Where BIM Falls Short for Quantity Takeoffs

October 17, 2018

There’s a lot of buzz about both the disruption and efficiency of Building Information Modeling (BIM) systems. As the construction industry relies more and more on BIM for building projects, there is pressure mounting for the cost estimator to use BIM for takeoffs.

But is BIM really the death knell for quantity takeoff? Can BIM ever capture all the same nuances as a two-dimensional drawing? For contractors, BIM is a great way to share information and collaborate when it comes to planning, designing, constructing, and managing projects. With BIM, the contractor and owner can be more efficient when it comes to working through project conflicts before anyone sets foot on a construction site.

Understanding How BIM Works

For preconstruction estimating departments, BIM is an emerging technology that can be used to create a digital representation of a building. With BIM, contractors can use a model to clearly see dimensions and product information for walls, doors, and windows. For example, cost estimators can incorporate any rules they may have about how to position a door and a light switch so the door and light switch is always positioned correctly in relation to one another throughout the model.

Here’s how it works: the BIM system creates a takeoff automatically by the act of designing the building with “intelligent objects” instead of static lines. BIM technologies include libraries of three-dimensional objects (with associated data) that can be brought into drawings.

However, while the objects contain common attributes, they lack data about site-specific requirements, such as a concrete foundation that requires a certain amount of rebar, a specific type of concrete, the amount of excavation and formwork. This site-specific data is not included by the project designer, but must be addressed by the concrete estimator.

BIM vs. Quantity Takeoff

No one wants to turn the clock back to the time of calculators, floppy disks, and faxes for cost estimating. But it is nearly impossible for a single designer to include the uniqueness of each trade. Designers do not typically deal with methods and materials. For example, they may know that a wall needs to be framed, but they don’t tell you how the wall is to be framed.

In a BIM model, estimators can look at an object in a three-dimensional fashion and see its height, width, length, and other attributes. Objects have descriptive data “attached” so when the object is brought into the drawing, the attached data is automatically brought into the project. The estimator then enters the number of hours it will take to install and enters the unit cost.

While the trade estimator can use BIM, many times they would want to use the two-dimensional drawing to better understand the nuances of what the BIM model is trying to represent.

Is BIM Killing Takeoff?

Clearly, BIM is gaining a foothold with nearly a third of those participating in the 2017 ConTech Survey saying they have a BIM department. While BIM can help construction firms detect problems, visualize, and project plan, there is a learning curve when it comes to constructing the model correctly. As cost estimators get trained to work on BIM, more issues can be solved digitally before projects ever start to avoid physical re-work later.

As you can see, the rumors of BIM killing takeoff may have been exaggerated. The tools of the trade may change, but the job of ensuring accurate quantity takeoffs will remain the same. While BIM may allow anyone using on-screen takeoff programs to generate quantities, it will still require professional estimator skills to analyze and interpret the data and review and determine material and labor costs.

Want to explore this issue more? Go ahead and download On Center’s white paper,Is Takeoff Dead?” It provides a closer look at how BIM falls short when it comes to adding data elements or additional drawings to a project.

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