## 5 Conclusions  
The IRIS project offers a compelling framework for leveraging DT technology to address the complex challenges inherent in engineer-to-order manufacturing. By integrating IoT, BIM, and AI capabilities, the DT architecture can support warehouse management in customized prefabricated building product manufacturers, as in the case of Focchi S.p.A., creating a more efficient, safe, and data-driven environment. The DT architecture design serves as a practical blueprint for the implementation of digital twin technology in ETO manufacturing environments. By integrating IoT, BIM, and AI, the DT appears to offer a comprehensive solution for optimizing warehouse operations, enhancing worker safety, and streamlining complex workflows. The project's findings can be directly applied to similar manufacturing contexts where customization and rapid response to construction site demands are comparable. The developed framework, encompassing data collection, analysis, and visualization, can be adapted to various warehouse layouts and production processes. The focus on user-centric design ensures that the resulting DT is intuitive and user-friendly, promoting widespread adoption and maximizing the benefits of digital transformation. Moreover, this research's emphasis on safety protocols and risk mitigation strategies can serve as a model for other industries seeking to improve workplace safety with digital technologies. A key remark is that this research underscores the importance of a user-centric approach in DT design, as exemplified by the meticulous collection of user stories and requirements. By tailoring the DT to the specific needs of warehouse personnel, this research demonstrates the potential for technology to empower workers and improve their daily experiences. Despite these achievements, a limitation of this research lies in the replicability evaluation. The current methodology and design were assessed for a single, specific use case. While this use case may be representative for ETO companies in building product manufacturing, a broader validation across companies with similar ETO manufacturing requirements is needed to demonstrate the effectiveness of the proposed design to check the potential risks associated with scaling this solution in the future. Even though this DT design represents a significant first step towards integrating such solutions within the engineer-to-manufacturing process for building products, its scalability remains a concern. This initial assessment serves as a valuable foundation, but further investigation is necessary to determine the solution's applicability to other similar companies within the building product industry, as well as in adjacent industries with comparable characteristics. While implementation of DT architecture is ongoing, and consequently subject to testing activities, the design and development phases of a DT for ETO manufacturers have highlighted the transformative potential of a digital twin. The integration of real-time data, 3D visualization, and AI-powered analytics can unlock new levels of efficiency, optimize resource utilization, and enhance safety protocols. However, the design validation should be confirmed with DT implementation focusing on rigorously quantifying its impact on key warehouse KPIs defined with the users. This will provide concrete evidence of the DT's efficacy in ETO environments. This will serve to demonstrate design methodology effectiveness for DT implementation in the specific ETO context. Further research should investigate the scalability and adaptability of this approach to other industries and manufacturing models, potentially leading to standardized DT frameworks for broader adoption. This validation is even more interesting considering the understanding of the impact of the DT on worker behavior and decision-making, crucial for long-term success. Futurestudies should investigate the human-machine interaction aspects of DT implementation, ensuring that the technology complements and empowers the workforce.