Modeling construction time in Spanish building projects

• We propose a forecast model to estimate the construction time of new builds.
• Gross floor area (GFA) has greater influence than cost on the construction speed.
• Both GFA and cost are necessary factors to obtain the most accurate forecast model.
• We develop a stability analysis to validate the proposed forecast model.
• We analyze the model sensitivity versus the variability of construction costs.

The literature states that project duration is affected by various scope factors. Using 168 building projects carried out in Spain, this paper uses the multiple regression analysis to develop a forecast model that allows estimating project duration of new builds. The proposed model uses project type, gross floor area (GFA), the cost/GFA relationship and number of floors as predictor variables. The research identified the logarithmic form of construction speed as the most appropriate response variable. GFA has greater influence than cost on project duration but both factors are necessary to achieve a forecast model with the highest accuracy. We developed an analysis to verify the stability of forecasted values and showed how a model with high values of fit and accuracy may display an anomalous behavior in the forecasted values. The sensitivity of the proposed forecast model was also analyzed versus the variability of construction costs.