Systems design may be used profitably in all phases of building design. Systems design, however, is most advantageous in the early design stages. One system may be substituted for another, and components may be eliminated or combined in those stages with little or no cost.
Systems design should be preferably applied in the contract documents stage only to the details being worked out then. Major changes are likely to be costly. Value analysis, though, should be applied to the specifications and construction contract, because such studies may achieve significant cost savings.
Systems design should be applied in the construction stage only when design is required because of changes necessary in plans and specifications at that time. Time available at that stage, however, may not be sufficient for thorough studies. Nevertheless, value analysis should be applied to the extent feasible.
