Helping BIM and RIBA make a LOD
of sense

It's important to realise that BIM isn't a silver bullet for every design and construction project. The detail that can be achieved within BIM is entirely dependent upon the information available from the initial design. That's why it's essential for all parties to understand and agree what level they are working to from the outset - and, critically, what can be achieved or extracted from each level.

I can best illustrate this with a recent example (and there have been several) whereby I was asked by a contractor to provide the fee proposal to produce a full bill of quantities based on their BIM model. A fair question, until I looked further and discovered that their model was only complete to LOD 200 (see more about LOD below).

Now, although LOD 200 is a perfectly valid BIM level, the resulting bill of quantities delivered by our BIM system alone would not be of the same standard and completeness as it would for a model that has been fully designed - nor would it have been to the level that the contractor was expecting. At the moment we understand that this is frequently the case and apply our knowledge and experience to accommodate missing elements within the design and drawings and thus fill many (but not all) of the gaps.

However, as we collectively move towards the more integrated use of BIM across the industry, this relatively high level of 'manual' interpretation will diminish, as it should, but in turn it will mean that the quality of any output will be more directly linked to the quality of the initial model. The benefit will be a more rapid, dynamic and in time cost-effective process but it does mean that we all need to realise that the level of benefit and cost-saving we achieve will be directly linked to the detail and accuracy that we have at the beginning of each project. Yes, we can still correct or add detail at any stage (and the ability to do this within a live model is one of the advantages of BIM) but we need to set the right expectations amongst ourselves and with our clients to ensure that everyone knows just what can be achieved from the data contained in the model that they supply. BIM is a powerful tool, but like all software it can only work with the information it contains.

This lack of clarity is not surprising given the different and frequently conflicting discussions regarding BIM, but it's something we will all have to work carefully to avoid in future. To help bring clarity it's worth spending some time looking at the distinct levels of model and information detail within BIM, called Levels of Development (LOD). These help define consistent expectations throughout the building life-cycle from planning through design and construction, but introduce increasing detail at each stage, with the initial level only providing the conceptual design through to LOD 500 where we can start to establish a program for the life-cycle management of the building.So you can see that a model designed to a specific level, for example, LOD 200, whilst perfect to provide an indication of the building's functionality and budget, does not contain enough information to create a comprehensive bill of quantities.

Each of these LODs maps to a RIBA work stage and although there isn't room to explain it in this email you can download a full explanation by clicking here.

Each Level of Development is generally defined as follows:

LOD 100 - The equivalent of conceptual design, the LOD 100 model usually consists of overall building massing designed to perform whole building type analysis including volume, building orientation, square foot costs, etc.

LOD 200 - Similar to schematic design or design development, the model would consist of generalised systems including approximate quantities, size, shape, location and orientation. LOD 200 models are typically used for analysis of defined systems and general performance objectives.

LOD 300 - Model elements equivalent to traditional construction documents and shop drawings. LOD 300 models are well suited for estimating as well as construction coordination for clash detection, scheduling, and visualisation. LOD models should include the attributes and parameters defined by the owner in the BIM deliverable standard.

LOD 400 - This level of development is considered to be suitable for fabrication and assembly. This LOD is most likely to be used by specialty trade contractors and fabricators to build and fabricate project components including MEP systems.

LOD 500 - The final level of development represents the project as it has been constructed including as-built conditions. The model is configured to be the central data storage for integration into building maintenance and operations systems. LOD 500 models will include completed parameters and attributes specified in the owners BIM deliverable specification.

Although this is a relatively simple exercise in ensuring that the final output is defined at the start to ensure we have sufficient data to build an appropriate model, I think there has been a lack of clarity until now with a tendency for the term BIM to be used simply to represent any 3D modelling process. In the early days that was fine - BIM was a distant thought on the horizon of our profession. But today, as BIM becomes a reality, we need to be confident that we're all talking the same language or, like the ancient builders of the Tower of Babel, we might end up with a result that falls far short of our expectations!