What is the LOD? In the world of Building Information Modelling (BIM), LOD stands for Level of Detail or Level of Development. It is a term used to describe the precision of a model.
LOD vs LOD
Level of Detail: The way a model looks. The level of detail refers to the input of the model.
Example: Specific shapes and measurable location of steel pipes in a model.
Level of Development: The depth of thinking applied to the model. The level of development refers to the reliability of the model.
Example: Whether the pipes in a model have been engineered and the permanence of their placement.
By today’s standards, Level of Development is the common reference. It might help to consider the level of detail as a criteria of the level of development. The more that a component is developed then more detail is provided too.
Before we dive into the specifics, let’s first take a look at how LOD emerged.
A Brief LOD History
Level of Development (LOD) was published by the American Institute of Architects (AIA) in 2009 and then further developed by the American General Contractors (AGC) which has been steadily expanding the definition.
Working for a mechanical contractor as a Project Manager (PM) in South San Francisco back in the mid 90’s, I recall the early challenges of sharing drawing files with the architect and consulting engineer. During this time we had a collision of existing hand drawing, 2D processes, and CAD modelling. The owner of the site was a pharmaceutical company and ironically the new building we were contracted to coordinate and install the plumbing was called “Building 3 D” a Bio Lab that would later be renamed.
Our contract scope included the lab gases and all plumbing. The multi-story building would have several floor penetrations due to the many lab sinks. The project specification called for stainless steel penetrations to be placed in the concrete slab prior to pour and all sleeves would need to extend above the slab 2 inches to prevent liquid spills from travelling from a top floor to a lower floor. Most plumbing penetrations are located in walls so simple 1+1=2. Locate the walls and overlay the plumbing and that is where the sleeves will be placed for the life of the building.
To begin our CAD coordination process, we requested the architect drawings and the consulting engineer’s drawings. We did not tell them what we wanted them for and they did not ask.
We began adding circles with varying sizes, for example, a 3-inch pipe penetration, which requires at least a 7-⅝ inch wall, and the circles did not fit in the thin double line walls provided by the architect. Much to my dismay, the architect and consulting engineer had not coordinated the vertical pipes, let alone the sleeves with the walls. I respond by writing a Request for Information (RFI) summary of which is “wall thickness WTF” and received a response along the lines of “We did not take the drawings to that level of development.” The drawings are issued for permit, all dimension shall be coordinated and verified in the field. Or summary response, the contractor is “SOL” – figure it out in the field like you always have.
This was a new conversation because paper blueprints do not provide this level of detail. During this same 90’s time period, I would be one of several people standing over a light table coordinating drawings. This method was the standard before Navisworks. The technology was a table that has a glass surface and a light that shined up so that two drawings would be lined up on the far left low corner and overlaid to see how each traded is in relationship to the others. We found that a CAD plotted drawing at say 1/8’=1’ overplayed with a drawing that was blueprinted would be several feet off when looking at the upper right side of the drawing. This is due to the moisture in the blueprint process that stretches the paper. This collision of existing processes and new technology created a much-needed discussion.
"How to maximize the benefits of CAD without changing the entire process or, worst yet, not providing the CAD files to the contractor at all?"
What the AIA did when it published the Level of Development (LOD) standards was set proper expectations of a drawing/model as they are shared with other stakeholders on a project. Fundamental to the heart of the dialogue of this simple truth. In general, the longer an architect and consulting engineer spend working on a model, the less profit the firm will realise. Conversely, the more time spent as a contractor working on a model, the more profit can be maximised.
As a contractor, we have seen architect and consulting engineers move from AutoCAD to Revit. But several MEP contractors are still in AutoCAD with workflows that are very proficient in their siloed process. Now that we have Level of Development (LOD) standards and we know what an MEP contractor can expect from the owner, architect and consulting engineers, the question becomes “What is the most efficient method of progressing a model from architect and consulting engineer LOD 200 to construction LOD 400?”
The first step is to share the Revit platform to leverage the LOD 200 design data and add the LOD 400 data as needed to prefabricate and install with BIM tools such as Robotic Total Station for sleeve placement and hangers.
Today architect and consulting engineer still provide standard walls with single line penetrations, the difference is that the construction stakeholders can schedule and estimate what is required as the model progresses from a design level LOD 200 to LOD 300, LOD 350 and LOD 400. The AGC provides a contractual structure for defining what LOD is required with a high level of definition.
LOD 200, 300, 350 and 400 – What’s the Difference?
But what is the LOD? It is common for people to still have a number of questions about the LOD and I am going to break down the basics for you.
- LOD 100 - A conceptual model that derives information from other model elements
- LOD 200 - Schematic setting out with approximate size, shape, and location
- LOD 300 - Modelled as design-specified size, shape, spacing, and location of equipment
- LOD 350 - Modelled as actual size, shape, spacing. Location and connections of equipment supplied
- LOD 400 - Supplementary components added to the model required for fabrication and field installation
As a contractor, you are likely bidding the project from a LOD 300 drawing or model. Virtual Design Construction (VDC) can be achieved at LOD 350, but profitability really happens at LOD 400. This is because LOD 400 allows for you to plan and even virtually practice how to fabricate and then later install each component. With LOD 400, you gain confidence in prefabrication, you are able to track completion of milestones with your scope and more importantly you are able to identify and document changes to your scope.
Achieving LOD 400 requires the right skillset, software and access to the right information. The most common mistake made by contractors is to use generic models which are high in detail, but lacking other relevant information. It’s not to say that this makes the job impossible, but using models from manufacturers or model sharing websites requires a lot of labour to add the development information that you need to support downstream processes. Trimble offers LOD 400 software products and the content you need. Additionally, Trimble’s MEP VDC Professional Services can support your 3D modelling and coordination requirements.
AOK on the LOD?
That’s the gist of LOD. It helps communicate the level of clarity and reliability of Building Information Models throughout different phases in the construction project. In short, the LOD helps define model deliverables, milestones, and handoffs.
Want to leverage LOD in your building information models but struggling to figure out where to begin? At Trimble, our professional services team understands it is increasingly more difficult keep up with changing technology, evolving industry standards, and rigorous project requirements while maintaining your firm’s profitability. Contact Trimble's VDC services team today to learn more about how our team of domain experts can partner with you – providing instant scalability to your organization and operating as an extension of your team, not just a subcontractor.
About the AuthorMore Content by Jim Reis