This paper deals with the analysis of the Expected Shortfall of the makespan in activity networks when uncertain activity durations are modeled by intervals. More precisely, for each activity only the interval for its integer valued duration is known to the decision maker. In this scenario, we address the evaluation of the Expected Shortfall associated to a feasible schedule discussing its role and importance in decision support systems for planning and scheduling applications. We propose heuristics to determine a fast estimation of the Expected Shortfall. The computational results show that it can be used as optimization criterion for a wide class of planning and scheduling problems while modeling the risk-averse behavior of a decision mak...