In most scheduling scenarios you want activities to schedule As Soon As Possible (ASAP). There are situations though when an As Late As Possible (ALAP) scheduling constraint better suits the schedule narrative.
The ALAP constraint schedules an effort to delay until total float is expended. In this way the work delays without affecting project completion. There a situations when an ALAP constraint helps to better drive the true schedule narrative. In Just-in-Time manufacturing for example you would want to delay the arrival of material until just before manufacturing. An ALAP possible constraint helps to model this manufacturing situation in the schedule.
In another example you would want to delay packing computer equipment until just before the scheduled move date. Other times you would want to delay training until the associated work nears in the horizon. In one final example you would want to delay worksite cleanup until just before the final inspection. ALAP constraints are possible in Primavera P6 Enterprise Project Portfolio Management (EPPM) software.
This article demonstrates the insertion of an ALAP constraint in a Primavera P6 EPPM release 16.1, schedule, Classic view.
Our demonstration project schedule is displayed in Figure 1.
This is a short piping repair project. Currently, the clean worksite effort is scheduled to take place immediately following insulate piping work. This makes sense in most situations, and it is nice to have the 1-day total float on clean worksite. But we really want to make certain the worksite environment is in proper condition just prior to the final quality assurance inspection. We therefore want to delay clean worksite so that it concludes the end of day, and just before the final inspection. This scenario is best achieved by changing the primary constraint of clean worksite from ASAP, which is the default, to ALAP.
The ALAP primary constraint on clean worksite expends the one day total float of clean worksite, so that it concludes immediately before to the final inspection. Note that clean worksite and final quality assurance inspection have a Finish to Start (FS) relationship.
There are two ways to make the update to the clean worksite constraint. The first way is to choose the clean worksite activity and select the general tab in the bottom details, Figure 2.
In the constraints frame choose As Late As Possible from the drop down primary constraint menu. Another way to make the change is directly on the activity table. This way assumes that the primary constraint column is displayed in the activity table. If it is then simply select As Late As Possible from the drop down primary constraint menu for the clean worksite activity, Figure 3.
It is important to note that ALAP constraints do not require a constraint date. That is because we are not specifying a specific date for the clean worksite activity. We are simply telling the scheduling software to deplete the total float of the clean worksite effort. Its total float then becomes zero, as displayed in Figure 4, after recalculating the schedule.
In most schedules the narrative is to perform the effort as soon as logic permits. This is when it is appropriate to use the ASAP constraint, which is the default in Primavera P6 EPPM. There are situations though when you want the effort to commence as late as logic permits, but without compromising the schedule completion date. To achieve this scenario, Primavera P6 EPPM provides the ALAP primary constraint. Although not as popular as the ASAP constraint the ALAP constraint is never-the-less a handy tool in the Primavera P6 EPPM toolkit.