What is the accuracy of BIM models? How is LOD classified into levels? The creation and management of BIM models are crucial tasks in the application of BIM technology. However, at various stages of the project lifecycle, there has always been a need for clear guidelines or standards to specify the content and detail required in the models. This is especially important when contracts involve the delivery of BIM models, where both parties must agree on the expected content and level of detail. For contractors, understanding the client’s expectations is essential to accurately estimate the required resources and costs for modeling, ensuring that the delivered models meet the needs of subsequent applications.
The American Institute of Architects (AIA) document E202 defines LOD (Level of Development) as the expected level of completeness for model components at different stages of the construction lifecycle. It classifies LOD into five levels, ranging from 100 to 500. This classification has become widely accepted as a standard for explaining the content and detail in building information modeling. However, E202 provides only conceptual explanations about how model component completeness should align with different application needs at various development stages. It also suggests using a Model Element Table to define the corresponding LOD and model element author for building components based on the CSI UniFormat classification during the project lifecycle. Yet, it lacks a detailed, practical definition of LOD for individual model components.
In practice, LOD is often oversimplified and mistakenly used to describe the development level of an entire BIM model. It is sometimes confused with “Level of Detail,” leading many to believe that every component within a BIM model must become increasingly complete and detailed as the project progresses. This misconception can result in unnecessary complexity, resource overuse during model creation, and disputes during model delivery.
In reality, the content and detail of a BIM model should be driven by the information needs specific to each discipline and each stage of the project lifecycle. BIM models are rarely, if ever, a single unified model encompassing all information requirements. According to the AIA’s LOD definition, authorized uses are based on application needs, and professional engineers typically understand the BIM requirements relevant to their disciplines. Therefore, they often create separate BIM models and are aware of the LOD for each component within their models.
However, because 3D BIM models present components in clear and specific geometric shapes, early-stage components without precise geometry or positioning may be mistakenly assumed to have reached a higher LOD than they actually have, leading to misuse. To improve collaboration through better information management and communication in BIM workflows, it is essential to standardize LOD descriptions for BIM model components. This standardization supports effective information exchange among different teams and facilitates BIM model reuse.
To clarify the definition of BIM model content and detail, and to support cross-disciplinary and cross-lifecycle communication and collaboration, the BIMForum working group of the Associated General Contractors (AGC) collaborated with AIA to develop the LOD Specification. This specification builds on the LOD levels defined in AIA E202 by providing more detailed definitions for each building system.
1. The distinction between Level of Detail and Level of Development is clearly explained: Level of Detail refers to how much detail is included in the model components (input information), while Level of Development indicates the reliability of the geometric and attribute data, which affects how the model can be used.
To support cross-disciplinary collaboration, an additional level called LOD 350 has been introduced between LOD 300 and LOD 400. LOD 350 includes the interface details needed for coordination between building systems or components. The following table summarizes each LOD level:
LOD Definition
LOD 100
Model components are represented by symbols or general graphic representations. They do not need to meet LOD 200 requirements. Information such as HVAC cost per square foot or ton may come from other model components.
LOD 200
Model components are graphically represented as generic systems, objects, or assemblies with approximate quantity, size, shape, position, and orientation. Non-graphical information may also be linked.
LOD 300
Model components are graphically represented as specific systems, objects, or assemblies with defined quantity, size, shape, position, and orientation. Non-graphical information may also be linked.
LOD 350
Model components are graphically represented as specific systems, objects, or components with defined quantity, size, shape, position, and orientation, including interface details with other building systems. Non-graphical information may also be linked.
LOD 400
Model components are graphically represented with detailed size, shape, position, quantity, and orientation, including detailed drawings, manufacturing, assembly, and installation information. Non-graphical information may also be linked.
LOD 500
Model components represent as-built conditions based on size, shape, position, quantity, and orientation, validated by on-site verification. Non-graphical information may also be linked.
Currently, the detailed definitions focus on LOD 100 through LOD 400, while LOD 500 retains its original definition from the AIA. The BIMForum working group does not see the need for further elaboration beyond this.
Two important points are emphasized: first, there is no strict correlation between LOD and specific project lifecycle stages, as different building systems develop at varying speeds during design; second, there is no such thing as a BIM model with a single LOD level. Models at any stage contain components with varying LODs, and not all components can or should reach the same level simultaneously.
That sums up the topic of What is the accuracy of BIM models? How is LOD classified into levels? I hope this article helps clarify these concepts for you!
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