Comparison of Utility System Quantity Take-off for Residential Building using Building Information Modeling

Abstract

In order to calculate the amounts of materials for electrical and sanitary systems by using 2D construction drawings, it is complex due to the drawings only show the top view of pipe layout. In actual execution, installed pipes can be horizontal, inclined and vertical. These ambiguous layouts may result in mistakes and errors for quantity take-off. This study proposes the procedure to estimate the material quantity of utility system in residential building using building information modeling (BIM) which actual pipe layouts at the construction site were observed and interviewed from the site engineer, then the quantity takeoff results between BIM and traditional estimation from contractor’s bill of quantities (BOQ) are compared. The selected case studies are 2 types of two-storey houses on 240 and 280 sq.m. The study result indicates material quantities calculated from BIM are less than the traditional method. Three causes of deviation consist of 1) the actual pipe layouts were changed when installing at the real environment 2) the contractor’s estimation method is not clearly specified and 3) there are some redundant or substitute quantities which are added in traditional method. Thus, BIM can obviously assist the process of utility pipe layouts determination and accurately enhance the quantity take-off process