automation through scripting is helping address this issue, many workflows still rely on manual data entry, introducing inefficiencies. Linking building objects directly to cost elements remains a challenge in improving BIM-based cost assessments [31; 32; 33]. While BIM has supported more advanced cost estimation methodologies in recent years, its integration of energy data for evaluating retrofit costs is still limited. However, IFC provides the potential to represent cost- and energy-related data in a unified model, but its application in retrofit analysis is still developing. To address these limitations, the integration of parametric energy data into cost-linked IFC workflows remains unexplored. In this study, both energy simulation outputs and cost data are embedded directly into IFC models, enabling semi-automated and interoperable evaluation of multiple retrofit scenarios. Addressing existing gaps in data standardization, cost updating processes, and object-cost associations is important to improve the consistency and applicability of BIM for retrofit cost assessment.