All models are purpose-built, even when they’re not

The reality is that most models out in the wild today are built for one purpose: documentation. Yes, there are plenty of examples of models built for other reasons, but let’s just say the vast majority are out there trying to meet deadlines and if they have to throw in some drafting then so be it. In this case then, documentation was the intended use for the model, regardless of what your friendly neighborhood marketing department tells the rest of us.

Along the path of pointing out things that cause friction with design technology processes, mis-understanding the concept behind purpose built models is high up on the list. A purpose-built model is one that is built with an intended use (or uses) in mind. An example of an intended use may be something like ‘fabrication’, ‘documentation’, ‘engineering analysis’, ‘coordination’, and many others. The key consideration then, is that each of these uses requires slightly different geometry and / or model information.

Defining the intended use of the model gives clear direction to other users. Together with a defined level of granularity, or resolution, it is a powerful tool in understanding what information should and should not be in it. For this reason, many of the more thorough BIM specifications or BEP templates publicly available make reference to model uses.

The newly published New York Department of Design and Construction’s BIM Guidelines lists the following intended uses for their projects:

  1. Existing Conditions Modeling
  2. Site Analysis
  3. Programming
  4. Engineering Analysis
  5. Design Authoring
  6. Sustainability (LEED) Evaluation
  7. Design Review
  8. Code Validation
  9. Clash Detection
  10. Cost Estimation
  11. Construction System Design
  12. Phase Planning
  13. Digital Fabrication
  14. Record Modeling
  15. Asset Management

The VA, on the other hand, calls them ‘BIM Applications‘ and lists the following as a minimum:

  1. Space and Medical Equipment Validation
  2. Architecture – Spatial and Material Design Models
  3. Energy Analysis
  4. Design Visualization for Communication, Functional Analysis, and Constructability
  5. Building System Models – Sturctural, MEPF, and Interiors
  6. Masterplan Space Scheduling and Sequencing – 4D
  7. Communication of Construction Scheduling and Sequencing – 4D
  8. COBIE / Commissioning
  9. Clash Detection / Coordination
  10. Virtual Testing and Balancing

The GSA goes even further and has released individual guides for each of their sought after uses:

  1. Spatial Program Validation
  2. 3D Laser Scanning
  3. 4D Phasing
  4. Energy Performance and Operations
  5. Circulation and Security Validation
  6. Building Elements
  7. Facility Management

Some of these may seem a bit vague, but they all intend to direct a particular end use for a model. Each of these describes how the model will be used for each task, and what information should be included in the model in order to achieve said task. Notice how three large ‘owners’ that require BIM processes all are focusing on distinctly different things. They each care about different aspects of their facilities more. Be it security concerns for the GSA, equipment management for VA, or energy analysis for the DDC, each has implemented a process and frameworks to support their end goals. I’d like to hear how these are performing in real life…

In any case, this advice is not only for those consuming BIM. Those authoring and promising BIM to downstream users would do well to explain exactly what the model was built for. This will help frame expectations for the next user in line and many of the frustrations or mis-aligned expectations about what should or should not be in the model will be minimized.