The Accuracy Enhancement of Architectural Walls Quantity Takeoff for Schematic BIM Models

The emergence of Building Information Modeling (BIM) technology makes the quantity takeoff process faster and more reliable. It helps reduce the effort in cost estimation to survey the cost feedback on alternative schemes in the early stages of design. However, at these stages, the quantity could be absent or in excess because the BIM model has a low level of development (LOD). The building elements that have layered structures such as architectural walls always face such problems. This is because during the construction phase, each layer may have a different dimension. For instance, the height of the interior finish layer of the wall may be shorter than that of the core layer. On the other hand, the walls in a BIM model during the early stages usually have low LOD. Each wall layer is not created separately and some walls may overlap structural elements because the designers need a schematic BIM model that is easy to create and manipulate. This research proposes a method that will improve the accuracy of the wall quantity takeoff in the schematic BIM model by applying the concept of BIM-based clash detection. The proposed method automatically detects the overlapped areas and subtracts or adds the material quantity of each wall layer without the need for editing the BIM model. The now accurate quantities can then be used in the chosen project delivery method where a cost estimation feedback is needed during the early stages of the design process.