AEC From the Ground Up--Software Strategy: Building Modeling Options

31 Dec, 2004 By: AIA ,H. Edward Goldberg

How does BIM software stack up with the 3D model concept?

As software vendors push the BIM (building information modeling) concept, many firms are wondering how the various options stack up against the others. This article attempts to codify the distinctions among the major 3D building modeling applications. As outlined in the November issue of Cadalyst (, this genre of software uses the concept of working with components such as walls, doors and windows to create a virtual 3D building model from which views and information are extracted. The end result is the production of construction documents that resemble those created by 2D CAD or standard drafting methods, but these are created more quickly and contain information such as quantities, materials and areas that can be used in the construction and management of buildings.

The major BIM software products, in my opinion, are Bentley Architecture, Graphisoft ArchiCAD, VectorWorks ARCHITECT and Autodesk's Revit and Architectural Desktop. This conclusion is based on quantity of installed seats, true object CAD or parametric modeling capability, routines or programming dedicated to the architecture and construction industry and extraction of views and information directly from a 3D model. Note that I am not proficient with all of these programs, but have attempted to compare their capabilities by observing their operation by competent professionals.

BIM software solutions generally divide on two categories: unidirectional vs. bidirectional editing and single-file vs. multifile databases. All of these solutions initially design a 3D model and then extract views, such as elevations and sections, and other information. In a unidirectional approach, manipulating the extracted views and information will generally not automatically change the model or other views. Unidirectional approaches generally keep information in separate document files that are electronically linked, but where changes will not affect the model.

On the other hand, changes to extracted views and information in a bidirectional software, such as Revit, Bentley Architecture, ArchiCAD and VectorWorks ARCHITECT, do affect the model as well as all the other views and information throughout the project. To achieve this result, all information must be interrelated at all times. To create such a permanent interrelationship, the software solution must keep all the information about the project (models, views, sheets, schedules and so forth) in a single database file, or manage relationships between databases in multiple files. Though the bidirectional, single-database concept creates a very efficient operating environment, it also produces a much larger single file than those programs that use the unidirectional, electronically linked file solution. The single file, in the case of Revit and to a lesser extent with ArchiCAD and VectorWorks ARCHITECT, is probably larger than any DGN file or individual DWG file in an Architectural Desktop project, but is likely to be smaller than the total collection of files that make up an Architectural Desktop or MicroStation project. The multi-file approach is inherently more scalable and likely to perform better because it doesn't need to handle the entire model all the time, but it can require a bit more management and care in setting it up. Users need to weigh the pros and cons of each approach to match their needs.

Graphisoft ArchiCAD

Graphisoft ArchiCAD, introduced in 1984, was the first product among these solutions to create a virtual model. Now in its ninth version, ArchiCAD's bidirectional associative models keep all the data in one PLN file that can hold a 60,000-square-foot building—including all construction documents—in a 30MB file. ArchiCAD uses the GDL (geometric description language) model creation language. GDL contains all the information necessary to completely describe building elements as 2D CAD symbols, 3D models and text specifications for use in drawings, presentations and quantity calculations. The program also ships with the RCC (Richard Creveling database) that can be interpreted by Timberline software to instantly create Level 2 cost estimates.

ArchiCAD is a rare program—VectorWorks ARCHITECT is another—that is offered on the Macintosh as well as Windows platform. This is an excellent BIM program, and because it's been around the longest, it may have the most routines dedicated to architecture and construction. It's very popular in Europe and is used by prolific firms such as Davis Brody Bond in New York and D'Aleo and Associates in Baltimore.

Besides ArchiCAD, Graphisoft offers ArchiFM for facilities management and recently introduced a complete new product line for design/build firms, construction firms, engineering firms and consultants. This product set, which includes GS Constructor 2005 and GS Estimator 2005, allows companies to perform model-based calculations for scheduling, estimating and purchasing and provides a comprehensive platform with which they can manage an entire construction project. Constructor also includes a next-generation MEP modeling environment as well as a structural modeling library.

Autodesk Architectural Desktop 2005

Autodesk Architectural Desktop is an object-based BIM solution based on AutoCAD. Any improvements or updates to AutoCAD are reflected in Architectural Desktop. This solution uses specialized programming and routines to make AutoCAD perform as a BIM modeler (figure 1). It's a unidirectional solution that saves all information in separate DWG drawing files. Each file often contains information on disparate information such as doors and walls.
 Figure 1. Autodesk Architectural Desktop 2005 uses specialized programming and routines to make AutoCAD perform as a building modeler.
Figure 1. Autodesk Architectural Desktop 2005 uses specialized programming and routines to make AutoCAD perform as a building modeler.

These files are then linked by a programmed xref system called the Project Navigator so the program can interact with them. Architectural Desktop is unidirectional in that any change in the model is expressed in all views, but not all views can change the model. In most cases, Architectural Desktop's documents must be saved and views refreshed to update and coordinate all of its documents.

This five-year-old solution in its fifth version. It's the most widely distributed BIM software, due in great part to the large installed AutoCAD user base. Architectural Desktop is very capable and relies heavily on the automation of entity creation. It's very sophisticated software, so new users may have some initial difficulty, but in the hands of an experienced operator, it's very productive and capable of handling the biggest projects. Because it's basically enhanced AutoCAD, using the native DWG format, it's especially capable during the construction document phase. Because Architectural Desktop is very popular, several third-party books are available, and it's taught in many universities and community colleges. More third-party plug-ins are available for Architectural Desktop than for any of the other BIM solutions.

Bentley Architecture

Bentley Architecture is the architectural application within Bentley's multidisciplinary suite of solutions. It's an object-oriented product, and like its companions for structural and building systems engineering, it's based on the MicroStation platform. Because MicroStation has the second largest number of installed seats, there is a large pool of operators from which to draw. MicroStation or AutoCAD operators can easily become proficient with Bentley Architecture, and Bentley offers full DWG support to integrate with AutoCAD and Architectural Desktop users on mixed-platform projects.
 Figure 2. Bentley Architecture includes top-quality rendering and animation tools. Image courtesy of the Building Design Partnership.
Figure 2. Bentley Architecture includes top-quality rendering and animation tools. Image courtesy of the Building Design Partnership.

Bentley Architecture has been used by leading firms on many large and inspiring architectural projects around the world. For example, Bentley's architectural and engineering solutions are currently being used to construct a full multidisciplinary model of the Pentagon, the largest office building in the world.

Bentley Architecture includes full top-quality rendering and animation from within its user interface (figure 2) and also provides capabilities for modeling, visualization, reporting, schedules, cost and program analysis, bidirectional integration with engineering analysis applications, schedule simulation and 4D design. It also offers a capability called 2D/3D choice, which allows users to work in either the 3D model or 2D drawing views—or in both at the same time—while keeping all drawings and the models in sync.

Bentley offers a complete BIM solution for architects and engineers working on a single platform and supports those on other platforms through standard formats such as DWG, PDF, CIS/2 and the IAI's IFCs, making it very appealing for multidisciplinary teams and complex projects.

Autodesk Revit

Autodesk positions Revit as software purposefully engineered for BIM. Revit was conceived by programmers who created 3D software for the mechanical design industry and applied those concepts to create a solution tailored for architecture and construction. Autodesk vice-president Phil Bernstein has often called Revit the future direction of AEC software.
Figure 3. Specifically designed for building information modeling, Autodesk Revit provides bidirectional change capability.
Figure 3. Specifically designed for building information modeling, Autodesk Revit provides bidirectional change capability.

Revit is four years old and in its seventh version. Autodesk updates it about every six months. Third-party plug-ins are available for energy analysis and specification writing using Revit's export-to-ODBC functionality. Autodesk has not disclosed the Revit API (application programming interface), but this policy will begin to change when it releases Revit Structure for structural engineering and Revit Systems for MEP engineering, both currently in beta.

Revit is truly bidirectional in that any change to any object or any document view, including views on sheets ready to plot, is expressed in all documents and views (figure 3). The program is very intuitive and has an easy initial learning curve.

Many large architectural firms are doing pilot projects with this software, and SOM is using it for its 1,776-foot-high Freedom Tower project at the 9/11 site. Autodesk is expending lots of resources developing and promoting this software to the AEC community. For architects new to BIM, this software may be an excellent choice. Revit has the smallest user base because it's the newest solution. It is, however, an excellent solution and, with the backing of Autodesk, could become an industry leader.

Nemetschek VectorWorks ARCHITECT

VectorWorks ARCHITECT is developed by Nemetschek North America, a wholly owned subsidiary of European developer Nemetschek AG. Like ArchiCAD, it's a cross-platform BIM program that runs on the Macintosh as well as Windows operating systems. The developer suggests that smaller, price-conscious firms may be drawn to this product, which is the least expensive of the five packages reviewed. Although this program creates an excellent 3D model, it incorporates years of 2D CAD expertise to provide drafting and detailing capabilities (figure 4). The program's building objects display appropriately in both 2D and 3D and can be tagged with nongraphical information such as material, manufacturer and price.
Figure 4. VectorWorks building modeling capabilities make it easy to coordinate model views.
Figure 4. VectorWorks building modeling capabilities make it easy to coordinate model views.

This information can be reviewed and revised at any time during the design process and can be used to create schedules, tables and reports that are linked to the drawing through a built-in worksheet capability. Unique to this program is NURBS modeling capability, which allows VectorWorks ARCHITECT to create complex surfaces and organic shapes. The program also creates photorealistic and nonphotorealistic renderings with the included RenderWorks module. Fully compatible DXF and DWG translation from AutoCAD 2.5 to 2005 is available thanks to Nemetschek North America's status as a founding member of the Open Design Alliance. This software is available in seven languages and sold in more than 80 countries. Studio Daniel Libeskind used its 2D capabilities for designing the winning entry in the World Trade Center competition.

Weigh the Options

Familiarity with a program is the biggest productivity advantage. Features are important, but if the operator is not proficient with the software, productivity is hampered and profits fall. Is the program a standard? Autodesk's AutoCAD and AutoCAD LT have the largest worldwide user base by far, and Autodesk's DWG file format is considered an industry-standard file exchange format.
In This Article
In This Article

All these programs are not equal in creating a building model. Some will extract information more easily than others. The quality of the interfaces and the ease with which a model is created are debatable, because familiarity and workflow preference play such important factors. All of these programs produce most types of construction documents required for any level of building, and all are being used, often in concert, on real projects.

ROI is hard to predict because of personnel capabilities, and that is again a function of familiarity. As far as features are concerned, all these developers are competitive and will strive to offer the same capabilities if demand is there. Because of bidirectional capability and programming specifically for the architectural and construction industry, Revit and ArchiCAD can instantly create cost estimates directly from the 3D model using preprogrammed defaults, but may be limited in how much they can be customized. On the other hand, Bentley Architecture's powerful datagroups capabilities and links with Excel make cost and other types of reporting extremely powerful and customizable, but require more initial setup by the user. Graphisoft has the longest history with BIM software, and VectorWorks ARCHITECT's strong selling point is its affordability.

All of these software solutions create 3D models, extract automatic sections and elevations, and create, draft and document to standard 2D construction documents. Statistically, though Bentley Architecture and Architectural Desktop each have a large number of installed seats, it's not possible to determine if they are actually being used for building modeling or simply for standard 2D drafting. However these two solutions do offer a way for users to combine familiar 2D drafting with building modeling as they learn the new capabilities."

What Program is Right for Your Company?

Answering this question depends on how you rank your needs. Each of these solutions has clear areas in which it excels. The key to making the right selection is finding a match between a program's capabilities, your needs and the support and training the vendor can offer you. Factors to consider may include, but should not be limited to, your existing computer equipment, the importance of collaboration, available support, ease of use and room to grow and handle needs down the road.

Next, contact vendors and ask them to demonstrate how their software meets your needs. If possible, instead of a canned presentation, have them demonstrate on one of your projects or do a pilot project with them. Be sure that your staff is involved in the selection process. They should be willing to learn the new software and accept the work environment it provides. Also, check to see if there is good training available, either from the vendor or a third-party consultant.

Most importantly, recognize that choosing to implement BIM is a strategic decision. BIM software is the direction for the future and can add to your bottom line through increased profits and ROI, but only if you choose a solution that meshes with your needs.

Have an open mind, ask the hard questions and dig deep—a slick demo shouldn't determine the winner. No matter what you choose, it will be a big change, so don't choose the book by its cover.

H. Edward Goldberg, AIA, is a practicing licensed architect, industrial designer and AEC industry analyst. Ed's full-length book, Autodesk Architectural Desktop 2005: A Comprehensive Tutorial (Prentice Hall, 2003) is available now ( His other books, Autodesk Architectural Desktop 2004: A Comprehensive Tutorial and Autodesk Architectural Desktop 3, are also available. You can reach Ed at His personal Web site is

More News and Resources from Cadalyst Partners

For Mold Designers! Cadalyst has an area of our site focused on technologies and resources specific to the mold design professional. Sponsored by Siemens NX.  Visit the Equipped Mold Designer here!

For Architects! Cadalyst has an area of our site focused on technologies and resources specific to the building design professional. Sponsored by HP.  Visit the Equipped Architect here!