Before delving into the main content, I would like to clarify that my references to CAD and BIM are not tied to any specific software or technology. Instead, I use these abbreviations to symbolize two distinct eras. As is widely known, CAD stands for Computer Aided Design. Here, it represents the period when drafting boards disappeared and hand-drawn drawings became obsolete—a change that occurred nearly two decades ago.
BIM, which stands for Building Information Modeling, represents the era we are now entering. This era is still taking shape, so its exact characteristics are hard to define. If I had to summarize it, perhaps it could be described as “the owner knows best.” Prior to CAD, we had the manual era, characterized by flat drawing boards and T-shaped rulers.
The reason for this distinction is simple: no matter how times change, our fundamental goal remains unchanged—to build better homes more economically and enable humanity to live more poetically.
During the CAD era, many tasks from the manual era persisted, such as calculating engineering quantities and using design manuals. Similarly, as we move into the BIM era, some CAD-era tasks remain, like structural calculations, as well as tools such as rendering and virtual reality software.
So, what differentiates the CAD era from the BIM era?
1. Tool Level: CAD is like Word, BIM is like Excel
If we compare the main tools of each era, this analogy helps clarify the difference. For professionals, the comparison between Word and Excel mirrors the distinction between CAD and BIM. A financial report looks similar in Word and Excel, but behaves differently. If you change a number in Word, you must manually update related figures. In Excel, changes propagate automatically through formulas.
In other words, a report in Word is merely a snapshot of an Excel sheet—just as a person’s portrait is only one view, while a real person can be seen from multiple perspectives and even through scans like CT, ultrasound, or X-rays.
The CAD and BIM comparison is similar. Buildings are typically depicted through floor plans, elevations, and sections. In the CAD era, designers created each view separately. In the BIM era, all views derive from a single model. Changing a door or wall’s type means manually updating every drawing in CAD, but only updating the component in BIM.
Furthermore, design and construction require structural, thermal, energy-saving calculations, and quantity statistics. In the CAD era, each adjustment meant modifying multiple models to reflect impacts. In the BIM era, the building model is used directly for calculations, and adjustments require updating only the unique model, enabling high automation.
As a side note, comparing CAD and BIM to Word and Excel is not novel—many have made this analogy before me.
2. Method Level: CAD is “I make clothes for you,” BIM is “I tailor clothes based on your body”
Project construction involves many disciplines—sometimes twenty or more—especially with the introduction of technologies like electricity, air conditioning, communication, and intelligent systems. This complexity has grown exponentially.
Simply put, even if a legendary craftsman like Mr. Lu Ban were alive today, he could only handle architecture and structure. Modern projects require specialists in plumbing, HVAC, electrical, energy-saving, communication, rendering, and more.
We have all these specialists, but how do they collaborate effectively to build a house?
Let’s examine collaboration in the CAD era:
First, the architectural specialist creates plan, elevation, and section drawings, then passes them to others. The rendering specialist uses these to build a model for visualizations like renderings and virtual reality. The structural specialist builds a structural calculation model, performs calculations, and prepares diagrams. Mechanical and electrical specialists create their own calculation models, conduct analyses, and produce their drawings. The cost specialist establishes a quantity calculation model to estimate materials and costs. The green building specialist analyzes environmental benefits and emissions. After construction, the property manager builds a property management model for maintenance.
This process is simplified; it doesn’t account for conflicts, such as when mechanical and electrical specialists find their planned pipe routes blocked by others. Such conflicts are common.
To summarize:
- Each specialist works hard, but must first create their own “XXX model.” Are these models identical to the actual house? Even experts may alter them. When design changes occur, can all specialists keep up?
- Creating these models takes time, and for homeowners, time means money.
- Can these models be used for future maintenance, renovation, or expansion?
If building a house is like tailoring clothes, in the CAD era, each specialist creates garments based on their understanding, but the result may not fit the owner perfectly.
Now, let’s look at the BIM era:
Suppose the owner enlists a BIM specialist alongside the architectural, structural, and electromechanical experts to build, manage, and update a model that accurately reflects the real building and is usable by all. This is called the BIM model.
When the architectural specialist needs plans, elevations, or sections, the owner instructs the BIM specialist to extract materials from the BIM model. For structural calculations, the BIM specialist retrieves and updates information as needed. The same applies to mechanical, electrical, green building, and cost specialists.
BIM consolidates all information into a single model, enabling early detection and resolution of conflicts between disciplines.
During bidding, BIM can help owners provide accurate drawings and the completed BIM model to bidders, who then use the model to present their proposals.
During construction, actual progress can be tracked in the BIM model and compared with the planned schedule. Problems detected during construction are addressed within the BIM model, with updates reflected in real time.
After completion, the continually updated BIM model matches the actual building and can be used for marketing, sales, operation, renovation, and expansion.
Returning to the tailoring metaphor: BIM is about custom-fitting clothes to the owner’s body.
Final question: Does BIM specialist equal BIM consultant?
3. Result Level: CAD speeds up designer work, BIM empowers homeowners
Q: Who benefited most from the shift from manual drawing to CAD?
A: Designers.
Q: What was their greatest benefit?
A: Drawing became much faster.
Q: Who gains most from the move from CAD to BIM?
A: Owners.
Q: What is the biggest advantage for homeowners?
A: Cost savings—fewer changes, less rework, reduced extra investment.
Q: Any other benefits?
A: Time savings—issues are resolved immediately.
Q: Anything else?
A: Improved quality—no need to rebuild or drill blindly.
Q: Anything more?
A: No more.
Q: Is that really all?
A: Owners become more refined and knowledgeable, understanding their house better than anyone else.
Of course, achieving this requires BIM to be available whenever homeowners need it.
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