To model or not to model: That is the question.

November 17, 2010

There was much talk at last night’s meeting about how much modeling should be done in a BIM project.  Revit will let you model everything. That can become a pitfall for most new users. That type of creation consumes a vast amount of time and ultimately slows down your model.

The AEC (UK) BIM Standard for Revit, on page 27, Section 7.2.1, offers some good advice and a visual to help with this particular issue.

At the outset of the project, consideration shall be given to the maximum level of detail to be included in the BIM. Too little and the information will not be fit for purpose; too much and the model may become unmanageable and inefficient.

  • The BIM Co-ordinator shall dictate the point at which 3D geometry ceases and 2D detailing is utilised to prepare the published output.
  • Intelligent 2D linework shall be developed to accompany the geometry and enhance the required views without undue strain on the hardware. 2D linework is not exclusive to detailed/fabrication information.
  • Detailing and enhancement techniques shall be used whenever possible to reduce model complexity, but without compromising the integrity of the model.

3D modelling is carried out to an accuracy of approximately 1:50

…so imagine the level of detail needed for a physical 1/4 inch scale model.

As discussed last night, the different disciplines have different needs. Sometimes that level of modelling detail must be there in order to reap the benefits of using BIM.

Using BIM demands an open line of  communication. So  before going into the modeling portion of the project, have the team discuss what families are needed. If they are needed, to what level of detail do they need to communicate design intent. Do they need a lot of fancy parameters? There needs to be a ‘stay on task’ conversation to make sure the project is focused on the end result.

I’m sure as more usable family content becomes available, the hardware gets beefier and the sharing of models becomes more routine, this issue may go away. Until then…To model or not to model: That is the question.

One comment

  1. Kirk, you are correct. Deliverables and communication are key. To sell services in a competitive environment and still be profitable demands clarity. The AIA document E202: http://www.pat.ca/files/pdfs/AIA_091708_E202-2008_eSample_Blank.pdf tries to define Level Of Development (LOD 100-500)) for projects. Alternatively Consensus DOCS 301 cites a BIM Execution Plan which helps define the level of development / detail and deliverables for projects. PENN State (http://www.engr.psu.edu/ae/cic/bimex/download.aspx) and other have started to block out a framework to help define these things.

    For Team BIM projects I am of the opinion that a BIM execution Plan is absolutely required. Additionally clearly defined modeling levels and maybe even prototypes are required so team members have a clearly defined reference.

    Once defined we have a known quantity of services that can be sold and produced.

    After contract obligations have been met Teams may wish to take things further (read: over model or input “I”nformation) for any number aspects to improve efficiency. Cost estimation, Specifications, QTO, Fabrication, shop drawings, field coordination, analysis, etc.

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