The simple guide to everything you need to know about LODs (Level of Definition/Development) in BIM
If you work in BIM, you’ve probably come across the different types of acronyms and abbreviations, some of which may have different meanings behind them. If that’s the case, you may have wondered what LOD in BIM is or what LOD 300, 400, 500 means or what’s the difference between LOD 1 and LOD 100 and what are LOINs? After reading this article, I’m pretty sure you’ll finally learn all the details behind the meanings of these indicators and what their main differences are.
Furthermore, if you are interested in BIM, we recommend you to immediately test a collaboration platform that allows you to explore an integrated system of applications and functionalities to manage the digitalization of constructions and infrastructures ina simple and secure manner.
LOD BIM definition
The term LOD is an acronym that has two different meanings, depending on whether you consider its English or American definition.
For the English LOD indicates the “Level of Definition” of the architectural BIM model and is a concept introduced by PAS 1192.
For Americans, however, it is the “Level of Development” of an element of the BIM model. In this case the term “level of development” was preferred to the term “level of detail” in recognition of the fact that a very detailed graphical element does not always correspond to a high level of actual development of the project.
Moreover, the LOD is divided into a scale in which a standard nomenclature is assigned to each level (which varies according to the reference legislation) which defines the quantity and quality of the data included in an architectural model.
In simple terms, the LOD defines the content of a BIM project in different stages of its development and grows as the project progresses and is enriched with details, evolving from a simple initial concept to a construction model.
The LOD consists of 2 elements:
- the geometry or visual representation of a project – LOG (Level of Geometry);
- the data attached to the objects of the BIM model – LOI (Level of Information).
The attached data creates intelligent objects and distinguishes simple modelling of shapes and extrusions from BIM modelling.
Let’s see what LODs are defined by the American and UK experience.
From LOD 100 to 500: the American experience
The AIA (American Institute of Architects) has published a LOD framework for the AIA G202-2013 Building Information Modelling Protocol in order to suggest a standard framework representing the different level of development of each element of the project and to facilitate communication and data exchange between the different stakeholders involved.
The levels of development established are:
- LOD 100 (symbolic representation) – is the elementary model of the project and is represented graphically with a symbol or other generic and schematic representation;;
- LOD 200 (generic system) – the model element is graphically represented within the model as a generic object with still approximate quantity, size, shape, position and orientation. Non-graphical information may also be attached to the geometric elements;
- LOD 300 (specific system) – the model element is graphically represented within the model as a specific system, in which the object has specific quantities, dimensions, shapes, position and orientation. Non-graphic information is also linked to the geometric elements, which is more in-depth than the previous level;
- LOD 400 (fabrication) – the model element is graphically represented within the model as a specific system, in which the object has specific dimensions, shape, position, quantity and orientation with further details for its fabrication, assembly or installation. More in-depth non-graphical information is linked to the geometric elements than in the previous level;
- LOD 500 (verified representation – as built) – the model element is a verified representation on site in terms of size, shape, position, quantity and orientation. Definitive non-graphical information is linked to the geometric elements.
BIM LOD UK
In the UK, the Construction Industry Council (CIC) first published a BIM protocol in 2013 in response to the government’s strategy and set a deadline for Level 2 BIM compliance for publicly funded projects by 2016.
The CIC BIM protocol defines responsibilities, limits and deliverables of project team members at key stages of the process corresponding to a specific ‘level of detail’.
The stages are essentially similar to the US definitions, although they are numbered differently.
The UK definitions in PAS 1192 are the following:
- LOD 1 (brief) – block model with performance requirements and site constraints;
- LOD 2 (concept) – conceptual or volumetric model including basic areas and volumes, orientation and cost;
- LOD 3 (developed design) – generalised systems with approximate quantity, size, shape, location and orientation;
- LOD 4 (production) – technical design model with accurately modelled and coordinated elements that can be used to estimate costs and verify regulatory compliance;
- LOD 5 (installation) – model suitable for construction and assembly, with accurate requirements and specific components;
- LOD 6 (as constructed) – a model with details describing how the asset has been constructed and which can be used in the operation and maintenance phase;
- LOD 7 (in use) – a model of asset information to be used for ongoing maintenance and monitoring operations.
LOIN: the evolution of the LOD
Usually, in order to protect themselves from possible information gaps, professionals tend to exaggerate with the amount of information to be communicated. In this way, they make the mistake of producing and sharing an excess of information that is often useless.
In order to overcome this problem, ISO 19650-1 introduced the concept of Level of Information Need or LOIN, in fact enhancing the concept of LOD.
The name itself denotes a change of perspective: the focus is no longer on the characteristics of the object but on the need for information that the object must contain to satisfy the professional’s requirements at that precise moment in the design process.
The concept of LOIN starts from the awareness that the degree of a model’s depth is not an absolute parameter but is to be evaluated according to different conditions.
The information requirement level describes the granularity of the information exchanged in terms of geometric, alphanumeric and documentation information.
Let us take an example.
If we were to prepare project drawings to be handed over to the window and door manufacturer to place an order, it would be necessary to have a high degree of detail on all the information required for this purpose (type of window and door frames, presence of thresholds, type of door frames, size of voids, direction and type of sash opening, etc.), while it would be completely useless to go into the same degree of detail on, for example, information relating to the heating system, false ceilings, etc. This difference in the degree of information detail within the same model is called granularity.
In practice, the information requirement levels indicate how much and what information should be included in each object based on:
- purpose (why?);
- deadlines (when?);
- stakeholders involved (who?);
- organisation into one or more breakdown structures (what?).
LOINs never specify purposes, deadlines, actors or breakdown structure, precisely because the same Needs Level may serve several purposes, actors, etc.: it is its placement within a general framework that will specify its uses.
The information needs level is given by the combination of 3 types of information:
- geometric, expressed using shape, size and position;
- alphanumeric, expressed using characters, digits, symbols, etc.;
- documentation, i.e. the set of documents relating to a specified subject.