BIM Modeling Guideline to Enhance the Accuracy of Architectural Walls Quantity Takeoff: Case Study of One Story Residence
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The quantity takeoff method using the BIM tool is proven to be faster and reliable than the traditional 2D-based method. However, this is not an automatic process. Some data can be underestimated due to incomplete modeling, while some data can be overestimated due to overlap modeling. The research objective is to propose BIM modeling guideline for enhancing the accuracy of architectural walls quantity Takeoff with the case study of one story residence. REVIT 2019 was used in this study. BIM based quantity takeoff results with difference modeling method were compared with manual quantity takeoff. The results showed that the ways to model the components (walls, structural columns, structural beams and floors) affected the accuracy of BIM-based quantity takeoff. Inappropriate component modeling, such as no considering of object overlapping, and double count in a material takeoff report can make the error about -23.46 to 30.65% in quantity takeoff, or -5.08 to 24.01%, or -4,188 to 19,787 Baht in cost estimation, comparing with actual construction. While, the accuracy of BIM-based quantity takeoff came with appropriate component modeling, such as consistence wall height modeling with real construction, using the join geometry command, and careful considering in a material takeoff report. Finally, the results showed that BIM-based quantity takeoff with this BIM modeling guideline give the accuracy architectural wall quantity takeoff with only -2.12 to 4.70% error in quantity and 0.76% or 966 Baht errors in cost estimation, comparing with 126,898 Baht of second manual quantity takeoff. While, first manual quantity takeoff had a mistake from incomplete count.