With their vast capabilities, emerging building information modeling (BIM) technologies continue to challenge and transform the construction industry. BIM software can operate in the cloud, conduct virtual design collaboration, convert files into different programming languages, simulate the effectiveness of design, detect errors in design, and model building energy use. However, it isn’t a completely autonomous tool.
Quantity takeoff is a common feature in BIM software, and add-ons can enhance its quality. These augmentations are significant because taking-off quantities consumes a lot of time. Such tools relieve estimators from mundane tasks and allow them to focus on improving the quality of their cost estimates.
Like any software, the BIM quantity estimate’s accuracy depends on input information. In other words, the type of information available to the designers and engineers at the time of design, the project stages (conceptual to detail design), the designers’ and engineers’ experience, etc., affect the output estimate’s accuracy. Any shortfalls in the BIM designs can cause the BIM quantity estimates to be inaccurate. The BIM operator’s knowledge and background often drive the drawings’ quality and relevance.
Estimators must understand that most BIM drawings are not developed for estimating purposes. As a result, estimators must realign BIM quantity estimates accordingly.
Since designers and engineers do not look at projects the way estimators do, estimators must acknowledge the missing data in the BIM drawings, capture information that is not or cannot be presented in the drawings, and differentiate components that BIM assumes to be similar but are not (e.g., floor slab versus roof slab).
Essentially, an estimator has to restructure the BIM quantity estimates to accurately reflect the project reality.
There are many potential hurdles and pitfalls. For example, while the models for most structural and architectural components (such as concrete, steel, doors, windows and drywall) are readily available on BIM software, the models for mechanical, electrical, plumbing and other exclusive products/equipment (e.g., patented products) are not. To protect their exclusivity, companies that own the rights to products and equipment aren’t likely to share their designs with BIM software suppliers or designers, meaning these models are often left out of BIM drawings. As a result, the estimator must measure these quantities accordingly, which adds time to complete the estimate.
Knowledge of sustainable design and construction is crucial to the design and project staff because the methods used to complete a project can affect its bottom line as much as the materials. Such knowledge includes Leadership in Energy and Environmental Design (LEED) certification, energy audits and alternative-power sources. Sustainable design considerations that affect contractors include use of products and materials that contain highly renewable, recycled and reused materials; avoidance of products and materials from sources farther than 500 miles; use of energy-efficient equipment; recycling, reusing and minimizing the disposal of on-site wastes; and the reduction and elimination of on-site air and noise pollution. Other sustainable design components that do not directly affect contractors are increased use of green spaces and green roofs; a more congested site (due to location); the use of renewable energy; and the increased use of glass and open space design.
Unfamiliarity with sustainable design has created fear among contractors, but it usually quickly dissipates once they take on their first green project and understand their role in it. Similarly, an estimator has to understand their role in sustainable design. The most significant change is procurement practices (i.e., where to buy). Unfamiliar and untested sources may adversely affect the project schedule and productivity.
An estimator also must know the difference in cost and construction methods of green materials and energy-efficient equipment. An estimator must understand the recycling process and the effect of green materials and processes on construction productivity.
Working with unfamiliar materials, designs, processes and procedures (such as disposal methods, green roofs, wind turbines, pollution monitoring, etc.) can affect a contractor’s job site productivity. Estimators must account for that period of adjustment. It’s also important to note that, if an estimator continues to work with such a team and it becomes familiar with sustainable practices, the estimator must readjust the project estimate to exclude that unfamiliarity. Otherwise, estimates could continue to be high, and the estimator would not be capitalizing on the team’s experience, which is a base consideration for BIM estimates.
CHONG is an associate professor at the University of Kansas, Department of Civil, Environmental and Architectural Engineering. He researches and consults about sustainable engineering and construction engineering. Reach him at www.people.ku.edu/~oswald.