Faster and More Accurate Quantity Calculations with BIM

BIM can cut the work expenditure for the quantity survey in half. Also, as a basis for estimates, calculations and cost accounting, it is more accurate than manual methods. Those are the results of an open-BIM project of Graphisoft, the manufacturer of Archicad, with eight manufacturers of software for quantity surveying, tender, award and invoicing of building costs (AVA). The reason: An AVA software module calculates surface areas in m² and volumes in m³ from the geometries 
of the building components. It immediately performs what can take days when manual methods are used for complex projects.
   
In the project under discussion, the quantities of a test building were calculated in different ways: the BIM model was exported from Archicad via IFC to the various programs for quantity surveying. The result: the calculated quantities are practically iden-tical. The deviations from the reference method – manual quantity surveying – were between 0.05 % and 0.85 %. As experienced calculation personnel from offices consisting of one to 120 persons 
confirm, BIM quantity surveying in everyday use is much more precise than the manual method. Because with that method there is a tendency to make allowances for safety margins, which add up to substantially higher deviations than with BIM. However, the BIM quantity survey requires that architects consistently use 3D modelling and comply with certain modelling guidelines. This method facilitates work in all project phases, since any adaptations and modifications in the planning are transparent.

The special publication DETAIL selection "Digital Processes, BIM" is available here.