Level of Development (LOD)

The level of development or LOD is a means to define the required contents of a Building Information Model (BIM) to deliver on the various project deliverables at each stage of the project from concept through to post occupancy.

The below table outlines the typical stages of development for LOD
(Table 1 - NATSPEC BIM Paper: BIM and LOD).

Open

The problem with this metric is that a linear level of modelling detail does not align with producing and delivering on the actual project deliverables over the various stages of a project lifecycle.

This misconception often results in BIM being specified at too high level of development, and rendering it too costly or the model being so heavy with detail it becomes unusable.

The NATSPEC BIM LOD Paper clearly describes this misconception with the below diagram providing a good example:

Open

Open

A photorealistic image of a chair is selected purely for the purposes of a rendering. Even if detail information is associated with it, it is not assumed to be relevant at this stage.

A generic model of a chair is selected for the purposes of a furniture layout even though a decision about the actual chair has not been made yet. The important thing is the nominal floor space allowance it represents.

During documentation a simple placeholder that helps minimise model file sizes is selected. The chair may appear in schedules or be used for costing but is not expected to be used for ordering.

A chair with a specific manufacturer and model number is selected for ordering purposes.

The chair has a manufacturer, model number, supplier, serial number and date of purchase, but its image, EG: A photograph, may not necessarily be included in the model.

A much less appropriate and less ambiguous approach is to break the Level of Development down into 2 separate categories Level of Detail (LOD) and Level of Information (LOI).

At each stage of the project life cycle as appropriate to the applicable Plan of Work for each Element category an appropriate Level of Detail and Level of Information should be defined to deliver on the Project BIM requirements.

Table 2: Comparison of International Plans of Work

The Level of Detail is used to define at what level the 3D modelling aspects should be completed to and the required accuracy of that modelling. BIM Uses may include:

• 3D Coordination & Clash Detection

• Construction Sequencing (4D)

• Cost Estimation / Quantity Take-off (5D)

• Visualisation

• Solar / Energy Analysis, etc.

The Level of Information is used to define at what level the metadata aspects associated to the model are to be completed, such as what parameters to include and how to populate them.

• Structural Analysis

• Services Analysis

• Solar / Energy Analysis

• Cost Estimation / Quantity Take-off (5D)

• Asset & Facilities Management

The level of development for every project undertaken within Revit should be carefully considered before any work commences. Each project will have its own unique set of deliverables suited to the level of documentation required. It should never be considered that just because it is in Revit that everything should be 100% modelled with information appended either.  That said, with a quality library and efficient team the difference in effort to produce a lightweight LOD 200 model vs LOD 350 model can be minimal.

The Level of Development should be agreed upon for all elements and phases, and form part of the BIM Management Plan (BMP/BEP).  This will ensure that resources are optimised for the outputs required.  It is usually dictated by how the model will be used both during the design, construction and post occupancy phases.

For example, will it be used for:

• 3D Coordination / Clash Detection

• Construction Sequencing (4D)

• Cost Estimation / Quantity Take-off (5D)

• Visualisation (Renderings / Animations / Augmented Reality / Virtual Reality / Mixed Reality)

• People & Vehicle Flow Simulations

• Code Validation

• Safety Planning

• Structural Analysis

• Services Analysis

  • Fire

  • Fuel

  • Security

  • Electrical

  • Hydraulic

  • Mechanical

  • HVAC

• Lighting Analysis

• Solar / Energy Analysis

• Fabrication

• Field BIM

• Site Planning

• Space Planning

• As-Built verification

• Asset & Facilities Management

  • Sensor Integration / Digital Twin / Systems Analysis

Each of these uses all have their own specific requirements depending on the project phase and desired accuracies, as such it is important to discuss this as early in the project as possible with the client and project team.

Beyond the LOD & LOI, it is important to define the model element authors (MEA) for each element at each stage. That is, who is actually responsible for creating the modelled element or populating the data to the required level.

In some cases and project stages, elements may have a split MEA. For example, for a Structural Slab, the architect will inform the footprint/extent of the slab, but the structural engineer is responsible for it’s thickness, material and acceptable penetrations, beams etc.