For various participants ofprojects, accuracy in the estimation ofproject duration is vital at various stages of the building production process. The importance of the problem has been acknowledged by the indust y worldwide, and various models have been proposed in the literature, but all have their limitations. This paper presents a performance-based durationestimation model that utilizes historical knowledge, in particular information to estimate the worst, best and likely variances of current projects by using the unijied structure of an information system developed for designlbuild organizations. The model allows the estimators to make use of data on past projects. Proposed organizational pattern, designlbuild, are vital for accessing the as-built schedules and variance infomation provided by construction groups in a designlbuild organizational pattern. Ourfinal solution includes an integrated relational data base model developed for designlbuild organizations that provides the integration of satellite sofiwa re packages, thus eliminating additional efforts for obtaining the data needed in the estimation process