There is no such thing as a LOD 300 Model!

You either understand the statement and maybe even disagree, or the first thing you are asking yourself is what is an LOD.  Either way, this is an important concept and I will explain and prove the point. 

Sharing model information is a necessity in the value proposition of BIM. And setting expectations about the use and reliance of that information is the only way to protect yourself and your firm from unintended consequences and the associated risks.  Understanding the development of a model throughout its lifecycle is essential to your success and explaining that to all the parties in a project is a common vocabulary we all must all share.

The first piece of information is the concept of an LOD, aka Level of Development.  First associated with the model progression specification developed by the AIA California Council, it was often called Level of Detail.  But Level of Detail is more often associated with the graphic fidelity of a model in the gaming and rendering industries. Even BIM associates this concept with how much detail is visually displayed, which is totally different than todays evolved concept of Level of Development.  In today's usage it is at the core of the AIA's BIM protocol agreement, the E202, which helps establish the foundation of sharing BIM information.  Simply stated LOD is the level to which a Model Element is developed and can be replied upon in the design and virtual construction workflow of BIM. 

Each Model Element is a subset of the virtual building in BIM, divided by CSI level 300.  For example, exterior walls, interior walls, and ( finish) are all different Model Elements defined in the E202 matrix.  Each LOD rating; 100, 200, 300, 400 and 500 are different levels of a Model Element's development, and each LOD defines the usage rights including to what extent that Model Element can be relied on.  Each LOD is not necessarily a linear progression on the one before it.  LOD 500, for example is the verified model for use by the Owner and is generally post construction.  A LOD 500 element might be used only for operations and maintenance and have only bounding box geometry, with only information suitable for repair and maintenance. LOD 500 is often the most misunderstood LOD, because of it could be a discreet subset of the information that came before if the Model Element was developed to a level 400.    An example might be structural concrete, which at LOD 400 includes rebar and other shop drawing and fabrication level information, which cannot easily be post construction verified and serves no real purpose to an owner for O & M. It would simply be useless information that slowed model visualization.

In the matrix of the E202, each Model Element is developed to the level appropriate for the milestone indicated. For example, I would typically model an elevator to LOD 100 during Schematic Design by only showing a rectangle and a symbol on the plan; to LOD 200 during Design Development, by showing the cab size, door opening pattern and the overrun and pit in the sections; and LOD 300 for construction documents by showing, hoist and guide rail locations, and fully articulating the design intent using a specific elevator companies design information.   If we were working in an integrated project, the contractor and sub would further develop the model element to LOD 400 as they laid out all the details for fabrication and erection. And regardless of the delivery method, an LOD 500 might be developed, which verified the installed elevator manufacturer, and incorporated lubrication and inspection data along with parts lists, but no longer included information on hydraulic piston shaft reinforcing requirements, or can assembly instructions. 

The confusion starts when people assume that all the Model Elements are developed to the same level at each milestone.  All Model Elements are not LOD 300 for construction documents, nor are they all LOD 500 for a record model.  Each Model Element generally develops independently of the others, so they are never at the same state of development.  This is also true because some Model Elements never develop to greater levels, for example finishes which are indicated in a schedule but not generally modeled beyond LOD 100 or some parts to LOD 200.  

Generally you may have a set of BIM supported contract documents made up of Model Elements that are at LOD 100, 200 and 300, including some that might be annotated as "In the project, but not modeled".  So remember, LODs apply to Model Elements not the overall models, and that all of the E202 matrix is subject to your agreement with the rest of the team.   It is a working document, and intended as a tool to facilitate sharing.  We will cover it in greater detail in a separate Blog.  So get out there, but please practice safe BIM!

- Bob

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