Recently I was spending some time developing a very detailed curtain wall system with Archicad. The objective was to have an exact virtual representation of the real curtain wall construction system with all profiles, membranes, sealing, screws, etc.. The request came from one of our Graphisoft Partners in the ESEA region. They are working with a user that wanted to see an Archicad model sample developed at “LOD500”, as the user quoted. And here comes the problem: The “LOD” term. Why professionals of AEC/O industry keep using an outdated and often misleading definitions as LOD when describing how detail a model should be? But most importantly, what do they think LOD means and what do they expect from it?
Don’t get me wrong, Archicad is a fantastic tool to develop very detailed models for construction, pre-construction and facility management. The capacity of Archicad of handling complex and heavy models is by far superior to other popular BIM solutions (ring a bell?)… The problem is that this LOD (Level of Detail) it is not by itself a true standard of how in detail we should model the geometry of a construction assembly, but more like a compendium of guidelines that belong to a larger set of specifications. There are many standards that use the term LOD in many different ways.
This is why a wrong understanding of LOD attributed to “a whole model” has misled a large amount of AEC/O practitioners. Some of them have been very keen in highlighting how good quality models they have developed following “this or that LOD”. But what does it actually mean? Finally and also thanks to the ISO19650, the elephant on the room was pointed out when these set of documents highlighted that there is not such a thing as Level of Detail (LOD) for a model, but Level of Information Needed (LOIN) for an element.
There are many guidelines that mention LOD attributing different meanings to it. Some countries have developed their own set of standards for the use of BIM. If we have a look to the PAS1192 from UK, This document briefly mentions “Level of Detail” as such. It elaborates more on the idea of Level of Model Definition. There are 7 stages and different instructions for each purpose. As we can read at the different stages of the below table, there is not a clear instruction on the Geometric Detail Level. But even more emphasis on information.
Another example is how LOD is referred on the AIA (AIA G202-2013). The reference to LOD in this document also specifies that at different stages of the project, a model could contain elements with different Levels of Development. Making it clear that there is not such a thing as “a model at a specific LOD”.
And how much information shall we add to an element? Does any of these definitions of LOD describes it? As we have learned over the years, Information is the most important thing when it coms to use BIM technology and process. We should be talking about the Level of Information rather the level of geometrical definition when it comes to requirements for our projects.
Let’s put the example of an “as-built model”. What is the purpose of it? Shall it be a detailed 1 to 1 representation of the real element? On the case of an as-built model we just need a virtual model that represents the building status as it is built. The information of this element is more relevant than its geometrical development. The level of geometric detail should be as detailed as needed for the owner to operate the building from now on. Any equipment system should have all information needed to be operated, maintained, replaced, etc.. Does for this purpose help in any way have a super detailed and heavy 3D representation of it? Probably not.
Very often these highly detailed models are not “capable” of providing documentation needed for the project. Documentation needs to be generated along the Design stage when designing a project. Another advantage of BIM is that we can automate most of the documentation and information from our model. It doesn’t matter how detailed a model is, if we need to develop several models of the same project to provide different type of documentations, we are duplicating tasks and losing efficiency.
BIM consultants often are hired to develop these “additional models”. When a design team like Architects or Engineers, try to implement BIM in their projects, if the tool they chose do not allow them to design at the same time that they need to produce, then they need someone else to “do BIM for them”. Weather is an additional “BIM department” or a BIM Consultant, we are constrain to duplicate. The trap of duplication of work is what most design teams “Authors” are constrain when trying to use wrong “measurement references” such as Level of Detail.
The Conclusion is that in some cases companies have unfortunately invested lot of resources, time and money to develop half way useful models due to wrong guidelines and assumptions. Investing in additional personnel and powerful workstations to develop very detailed models for coordination purposes, using some BIM solutions unable to handle them in some cases.
That is why, we need to truly understand the outcome of what we want to achieve when we use any technology. Only then we will be able to leverage on it.
