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BIM is no longer a novelty for construction companies. Initially embraced primarily by designers, BIM is now a common process used by contractors to work out the kinks in construction digitally before ever breaking ground on a project.

In fact, 32 percent of contractors expect to increase their use of BIM in 2016, according to a recent survey, The Challenges Facing a Growing Industry: The 2016 Construction Hiring and Business Outlook. Most contractors are familiar with the 3-D visualization advantages of BIM. Some contractors also may be using what is called 4-D BIM, which connects scheduling information to the model. But 5-D BIM, also called model-based cost estimating, is just moving out of its infancy despite growing interest in using it to better define project costs.

The advantages of 5-D BIM

Estimators within construction and AEC firms currently are using models primarily to do preliminary conceptual estimates or as a double-check to their 2-D takeoffs. The models give estimators a visually rich representation of a project to check quantities and validate costs. The model also helps estimators better understand the complexity of a project and identify areas of potential risk from a cost perspective.

Contractors also are looking for better ways to integrate BIM tools with estimating software to speed up the estimating process. The goal is to pull as much dimensional information as possible from objects in the model, thus eliminating a time-consuming aspect of takeoff. This gives a construction company’s estimators more time to spend on value engineering and constructability reviews.

Ultimately, 5-D BIM will lead to more reliable cost feedback during the project planning stage. This results in greater cost predictability and minimizes later changes in project scope due to cost overruns. Even more advanced is linking both cost and the master schedule back to the model for visualizations, such as showing owners the project's cash flow.

Current obstacles

Kevin Miller, construction management professor at Brigham Young University, specializes in estimating from building models. He sees the difference in the quality of estimating information coming from models as one the biggest challenges to achieving the benefits of 5-D BIM. “We’re going through a transitional period where some designers are advanced at using BIM and some are still learning it,” he explains, “so the amount of estimating-related information included in a model can vary greatly.” As a result, estimators have to refer to 2-D drawings to get details, such as floor coverings, that are often missing from the model.

Miller acknowledges that many 3-D modeling tools will generate 2-D information from the model, including floor plans, specifications and notes. However, the workflow to extract that 2-D information from the model for full-blown production estimates isn’t an easy process. “It’s much quicker for estimators to use the 2-D takeoff tools they’re used to,” he says. Consequently, estimators currently have to use multiple, unconnected 2-D and 3-D takeoff systems, complicating the process and increasing the chances for error.

Another concern with models is the lack of specifications that estimators need. From a design perspective—particularly for independent architects—there’s often little value to putting specs into the model. In fact, it may not be possible to build a model containing all the job specifications without impacting model size and performance.

Taking the next step

5-D BIM is entering a new level of sophistication, this time focused squarely on the needs of estimators within construction and AEC firms. While the information contained in a 3-D model will continue to advance, estimators will realistically continue to rely on 2-D information to supplement models for some time to come. New technology addresses this by making it possible to do production estimating work simultaneously using both 2-D and 3-D content.

Essentially, estimators no longer have to learn and use more than one takeoff tool to work with models, or rely on other cumbersome procedures. This streamlines the now fragmented takeoff process, eliminates additional error-prone work and allows estimators to better visualize their takeoff.

The ability to link construction objects in a model to assemblies in a customized estimating database is now possible, providing the estimator with the specification variables that are often missing in models.

Construction estimators view models differently than the designers who create them. Today’s technology is recognizing this difference and making it easier for the two disciplines to share information. Clash detection, safety issue identification and trade coordination are all popular ways contractors use BIM. Now, greater constructability from a cost perspective can be added to that list.
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