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BIM model-based quantity takeoff: Betterment of cost estimation

As the construction industry starts to shift the focus towards undertaking to accomplish more complex projects, BIM becomes more important. What started off as a plain geometrical modeling in 3D has today transformed into complete time scheduling 4D modeling and cost planning 5D BIM modeling for construction firms.

5D BIM modeling and cost estimation

The feature of 5D; model-based estimation and quantity estimation function of BIM holds the roots to significant automation and innovation in the building construction industry. 5D BIM modeling connects a 3D object, its parts and the entire assembly model to the external third party cost estimating software. Whenever a change in the design geometry or quantity is changed, the changes are automatically reflected in the cots.

This alliance between BIM platforms and cost calculation software allows the quantity surveyor, estimators, and planners to evaluate the impacts of design changes on costs and stay on the budgets. It also reduces the iterations for estimation, approximation needs, and bidding becomes accurate.

5D BIM – an onscreen quantity takeoff; offers an interface that supports better decision making to engineers and contractors. It dives predictability in the building construction project, brings certainty in planning the logistics and scheduling. Planning with 5D BIM cost estimation saves estimators from going haywire and plan their relationship with sub-contractors in settling the costs and communicate with BOMs.

Model-based cost estimation to stay on budgets

The economic slowdown on a global level also plays a major role in the sudden adoption of BIM and its evolution – especially the growth of 5D BIM modeling service providers across the globe. A large sum of money is being invested in the construction industry with each passing day and every stakeholder and construction firm needs efficiency and predictability.

Simultaneously, the subcontractors also need some backing with the documentation to coordinate the tasks with inter-teams and cost negotiations with an external organization when projects involved prefabrication. But with 5D BIM cost planning and material takeoffs, the estimates, bids, and the schedules can be made accurately.

One may find several studies that show the positive impact of BIM on several complex building construction projects with BIM model-based estimates. Almost half the contractors report positively when it is about cost estimating with BIM platforms like Revit.

They see great potential with the platforms like Revit as it eliminates the need to develop a thorough understanding of drawings and then calculate QTOs from Blueprints by manual methods. This reflects greater accuracy in the outcome and uncertainty almost nil.

Currently, with technologies like VR, and high-end cost estimation software, the on-screen estimation has been breaking down the barriers and resistance to adoption of BIM amongst the surveyors.

5D BIM modeling and interoperability for general contractors

General contractors are typically amongst the most beneficial people with BIM-based cost estimation and QTOs especially for costly items like façades, MEP equipment, etc. Earlier, there were 2D drawings for all these and it consumed time, caused blocks in the process and yet the final numbers were approximate. With 3D BIM modeling and addition of 4D and 5D elements to it, the entire process of cost can be done in a unified environment often termed as VDC.

Design data exchanges with COBie formats have enabled professionals from across the discipline to share and exchange the information without design data loss. Building product manufacturers, steel fabricators, engineers and architects working under the same contracting team can essentially exchange their design 3D models and the estimator can finally prepare a coordinated BIM model to deliver the estimates and order quantity. This interoperability has made the general contractors to trust their decisions more and become an expert in resource management.

Benefits of 5D BIM modeling and on-screen cost estimates

Apart from the increase in efficiency of estimation and closeness to the actual expenditure, there is also a significant amount of time-saving when estimates are done with BIM. Several contractors claim that when the takeoffs are calculated with BIM, the tasks are done 3 to 5 times faster than the manual methods and the overall project time by half.

All these together enable the estimator for value addition during the early phases of design and construction planning wherein the cost calculations are more accurate. Also, when the BIM platforms are linked with the cost estimation software it gives the design engineer to alter the design without the worrying about the tedious process of calculation from scratch.

Another important takeaway with BIM-based 5D BIM modeling is that the change management can be expedited. Now for complex building construction projects like the commercial construction of a shopping mall or a healthcare facility, the worst situation that can occur is finding out there is a design change and that the estimate will change. But with BIM and integrated project delivery these changes can be handled easily without hassle.

Final thoughts

Also, direct shop drawings and fabrication drawings for steel and other building products can be extracted directly from BIM as-built models. The BOMs prepared within contributes largely in deciding the over the cost of the project, coordination and between fabricators and contractors.

Thus, with the correct techniques, it is very much possible to deploy make the complete use of 5D BIM modeling, accelerate the design and construction planning, gain control over the expenditure and gain quality.

Note: This is a guest blog by Usha B. Trivedi, engineer with Hi-Tech CADD Services.