## 1 Introduction
### Building Information Modelling for FM  
The United States National Institute of Building Sciences (NIBS) defines BIM as \"The digital representation of physical and functional characteristics of a facility. As such, it serves as a shared knowledge resource for information about a facility, forming a reliable basis for decisions during its life cycle from inception onwards\" [22].  
In recent years, BIM has been more and more employed in the AECO sector to improve information management. BIM Models (BIMs) allow integrated management of information throughout the building's entire life cycle, hence improving FM [23]. On the one hand, BIM allows working more efficiently during the design and construction phases by developing a 3D model that avoids project interference and allows project time and cost calculation. On the other hand, it allows acquiring data created during several phases of the building life cycle to use them in operations management, maintenance activities, environmental analysis and energy performance simulations. The latter is related to Building Energy Modelling (BEM), which has become an essential aspect for FM.  
Benefits of using BIM in FM include providing \"as-is\" information and enabling Facility Managers to work on information using a single source of data, overcoming all the issues deriving from the sources' fragmentation.  
A BIM model has different Levels of Information Needs [24]. To deal with them, the American BIMForum defined the Level of Development (LOD) Specification. This reference enables practitioners in the AEC Industry to specify and articulate with a high level of clarity the content and reliability of Building Information Models (BIMs) at various stages in the design and construction process. A BIM model has six Levels Of Development (LOD): LOD 100, LOD 200, LOD 300, LOD 350, LOD 400 and LOD 500 [25]. Each LOD defines how much information is included in a building component. The higher the LOD, the greater the clarity and reliability of data and information.  
According to [PERSON] et al. [26], using the highest LOD is possible in order to enrich the digital model with all the information necessary for assets management and maintenance. In this way, data are more efficiently stored in a single file without fragmentation or loss of information. Moreover, improving the handover process is possible using fewer paper documents or manual transfer of information [26].  
As early as 2012, [PERSON] et al. [27] have defined, also through surveys and interviews, how BIM can support FM practices. Their paper assesses the status of BIM implementations in FM, potential applications, level of interest in BIM utilisation, application areas, and data requirements for BIM-enabled FM practices. To date, studies on BIM application in FM confirm momentum (e.g., [18; 28; 29; 30; 31; 32; 33]).  
However, despite all the advantages, BIM is not often used in the FM phase. The most significant causes that hinder this integration are:  
1. Industry perception, which considers BIM models just as 3D models and not as informative models with business value [34].
2. Lack of involvement of the facility managers in the creation of the BIM model [7; 35]. Consequently, less information useful for FM is integrated into the model.
3. The need for interoperability between BIM and FM technologies and the lack of open systems and standardised data libraries that can be utilised as a bridge between BIM and CAFM technologies [36].
4. Lack of clear roles, responsibilities, contract and liability framework [36].
5. Furthermore, the main limitation of BIM methodology is its static information: data are provided during the design phase but not updated during the building's life cycle [37]. This is a relevant issue for buildings management, and research is moving in this direction.