Early Level-of-Detail Transitions to BIM Level-of-Development

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Wednesday, March 25th, 2015
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In the 1980s, the firms I served used Level-of-Detail (LOD) Standards to define both hand-drawn and CAD-created construction documents.

Serving as a draftsman, jobcaptain, CAD Manager and then transitioning to a CAD implementation consultant, I used and authored LOD standards for hundreds of my client firms.

Perhaps if you created hand-drawings or CAD-drawings, your manager may have voiced their concern at the Level-of-Detail you were incorporating into your views, saying things like:

  1. You’re showing too much detail in that 3/16” scaled-view.
  2. A CAD dimension with a 1/64” value? We don’t even build to that level of detail!
  3. Don’t add hatching in that 1/8” Section. Hatching detail is for larger-scaled views

Granted, early standards may have been designated as Graphic Standards or CAD Standards. However, these early Level-of-Detail Standards served three goals:

  1. Produce graphically consistent and well-coordinated documentation.
  2. Reduce the time to manage the inevitable document revisions and respective reference tags.
  3. Provide documentation that appeared as if one person had created the documents.

    architect_scale

Hand-drawn LOD Standards clearly defined and sought to achieve standard line weight widths and hatch graphics; quantity of content in each scaled view-type; dimension styles and text fonts and heights; view hierarchy and scale for key plan, plans and enlarged plans; and view hierarchy and scale for building sections, wall sections and details.

Our guide for defining our Level-of-Detail was our manual measuring tool, the architect’s scale.

As the views’ drawing-scale increased, more information (detail) was included. Standard LOD guidelines worked to minimise redundant information between manually drawn views.

For example, door and room tags were placed only on the 1/8” plans. They were not placed on the 1/4” or 1/2” enlarged plans. If a door or room number changed, we only needed to manually change the door and room tag values on the 1/8” plan sheets.

Door Cad Detail

Door CAD detail

CAD-created construction documents expanded the use of hand-drawn LOD throughout the 80s, 90s and into the new century. CAD and printing technologies provided better tools that further redefined the CAD LOD definition and functionality.

Initially, CAD LOD served and remained dependent on the manual measurement of scaled paper documents. However, as the CAD process evolved, firms avoided the printing process and began the dimensional-checking of construction drawings using their CAD software for length, width, height and angles.

The newer CAD LOD redefined the minimum project units for associative-dimension values to 1/8” or 1/16”. This helped designers to validate projects’ dimensional constructability in the CAD software much sooner and more often during the project design cycle.

For example, nominal wall styles (five-inch drywall or eight-inch block) were drawn as their actual size (4-5/8” drywall or 7-5/8” block). CAD LOD standards set a threshold of detail for each view type. There were diminishing returns if we created too much detail; which consumed additional project billable time.

The CAD layering process delivered smaller line-widths via high resolution plotters and printers. This provided a variety (options) for more detailed documentation in hi-resolution color, using halftone (screening) of architectural-engineering coordination plans, and featuring gray-tone (shades-of-gray) while using various lineweights.

As CAD software ‘Layout Pages’ became the dominant printing tool; the LOD for Model Space was increased. Model Space now served as the data host for multiple Layout Pages within a single CAD file.

Higher quality printing at smaller scales reduced CAD annotation sizes while improving legibility throughout the documentation. Firms began moving details and text content from Details and Specifications Manuals to sheets within the document set.

Level-of-Detail (LOD) continued to evolve with both 2D and 3D CAD software improvements. However, once BIM software and processes gained serious momentum, Level-of-Development provided a better functional definition.

The second installment in this series, BIM Level-of-Development (LOD) Driving BIM ROI, will expand this new LOD definition as it will share how LOD is evolving toward improving BIM project management, establishing goals that align project BIM deliverables that are closer to the owners’ BIM strategy, and integrating the team members’ independent LOD standards with the projects’ LOD standards.

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