Thursday, May 23, 2013

The End to CADdiction?


At the end of its design development phase, a current project hangs in the balance between CAD and BIM. This study was commenced in an attempt to influence the direction of that decision. 

The "GA" Apartment project was earmarked as a possible Revit/BIM project several weeks ago. Because of its impending launch into the CD phase, it was important to formulate and test the intended methodology for the accomplishment of that task using Revit.

A breakthrough concept that has evolved over the last several projects is the understanding that the highest efficiency can be gained by modeling the largest repeatable segment of the building. On this type of project, it is the entire "stack" of units of the same type.

A review of the project reveals that there are only six distinct unit types, and that these unit stacks occur in 2, 3, 4 and 5 story configurations. The interior of the units are identical on every level, while the building exterior envelope may vary based on story level and interior or end condition.


A variable height mass component family was created for each unit type. This is simply the unit footprint, extruded vertically. Each family is color-coded. When placed in a massing model, these height of these components may be varied parametrically. A complete massing model may be quickly assembled by placing these 3D families, and filling in the interstitial spaces for circulation and other services.


These components, of course, contain basic area and volume data which may be scheduled. Over time, a library of the many variations that are generated during design will be assembled, reducing repetition and further accelerating the project development process.

The next step in bringing the project to life involves the creation of the stacked unit model. For this exercise the most typical unit type was selected. The mass family is loaded into a separate project file. Walls, floors, and roofs are created by selecting the faces of the massing model. Next, doors, windows, decks and railings are added. Objects that repeat from level to level are grouped for consistency and efficiency. Roof slope is assigned and parapet walls are extended vertically. Finally exterior materials are specified.


These refined stacked unit models replace the massing families in the composite building model. Variations may be depicted using design options.


For the building site model, existing topographic data was imported into Revit. The topo surface model is created automatically. Revit’s phasing feature allows refinements of the model, and reports approximate cut and fill quantities.



There is no debate about the value of Building Information Modeling. That has been realized for many years by countless practitioners on projects of all types. BIM is the obvious choice for design and construction professionals whose goals include the delivery of accurate and well coordinated contract documents. This can, of course, be achieved with the current system, but only with a high degree of discipline involving knowledge that has nothing to do with architecture. BIM assigns that responsibility to the software program, and allows users to focus on their specialty, whether it be management, design, or production. A small percentage of owners and builders now require BIM, but its benefits accrue to every project stakeholder, regardless of their level of knowledge or participation.

BIM can be used solely for production, but the maximum benefit comes from moving its application "upstream". For most homebuilding architects, the design work flow involves Sketchup and CAD. The main flaws of this methodology are that the models are hollow and contain no volumetric data; secondly, it (again) requires great discipline to keep the two programs in sync, until the goal is eventually abandoned.

The mass modeling capability of Revit is equal to Sketchup, and in the process described here, leads to a rapid and efficient development process, and an accumulation of resources which are easily accessible across all studios, offices, and project types.





1 comment:

  1. For those who read French, here is a good explanation of BIM - IFC : http://www.rhino4you.com/1/bim_ifc_maquette_3d_383350.html, and what the French call the digital model/sketchup/mockup (maquette numérique).

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