Last edited 15 Mar 2022

Level of detail for BIM

Building Information Modelling is a very broad term that describes the process of creating and managing digital information about a built asset such as building, bridge, highway, tunnel and so on.

The level of detail of a building information model increases as the project proceeds, often based in the first instance on existing information, then developing from a simple design intent model through to a detailed virtual construction model, then an as-constructed asset information model (AIM). Different aspects of the model may develop at different rates, may originate with different members of the project team, and their development may pass from the employer, to consultants, to the contractor and suppliers and ultimately back to the employer.

It is important therefore that the employer defines the level of detail that is required at each stage of development of the project. This not only ensures that the design is developing in sufficient detail, but also that the information required by the client to make decisions about the project development and then to operate the completed project efficiently, is actually provided. It also gives an indication of the reliance that can be placed on information.

The employer defines the level of detail that is required in the Employer's Information Requirements (EIR). The Employers Information Requirements might be appended to a BIM protocol, incorporated into the contract by addition of a 'model enabling amendment', making the delivery of required information a contractual obligation.

A summary of level of detail requirements and responsibility for model development might be provided in a Model Production and Delivery Table.

PAS 1192-2 Specification for information management for the capital/delivery phase of construction projects using building information modelling (now replaced by BS EN ISO 19650) defines two components to the 'level of definition':

In fact, the two are closely aligned as it is normal for graphical and non-graphical content to develop alongside one another.

The levels of model detail and model information are generally defined for key stages of the project, at which 'data drops' (information exchanges) take place, allowing the employer to verify that project information is consistent with their requirements and enabling them to decide whether to proceed to the next stage. This is analogous to a stage report on a conventional project.

As present, there is no standardised definition for the timing of data drops or for levels of model detail and model information, other than the suggestion that they should be aligned to employer decision points and should be consistent across all appointments. This is because it is thought they will vary depending on the nature of the project. However, some very broad guidance is given in PAS 1192-2:

The NBS BIM toolkit, developed following a government competition can be used to help define information requirements for projects aligned to specific project stages.

The American Institute of Architects (AIA) has also published a LOD framework for the AIA G202-2013 Building Information Modelling Protocol Form. Here LOD refers to the 'Level of Development' required for model element content. The term 'level of development' is used rather than 'level of detail' in recognition of the fact that a visually very detailed element might in fact be generic and despite appearances might be at a low level of design development.

The AIA suggest that the LOD framework recognises that different elements of the project will develop at different rates and '…allows the Project Participants to efficiently communicate to one another the extent to which a Model Element has been developed … It also allows the Project Participants to communicate the extent to which a Model element may be used and relied on…'

The LOD framework defines the following model element content requirements:

Ref AIA, Guide, Instructions and Commentary to the 2013 AIA Digital Practice Documents.

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Sería muy interesante que las principales Bibliotecas BIM introdujeran en sus filtros de búsqueda la 'categorización' LOD.

Un saludo

Borja S.Ortega

Designing Buildings Anywhere

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