Calculating Float
Activities on the same network path share total float. Figure 35 shows a portion of the house construction project’s critical path through foundation and underground work. The critical path (in red) spans activities from “lay out and stake property and excavation” through the “pour footings and pads” activity. Two activities have total float available: “excavate for and install underground sewer” and “inspect underground sewer.”
Figure 35: Total Float and Free Float
While both “excavate for and install underground sewer” and “inspect underground sewer” have 4 days of total float available, only the inspection activity has 4 days of free float available. Any delay in excavating or installing the underground sewer will equally delay the inspection. However, inspecting the underground sewer may be delayed up to 4 days without affecting any successor activity.
Note that leveling overallocated resources on the “inspect underground sewer” activity is much easier than on “excavate and install underground sewer” because of the former activity’s available free float. Delaying the inspection by 2 days affects the resources assigned to that activity, but it has no effect on any subsequent activity in the network. But delaying excavation and installation affects also inspection and resource assignments for both activities. As shown in the figure, however, leveling resources will always consume float along a path of activities.