# Building Information Modelling Facility Management (BIM-FM)
## 7 Theoretical Requirements for BIM-FM
### Theoretical Modelling Requirements  
For FM purposes, a geometrically simplified BIM is usually considered sufficient due to the importance placed on the descriptive detail associated with objects [34; 52]. In their review of the purposes of BIM for FM in Corporate Real Estate Management (CREM), [PERSON] and [PERSON] [49] found that BIM-FM users established visualisation to be the lowest priority in BIM for FM development. Furthermore, [PERSON] et al. [46] conducted a study investigating a company with a high level of both BIM maturity and practical application and found that the company switched from 3D models to 2D CAD objects due to a lack of any real benefits of a 3D model. Another justification for model simplification is that FM managers are unlikely to have access to sophisticated computers, so geometrically complex models will result in a non-optimal user experience, as [PERSON] et al. [52] found when they tested models of three different complexities on two computers of differing quality (i.e., processing power and graphics capabilities). [PERSON] and [PERSON] [12] also found that complicated model objects reduced the performance of the model. They opted to use simplified generic models with some resemblance to the real condition, as opposed to low-complexity symbolic models, so that objects could be recognised more easily. Photography is a key resource for FM as much necessary information can be inferred from an image. This may explain why simple models are often considered sufficient. However, accessing and organising this information is exceedingly difficult especially when an asset has a long service life or is complex in nature [85]. Theoretically, a point cloud could provide the same information in a more understandable format as evidenced in [PERSON] and [PERSON] [88], who designed a BIM-FM system for a wastewater treatment plant. They collected data using laser scanning and then separated the points referring to each water pump into regions in Autodesk Recap 360. There were no apparent issues reported with this as all the pumps could be visually distinguished, and the required maintenance information was linked to each colour-coded region. The integration of accurate point clouds with simplified geometric models could serve as an effective compromise for BIM-FM, whilst acknowledging the likelihood that sophisticated software systems may not be available. Whilst acknowledging that complicated models experienced system performance implications, [PERSON] and [PERSON] [74] carried out focus groups with FM practitioners and found that they required a minimum Level of Development (LOD) of LOD 350 with some participants requesting LOD 400, both of which require highly precise geometric representations [89]. The authors were specifically investigating HVAC systems, where the use of high geometric accuracy models has been previously established as a requirement by the BIM community [90], so this may not be indicative of all building elements. However, there are other notable arguments against model simplification for FM. For instance, to utilise quantity take-offs for cost estimation, the geometry must be reasonably accurate [59]. [PERSON] et al. [61] discussed the need to aggregate individual model elements from the design stage into larger, simplified components during the asset management stage. However, this is contradicted by [42], who state \"one would conduct very different activities if a defect was identified for a wall finish than for a wall's structural layer\"; thus, there is a need for some granularity of data and additional semantic meaning. Based on the evidence, it seems to the authors of this current paper that the tendency to utilise simplified BIM models for FM may be due to the difficulties of creating and utilising a complex model, as opposed to the actual need of BIM-FM end users. The previously apparent simplified modelling requirements [34; 52] for FM may also explain the lack of research into advanced model creation in BIM-FM. Notable exceptions include [PERSON] et al.