## 1 Introduction  
Over the past few decades, there has been a global and cross-industry digitization process. While it initially began modestly, the advent of smartphones greatly accelerated this trend. The COVID outbreak further intensified this shift, compelling a transition from in-person to digital interactions. In this digitization process, the construction industry (CI) lags compared to other sectors. Apart from the adoption of building information modeling (BIM), which is, however, often limited to the design phase and only for large projects, the adoption of digital technologies is limited. A recent report by the European Commission [1] underscores the critical and immediate necessity for a digital transformation in the CI to encompass aspects like data collection, process automation and the integration of advanced technologies for digital information and analysis. Thanks to the BIM methodology, it is possible to manage a complex and varied amount of data throughout the entire lifecycle of a building, from the material production phase, to installation and commissioning, up to decommissioning. A tool for implementing BIM is the so-called common data environment (CDE), which is a shared working environment that is capable of making the management of real estate more efficient through transparent and shared processes ([2; 3; 4]). CDEs are regulated internationally by ISO 19650 [5]. Reference [5] identifies a CDE of the appointing party and a CDE of the appointed parties. The latter are, for example, the companies, the designers, or the construction supervisors ([2]). (The Italian legislation accurately describes the methods and procedures that have to be executed so that this transfer can take place [3]. CDEs are regulated in Italy by UNI 11337.) However, today, CDEs are centralized systems that do not offer guarantees against tampering with their contents or with their history of updates (Refs. [6; 7; 8; 9]), and often,legal implications hinder their use, thus also hindering the adoption of BIM to streamline processes and speed up operations (Refs. [10; 11; 12; 13; 14]). In addition, within this digitization process, a crucial role is played by identity management. It is widely acknowledged that the internet was constructed without a foundational identity layer. Consequently, as the world becomes increasingly digitalized, we face seemingly insurmountable challenges such as a lack of control over data, privacy concerns, compliance issues, security vulnerabilities, fraud, identity theft and a cumbersome user experience. In the literature, many works describe how BIM, IoT and blockchain can interact to contribute to digital transformation in CI (see, for example, the \"cup of water theory\" [15] and works [16; 17; 18; 19; 20; 21]). This article takes a further step forward and, for deep digitalization of CI, in addition to BIM, IoT and blockchain, exploits a new identity management paradigm based on self-sovereign identities (SSIs) that empowers users to take control of their data while facilitating seamless, private, secure sharing of data on users' own terms. This presupposes a huge system, and, hence, it would be a digital twin as defined by [PERSON] et al. [22]:  
_Digital twin is not just a single platform, technology or model, but a huge system that requires a lot of advanced technical support. For digital twin applied in the whole life cycle of buildings, with the characteristics of larger system and wider stakeholders, more support is required (extracted by [22])._  
Our model leverages blockchain, BIM and SSI to tackle counterfeiting, waste, supply chain inefficiencies, lack of transparency, lack of trust, constant use of paper, long lead times for the processing of different activities and the lack of efficient sharing of documents and information. Precisely, we present a model in which all users can operate through their decentralized digital identities and exchange data using the typical mechanisms of the SSI paradigm.