All practitioners who use Building Information Modelling tools and workflows in their daily practice must have already faced the ‘information exchange dilemma’. That is, to effectively deliver a project, it is first essential to define what information is needed, from whom, and at what level of detail.
The Level of Development (LOD) Specification is a reference that 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. The LOD Specification utilizes the basic LOD definitions developed by the AIA for the AIA G202-2013 Building Information Modelling Protocol Form and is organized by CSI Uniformat 2012. It defines and illustrates characteristics of model elements of different building systems at different Levels of Development. This clear articulation allows model authors to define what their models can be relied on for, and allows downstream users to clearly understand the usability and the limitations of models they are receiving. The intent of this Specification is to help explain the LOD framework and standardize its use so that it becomes more useful as a communication tool. It does not prescribe what Levels of Development are to be reached at what point in a project but leaves the specification of the model progression to the user of this document. To accomplish the document’s intent, its primary objectives are:
- To help teams, including owners, to specify BIM deliverables and to get a clear picture of what will be included in a BIM deliverable
- To help design managers explain to their teams the information and detail that needs to be provided at various points in the design process
- To provide a standard that can be referenced by contracts and BIM execution plans.
It should be noted that this Specification does not replace a project BIM Execution Plan (BEP), but rather is intended to be used in conjunction with such a plan, providing a means of defining models for specific information exchanges, milestones in a design work plan, and deliverables for specific functions.
The intent of this page is to help explain the LOD framework and standardize its use so that it becomes more useful as to help design managers explain to their teams the information and detail that needs to be provided at various points in the design process
LOD Specifications can also provide a standard that can be referenced by contracts and BIM execution plans.
Levels of Development
The Level of Development (LOD) framework addresses several issues that arise when a BIM is used as a communication or collaboration tool, i.e., when someone other than the author extracts information from it:
During the design process, building systems and components progress from a vague conceptual idea to a precise description.
In the past there has been no simple way to designate where a model element is along this path. The author knows, but others often don’t.
It’s easy to misinterpret the precision at which an element is modelled. Hand drawings range from pen strokes on a napkin to hard lines with dimensions called out, and it’s easy to infer the precision of the drawing from its appearance. In a model though, a generic component placed approximately can look exactly the same as a specific component located precisely, so we need something besides appearance to tell the difference.
The LOD framework allows model authors to clearly state the reliability of given model elements, so the concept becomes “Since some of the information in the model is unreliable, you may only rely on it for what I specifically say you can.”
In a collaborative environment, where people other than the model author are depending on information from the model in order to move their own work forward, the design work plan takes on high importance – it is necessary for the model users to know when information will be available in order to plan their work. The LOD framework facilitates this.
The LOD Framework addresses these issues by providing an industry-developed standard to describe the state of development of various systems within a BIM. This standard enables consistency in communication and execution by facilitating the detailed definition of BIM milestones and deliverables.
Level of Development vs. Level of Detail
Level of Detail is essentially how much detail is included in the model element. Level of Development is the degree to which the element’s geometry and attached information has been thought through – the degree to which project team members may rely on the information when using the model. In essence, Level of Detail can be thought of as input to the element, while Level of Development is reliable output.
Fundamental LOD Definitions
The Model Element may be graphically represented in the Model with a symbol or other generic representation, but does not satisfy the requirements for LOD 200. Information related to the Model Element (i.e. cost per square foot, tonnage of HVAC, etc.) can be derived from other Model Elements.
The Model Element is graphically represented within the Model as a generic system, object, or assembly with approximate quantities, size, shape, location, and orientation. Non-graphic information may also be attached to the Model Element.
The Model Element is graphically represented within the Model as a specific system, object or assembly in terms of quantity, size, shape, location, and orientation. Non-graphic information may also be attached to the Model Element.
The Model Element is graphically represented within the Model as a specific system, object, or assembly in terms of quantity, size, shape, orientation, and interfaces with other building systems. Non-graphic information may also be attached to the Model Element.
The Model Element is graphically represented within the Model as a specific system, object or assembly in terms of size, shape, location, quantity, and orientation with detailing, fabrication, assembly, and installation information. Non-graphic information may also be attached to the Model Element.
The Model Element is a field verified representation in terms of size, shape, location, quantity, and orientation. Non-graphic information may also be attached to the Model Elements.
Example – light fixture:
- 100 cost/sf attached to floor slabs
- 200 light fixture, generic/approximate size/shape/location
- 300 Design specified 2×4 troffer, specific size/shape/location
- 350 Actual model, Lightolier DPA2G12LS232, specific size/shape/location
- 400 As 350, plus special mounting details, as in a decorative soffit
Several classifications (included in Table 2) are already established. However, it is important to underline that – while many share the same name/acronym – they do not necessarily carry the same connotations. For this reason, there is not a perfect coincidence between levels of different classifications and some of them are not well defined. In addition, US classifications tend to mainly cover the design and construction phases and focus to a lesser degree on the operation, management and maintenance phase.