An integrated knowledge-based system for alternative design and materials selection and cost estimating

Abstract

Building design and material type used are the two main parameters that have a significant impact on the cost of a building. Therefore, it is important for a cost estimating tool to have a mechanism that allows the designer to perform a rapid `what if' analysis on design alternatives and materials selection at the early planning stage without the accompaniment of detailed design and drawings. However, the traditional design cost estimating procedures generally focus on assessing costs after design decisions are made and conveyed to the construction drawing as a quantity take off. On the other hand, comparative cost estimating (unit cost per square meter) uses historical data collected by averaging buildings of different designs, heights and materials. Even today's computer aided design (CAD) software incorporates a mechanism to take off quantities from completed designs and drawings. However, basically they are the same as the traditional quantity take off estimating because a single specified design still controls the resulting costs, and there is no alternative materials selection integrated to the cost system. This article presents an integrated knowledge-based system for alternative design decisions, materials selection and cost estimating mainly for pre-design analysis. The knowledge-based system also includes materials selection and cost estimating for after-detailed design by providing edit tables for inputting the dimensions of building elements from completed designs and drawings or by directly importing from CAD. The system generates activities quantities, costs and lists of materials selected and their respective quantities. An analysis of alternative design and materials selection for a residential building using the integrated system is presented.