Week 4 - BIM vs. Drafting (with a CAD Program) - Advantages and Disadvantages

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

As many companies merge towards incorporating BIM into most of their projects, they may wonder if using BIM has more advantages than disadvantages.  The easy answer to this question would be that BIM is much more advantageous due to its ability to perform parametric modeling and incorporate all of the different systems within a building at once.  For example, Dongyan Qi described in his blog post about BIM being able to provide a 3D walkthrough and renderings of all of the systems.  However, BIM does more than just this.  Unlike BIM, CAD is a 2D technology that outputs a collection of lines and text on a page. These lines have no inherent meaning, whether inside the computer or on the printed sheet. . . there is little to no correlation or intelligent connection among them.” (Dzambazova)  If two parallel lines are drawn in CAD, they say nothing about that wall other than it exists.  It does not give the materials that make it or any of the material properties.  BIM, on the other hand, is modeled so that “Each component and material understands its physical properties as well as how it will perform as a building system so we can get rich data out of the model regarding heating and cooling, most efficient building orientation, solar gains, etc.; we can test our building before it’s built” (Webster)  The objects are no longer modeled as just a set of lines that give the dimensions, they can be specified “in terms of its structural, acoustic, thermal or aesthetic performance. “ (Hamil)  Engineers can use this info, which can be updated if necessary, to determine things like how the combined insulation properties of external and internal walls affects the heating and cooling loads that will need to be provided by the HVAC in the building. 

As convenient as it is to be able to monitor and produce models that can provide these properties, it can have some drawbacks as well.  For example, CAD can be seen as being advantageous because it provides “a set of instructions for the intended means of constructing the building. Exact means in this method are hashed out during shop drawings, coordination meetings and often in the field after construction has begun.” (Webster) This allows engineers using a CAD system to speed up the process of erecting a structure.  Many owners of the structure being designed would love to start the construction process as soon as possible, especially if they know that decisions can still be successfully made regarding the design after they have broken ground.  Also, there are many custom made materials and parts that are not included in the libraries of BIM software of objects to be modeled.  Matt Morimoto mentioned in his blog post about conduit elbows sometimes not being able to be connected due to sizing issues.  Although BIM software such as Revit allows the creation of families to model and place new 3D objects, it is sometimes only necessary, and therefore easier, to just provide a simple 2D model that can be easily created in a CAD system.  

Resources:

Dave Webster. "Keys to a Successful BIM Implementation: BIM vs. CAD: Really…What’s the Difference?" MasterGraphics Weblog RSS. N.p., 26 Oct. 2011. Web. 28 Jan. 2014. <http://www.mastergraphics.com/wordpress/2011/keys-to-a-successful-bim-implementation-bim-vs-cad-reallywhats-the-difference/>.

Dzambazova, Tatjana, Eddy Krygiel, and Greg Demchak. "Understanding BIM." Introducing Revit Architecture 2010: BIM for Beginners. Indianapolis, IN: Wiley Pub., 2009. N. pag. Safari. Web. 28 Jan. 2014. <http://my.safaribooksonline.com/book/cad/9780470473559/understanding-bim/how_bim_is_different_from_cad>.

Stephen Hamil. "Isn't BIM Just 3D CAD?" Nbs, Aug. 2011. Web. 28 Jan. 2014. <http://www.thenbs.com/topics/bim/articles/isntBimJust3Dcad.asp>.