Cost Estimating in the Age of 3-D CAD Software and Object Databases

Abstract

Cost estimating is a vital activity for contractors. An estimate is not only necessary for proposal preparation but also for several project management functions. Despite the importance of estimating, it has remained a very time consuming process. The most inefficient part of construction cost estimating is determination of the amount of resources needed for the construction of a project -- also known as quantity takeoff. The quantity takeoff process is still very slow, is not very accurate, and does not eliminate the possibility of an estimator missing or duplicating estimating items. New parametric CAD software is revolutionizing the way architects design buildings and will significantly increase construction cost estimator productivity by substantially reducing the manual work necessary for performing quantity takeoff. The data model of parametric CAD software allows easy exchange of building design information among various software systems used during design, construction and service life of projects. This paper discusses the architecture of an object-oriented estimating system that eliminates the need for manual quantity takeoff by obtaining the necessary building element dimensions and properties from the project CAD model. The paper explains how Autodesk Revit parametric CAD software exposes project information and the class diagram of an object-oriented estimating system that performs quantity takeoff by obtaining project information from building models prepared using Revit. The paper uses an object-oriented database for persistence of estimating objects and discusses the advantages of object databases over relational databases for applications with a complex information model.