3D BIM Modeling - Level of Detail and Model Progression Specification

April 10, 2017 Doug Elliott

Three-dimensional modeling (aka 3D modeling services) is becoming more common in today’s construction processes, with 3D BIM modeling services seeing especially fast adoption. While models are easy to create, the question remains, what is the 3D model good for? Is it just a pretty picture or can it actually be fabricated and constructed? To help answer those questions, we will explore Level of Detail (LOD) and how it impacts modern building information modeling.

Background

Building Information Modeling (BIM) requires input from the different stakeholders in a project. As the project progresses, more and more detail can be added to the model as it develops from conceptual to constructible.

In the past, when you received a model, it typically came with a disclaimer from the architect that the model was NOT to be used for construction and was for reference only. This problem was stated very humorously and succinctly at a recent AGC BIMForum.

“This model looks great so you can look at it, but you can’t use it for anything or rely on it for anything, which includes, but is not limited to, everything.

If you use it for anything anyway, then you have to pay my lawyers anything they want if I get sued for anything related to your use of the model for anything.

Have a nice day.” – Jim Bedrick and James Vandezande

In 2008 the American Institute of Architects (AIA) released the E202–2008 BIM Protocol. This protocol helped define what a model could be used for by creating a model progression specification, and what type of information could be derived from each progression or what you could trust the model for.

This has been adopted by the AGC BIMForum as well and much of the work that lead to the E2O2 docs came from work done by Vico Software (which is now a part of Trimble). This year there was an update to the protocol; AIA Document G202-2013 – Project Building Information Model Protocol.

What is LOD?

LOD has been referred to as Level of Development and Level of Detail, either acronym is acceptable. Here are the different LOD definitions for the AIA E202-2008/G202-2013 BIM Protocols

100 Conceptual

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.

Approved uses: Analysis, cost estimating and scheduling

200 Generic Placeholders

 

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.

Approved uses: Analysis, cost estimating and scheduling

300 Specific Assemblies

The Model Element is graphically represented within the Model as a specific system, object or assembly accurate in terms of quantity, size, shape, location, and orientation. Non-graphic information may also be attached to the Model Element.

Approved uses: Construction, analysis, cost estimating and scheduling

400 Detailed Assemblies

The Model Element is graphically represented within the Model as a specific system, object or assembly that is accurate 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

Approved uses: Construction, analysis, cost estimating and scheduling

500 As Built

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

 

The pictures below illustrate the model progression specification as well as subtle differences between progressions. While a model may not be fully LOD 400, it may qualify for LOD 350 (or halfway between 300 and 400). In the example, more detailed assemblies, detailed pipe insulation, as well as more detailed pipe routing qualified it for LOD 350.

Level Of Detail

3D BIM Software Images Courtesy of Trimble MEP Services Group

Limitations

Now that we have discussed what LOD is, let’s cover the limitations.

There is no such thing as a “LOD 400” federated model. A federated model is the combination of all the different trades into one model. The electrical may be LOD 300, the mechanical may be LOD 350 and the HVAC may be LOD 400. All of these are at different model progressions.

Different LOD need to be reached for a certain trade before the model can be constructed in the field. For example, LOD 300 for electrical is acceptable for construction as most of the parts are purchased. For HVAC ductwork that is fabricated, LOD 400 must be achieved. Each level of progression takes more time and adds more cost to the project.

Conclusion

Each LOD phase requires more specialized technology as well as increased skillsets to properly address the finite details within the 3D BIM model.  

Field tools, like the Trimble Robotic Total Station, can be used around LOD 300 when specific assemblies are indicated in the model. This applies to walls as well as MEP equipment, ductwork, conduits and cable tray. Electrical estimation and mechanical estimation duties may well require LOD levels that are different from what is required at other stages of the BIM process, as is the case with each step along the way.

The E202-2008/G202-2013 protocols have, however, allowed more open collaboration between project stakeholders. As a result, if the author can clearly state what the model will be used for, then the consumer of that model understands what to expect. And that’s a huge step toward more effective and efficient BIM collaboration.

At Trimble, we understand the complexities inherent in deploying technology and training personnel to keep pace with these demands. Should you have questions or need assistance on a current or a future project, please visit our BIM Consulting Service web page or call one of our Trimble MEP 3D Consulting Services representatives at 1-800-234-3758.

About the Author

Doug Elliott

Doug is a Software Product Manager at Trimble MEP.

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