Building information modeling (BIM) is a tool for designing buildings and other structures. As the name suggests, it’s a software-driven process whereby we create a highly detailed digital 3D model. This approach is different from and better than CAD because it’s 3D. We can place each component or design element precisely in three dimensions and avoid “collisions” or “clashing.”
The Problem of Clashing
Clashing happens when different components are set up to be in the same physical location. Usually we mean MEP components—mechanical, electrical, and plumbing. This problem has happened in the past when designers have had only 2D tools to locate components in space. They left the details up to the construction crew to sort out on site.
Using BIM to optimize the design at the digital stage, before anything has been built, enables easier design tweaks to eliminate clashing. It’s faster, easier, and cheaper to optimize digitally than physically.
Though clashing has typically been expected when working in 2D, it is vastly lessened with BIM. When we use BIM, we create a much more precise and detailed model that shows exactly where the conduit, ductwork, plumbing supply and drain lines, light fixtures, and so on are located in the space. It’s precise, and it’s 3D. The tradespeople don’t have to interpret the details of the plan, as they’re laid out explicitly.
The Old Way
Working with a 2D drawing, in contrast, all the trades will need to look at the drawings and interpret where the components go. The design information is not included in the plan in that much detail—certainly not in 3D. Sometimes the contractors work together well in this model and come up with efficient and coordinated solutions on site. That is the model for the last few decades, but it’s really not optimal anymore.
Without using BIM, what this means is that the contractors and subcontractors working from 2D drawings have to look at the actual built 3D space they’re standing in and figure out how they will get their HVAC ducting, or wiring, or water heaters into the space. Since they don’t always confer with the other trades, especially those coming in later, this sort of “first in, first out” approach leads to collisions among those different components.
Additional BIM Benefits
In addition to minimizing collisions, the BIM program generates a schedule and materials list and updates it in accordance with all design changes. So when the architect revises the design from 83 light fixtures to 77 fixtures, the schedule and materials list change, too. That information is “attached” to the design and cuts down on common errors that occur when someone overlooks or doesn’t receive a document or update. It’s a more efficient and comprehensive plan for everyone to work from, and it’s easier to ensure that everyone has the latest plan. Changes are still going to occur during construction, but everyone gets their hands on the updates in real-time.
Another Level of Information
The “information” function of BIM is also a crucial differentiator of BIM from CAD. When I am working on a design and need to place an air handler on the roof, for example, I select it and place it into the design. It comes along with various information attached, such as the electrical load, CFM (cubic feet per minute) and many other specs. It’s a much finer level of detail and design.
All of that information is included at every subsequent phase of the model, so the schedule, the materials list, and so on are always updated whenever anything else is updated. Whatever component I select in the model shows me more information and specs. That information is also available to the construction crew when they’re on site and building the project.
The Effect On Budget and Schedule
So what does this mean for two crucial metrics, budget and schedule?
For the schedule, we’re trying to get all design work done in the pre-construction phase. We want to minimize the number of field changes, and we want to minimize the number of decisions the field crew has to make. We design first and the crew builds to the design, or to the model. We expect that by using BIM and optimizing the design, we will spend more time in the design phase and get it fully sorted out digitally. Because we spend that time, we expect the crew to build to the model without needing to create solutions on site. That was, no surprise, commonplace before using BIM. It still is, actually, for many crews.
Since we’ve done the clash detection digitally, we want to have no clashing at the construction phase. This is key to staying on time and on budget. We expect that our engineering staff will cost a bit less on an hourly basis than union contractors, so when we frontload the work, we can keep the cost overruns to a minimum. We want to depend on our engineering staff to use the power of BIM to design everything with no clashing before construction starts, rather than to say “the crew will figure it out.”
Any field changes—and there will always be field changes—cost more than digital changes, in both time and money. What may take 10 minutes in BIM may take a day or more to sort out on site. In addition, any changes that have to be made in the field may require additional materials and/or equipment, which may not be available instantly. This sort of snag is a major drag on the schedule and the budget, and often manifests as sort of a “slow leak,” rather than a major work stoppage. It’s one snag after another over the course of a project. We can do better with BIM.
Greater efficiency is often about sweating the details, and using the best tool we can get. Right now, BIM is the best tool that gives us that greater efficiency. It’s a game changer.