Quantity Take-Off in Model-Based Systems

In recent years, as Information Technology (IT) tools and Building Information Models (BIM) are adopted by more practitioners, it has become apparent that it is possible to have a faster and more efficient quantity take-off system. The efficiency of quantity take-off lies in the smart transfer of the information produced in the design process to construction. Existing BIM-based quantity take-off is performed in the design phase of a project. BIM-based systems provide a smart platform for information exchange between design and construction. A “model-based” system refers in this paper to a Building Construction Information Model (BCIM) coupled with a location-based scheduling process. BCIM offers an environment in the construction phase, where data are stored, updated, and reused via the evolving project libraries of a building contractor. BCIM is composed of three sub-models: (i) a building product model that provides the sections and quantities, (ii) a building resource and cost model that provides activity lists and labour consumptions to calculate activity durations, and (iii) a building process model that introduces the interdependencies of the activities. In the location-based scheduling process, a preliminary master schedule is obtained automatically from an information database, and then improved by the planner to fit the conditions of the company and of the project. The use of Advanced Line of Balance (ALoB) is proposed in location-based scheduling. The objective of this paper is to introduce the principles involved in quantity take-off in a “model-based” system as implemented by a contractor. The paper consists of three parts: (1) the “model-based” system (composed of BCIM and ALoB) is introduced as the theoretical background; (2) the steps in performing quantity take-off in “model-based” systems are described; and (3) Two residential construction projects are used to test the proposed quantity take-off principles.