BIM vs. Drafting (with a CAD Program) - Advantages and Disadvantages

In the 1980s most architects and engineers used drafting boards for drafting; then CAD applications revolutionized the AEC world. Now, most architects and engineers use CAD applications, and BIM is on its way to revolutionize. 

Both CAD and BIM are applicable for building modeling. CAD programs are great for simple geometry, as it draws as you would by hand – it makes 2D lines, circles, ellipses, rectangles etc. When you draw a line, a line appears. With BIM technology, drawing a line can create a whole wall. With BIM, the building is a digital database that holds information about the geometry of the components as well as the data relevant to these components. (5)

But which way is the best way to make a building model? Here are 5 rounds:

Presentation:  With BIM you create a virtual 3D model of a buildings, and sheets with sections and plans are automatically made directly from the model. With CAD programs you draw every plan, section and elevation manually. As BIM models are whole buildings, it is easier for clients to understand than a regular 2D plan or section. Not everyone can understand 2D CAD drawings, and more exciting architecture is possible, as the client can actually figure out the design.

Change management: With CAD programs every line has to be drawn manually, and if one thing changes, everything will have to be changed manually to fit. With BIM technology everything is connected, so changes made in one place will automatically change the whole model. 

Simulations: CAD programs only generate lines, which can’t be used for any simulations. BIM models contain data related to the different engineering disciplines such as the load-bearing structures, all the ducts and pipes and sustainability information.

Data: With BIM, schedules of necessary manpower, coordination, and building components can be created automatically, which improves the calculation of costs and quantities. With CAD everything will be measured and calculated manually, which means more manpower and can involve errors.

Building operation: BIM models contain so much data that can be used throughout the entire building lifecycle, helping to reduce the operation and management cost. 

CAD programs mimic the hand drafting process, and BIM technology simulates the real world. 2D drawing is still the preferred method, probably only because of tradition.
It is easier to start drawing with a 2D CAD program, and it takes a whole other workflow to start using BIM. But buildings aren’t just lines that represent something, buildings are real and should be computer-generated in that way.  

Comments: 
Jeremy: Really great post. One sentence stuck with me: "(…)These lines have no inherent meaning, whether inside the computer or on the printed sheet". I think that really says how outdated the regular 2D output is.

Andrew: I found your post very interesting, especially the last part of the architects only thinking of the near future and not the entire life time of the building. Hopefully in the future the architects and engineers can work close together and create beautiful and sustainable buildings - not just buildings that are sustainable with energy savings here and now, but also with a long life time.

Sources:

1) Gaidytë, Rita, 2D and 3D modeling comparison, Gjøvik University College, May 25^th 2010

2) Grabowski, Ralph; CAD & BIM: Is there a free pass? Whitepaper; a research paper from upFront.reSearch funded by Graphisoft; 2010

3) Graphisoft; Open BIM; http://www.graphisoft.com/archicad/open_bim/about_bim/

4) Hardin, Brad; Death of a CAD Draftsman; Constructech; http://www.constructech.com/news/articles/article.aspx?article_id=8572

5) Magdy, Ibrahim; To BIM or not to BIM, This is NOT the Question: How to Implement BIM Solutions in Large Design Firm Environments; Department of Architecture, Faculty of Engineering, Ain Shams University; http://www.iit.edu/~ibramag

6) Webster, Dave, Keys to a Successful BIM Implementation: BIM vs. CAD: Really…What’s the difference?, Mastergraphics 2011, http://www.mastergraphics.com/wordpress/2011/keys-to-a-successful-bim-implementation-bim-vs-cad-reallywhats-the-difference/