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What is LOD? How it Impacts Project Delivery on BIM

June 9, 2021

Building Information Modelling

Building Information Modelling (BIM) is part of most public/private construction projects in India. But most (almost all) BIM projects get into a Level of Detail (LOD) debate in the midway and stakeholders lose the vision(essence)of the project which brought everyone together in the first place.

Eventually due to project delivery pressure keeps the BIM parallel to the project's delivery timeline and moves back to tried & tested 2Dbased project delivery.

It needs to be clarified that this experience is in the project ecosystems which we know and hear about. So, without generalization let us try to understand this LOD debate from all sides:

Before getting into discussion let us define few terminologies in the context:

1. What is BIM? Building information modeling (BIM) is a process of using “information enriched 3Dmodels” throughout the “building life cycle” by leveraging different “tools/technologies”.

2. Building life cycle: Design –Construction – Operations – Refurbishment/Demolition is noted as building lifecycle basically building’s inception to the end.

3. Information in 3D Model: When we say information, it might be

a.  Geometric (Visual) Information: representing object's physical shape & size.

b. Non-geometric information: representing the object’s technical properties.

Example 01: Door

·       Geometric information: Width of the door, Height of the door, the thickness of the door, its actual color, finish, etc.

·       Non-geometric Information: Fire rating of the door, weight, cost code, manufacturer, etc.

Example 02: Air Handling Unit(AHU)

·       AHU’s Length, Width, Height, etc are its geometric information.

·       AHU’s airflow rate, fan capacity, Coil dewpoint are to be categorized as non-geometric information.

4.  Tools/Technologies: While working on the BIM process many software are put into use rather than just one. This is a particularly important understanding as in multiple instances project environment specifies the use of 1 tool for all use cases. Popularly know technologies are illustrated for better understanding.

a.  3D Model Authoring: Revit, Archi CAD, Tekla, Vector works, etc.

b.  Collaboration Tools: Navisworks, Solibri, etc

c.  Quantification & cost management: Costx, Nova 5D BIM etc

d.  Construction Sequencing or 4D: Navisworks, Synchro, etc

e.  Operation using CMMS: Granlund manager, Maximo, etc.

LOD: Level of Detail (LOD) popularly refers to the representation of geometric information represented in a 3D model.

Generally, in projects representation is like LOD 100, LOD200, 300, etc LOD 500. Where LOD 100 means the model has lower geometric information compared to LOD 200.

So now that we have understood few terminologies let us get back to our discussion of LOD. In developing an “Information enriched 3DModel” time is spent in 2 activities:

·       Developing Geometric Information

·       Enriching Non-geometric Information (also referred to as Level of Information need (LOI))

So let us derive an understanding that the time consumed for 3Dmodelling is proportional to the level of detail (geometric & non-geometric) requested in the project.

BIM specification document must clearly specify what is the expected details with reference to geometric information & non-geometric information in the 3D Models (BIM).

Naturally, the question comes what LOD should be specified: Mostly it is the psychology of “Bigger the better”. So, most BIM specification document request for BIM up to LOD 500. But let us put a step back and try to understand what LOD one should specify/request from the design team.

Broad explanation of LOD as per BIM Forum 2019:

Broad explanation of LOD as per BIM Forum 2019, image

Before specifying the LOD requirement of the project we need to identify the use cases of BIM. Though the BIM technology can enable hundreds of use cases, the project team needs to decide the use cases identified for the project.

Let us understand how the use case identified for the project influences the information in 3D models.

Guide to read the table: Here use cases identified for the project are mentioned and associated understanding to develop a model in terms of geometric & non-geometric information is also noted. A comment is an additional layer of notes for the benefit of the reader.

LOD & BIM use cases explanation, image

Summary of the discussion

1. 3D models can be extremely detailed in terms of how they look visually. But the development should be in the interest time & cost restricted to use case. This exercise should not be to test the organization's capability or software rendering capabilities.

2. Not all elements modeling is required in 3D to develop a detailed quantity. A specialized software environment can enable for formula-based extrapolation. This will avoid modeling time-consuming to less useful elements into 3D models.

3. Owner organization should clearly specify the use cases project in the bidding stage to understand the expectations.

4.  LOD alone cannot give a clear understanding of information to be modeled into a 3D model. LOD specification should be coupled with the specification of use cases & Level of Information need (non-geometric).

5. LOD 500 might necessarily not mean that is a more detailed 3D model in comparison with LOD 400.

6. Implementing standards like ISO 19650 into the project and referring to documents like the BIM forum for LOD requirements will bring better standardization in terms of delivery expectations in projects. But BIM specification document should suit each project and organization’s diverse requirement.

7. It is strongly advisable that a qualified subject matter expert organization is engaged specifically so that they can clearly understand the project vision from owner representatives in plain language and then translate it into a good BIM requirement document.

LOD debate is valid but the has no end unless we understand the rationale as construction projects are complex with hundreds of stakeholders having their own challenges of delivery. We at Desapex aim to use fewer terminologies and bring more relevance to use cases identified for the project to make BIM work in the interest of the project.

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