What is BIM?

A building information model includes 3D geometry, like a CAD (computer-aided design) model, but also adds additional information. The additional information can be material, part numbers, construction details, cost and other nongraphical data. It can also be functional or process information.

A BIM model falls between a CAD model and a digital twin in terms of the type and amount of information it contains.

Whereas a CAD model can convey information from the design phase to the construction phase, the richer BIM models can convey information during the building management process to owners, facility managers and maintenance staff.

Popular BIM applications include Revit by Autodesk and Archicad by Graphisoft.

BIM is sold as offering these advantages over CAD models:

• Reduced project costs
• Less confusion
• Less waste and rework
• Use downstream of design (for ease in handover, lower operating and maintenance costs, etc.)

BIM advantages hinge on the principle that putting information that is available to the architect or engineer during the design phase into a building’s model can be extracted by others down the line—first by those building it, second during the handoff to the owner, and third by those managing and maintaining it. For example:

• The general contractors could extract the exact building materials and quantities with greater accuracy than if they were counting parts on the screen or in a drawing.
• Renovations of a building might call for structural knowledge of the building, which would be extractible if the structural steel were inserted in the model.
• Maintenance staff could find service schedules for the HVAC because the BIM model would have model names and numbers.

However, some of the advantages claimed by BIM are only possible if the BIM model coexists with other technologies. For example, the “less confusion” claim because everyone is on the latest version of the model is possible only with version control as supplied by a product data management or the model is shared from a central source, like the cloud. “Less rework,” such as the result of fewer clashes, is possible because BIM software uses solid modeling.

BIM models take longer to set up. Because BIM models contain more information, design firms must account for the time it takes to enter the information.

BIM software is also more expensive than CAD software.

The concept of BIM first appeared in a professional commercial CAD program with Archicad, so most CAD insiders consider Archicad the first BIM program. However, Graphisoft referred to its model as a “virtual building” or “single building model.” Bentley referred to its model as an “integrated project model.” In 2002, Autodesk published a white paper titled “Building Information Modeling” and from then on, threw its superior marketing prowess behind it, leading to the rapid adoption of Revit in the U.S. and the origin of BIM being associated with Autodesk.

However, the origin of BIM goes back to 1960 when visionaries coined the term—ahead of any computer that could make BIM useful to mainstream architects.

Rudimentary BIM software applications first appeared in the 1970s, like Chuck Eastman’s Building Description System, RUCAPS and Sonata. However, their rudimentary interfaces and the expense of computer hardware limited their adoption. Here’s a basic timeline:

• 1987—Graphisoft launches Archicad
• 1992—G. A. van Nederveen and F.P. Tolman were the first to specifically use the term “Building Information Model.”
• The mid-1990s saw the emergence of BIM software on PCs, and for the first time, architects had access to it.
• 2010s: National and international governments began mandating or encouraging BIM use in public projects.

Today, BIM is widely used across the AEC industry, especially by big firms in the U.S. and Europe.

The information contained in a BIM model can vary according to the AEC software vendors that create the BIM programs. There have been attempts to standardize the type of information included in a BIM model by various agencies and national governments.