Primavera P6 has quite a few different constraints that you can apply to an activity. Of these, you can consider them to be either hard or soft constraints, as we’ve discussed before. There’s one Primavera P6 constraint however that can be very useful in certain situations, but it doesn’t seem to fall into either group. Let’s explore the As Late As Possible constraint.
Setting an As Late As Possible (ALAP) constraint on an activity can be used to avoid delay between the finish of an activity and the start of its succeeding tasks.
If an activity has an As Late As Possible constraint, it will behave in the following way:
- The As Late As Possible constraint will schedule the activity to start as late as possible – this means if the activity has positive free float (a natural delay between the activity’s finish and the start of it’s successor, not a lag), Primavera P6 will force the free float delay to be 0.
- The As Late As Possible constraint it will not affect the start or finish dates of any succeeding tasks. If succeeding tasks move backward or forward in the plan the task with the As Late As Possible constraint will automatically schedule itself to start as late as possible.
- As Late As Possible constraints work differently in MS Project. Project will actually delay the start of successors when an As Late As Possible constraint is applied.
Let’s see the As Late As Possible constraint in action in Primavera P6:
Consider the Start Milestone “Delivery” below.
Here I have changed applied the As Late As Possible constraint (with a lag of 10d ). Notice on the Gantt Chart how the Delivery milestone has shifted quite far into the future to start 10 days before the Drywall activity.
The idea is to die young as late as possible.
– Ashley Montagu
Example “Procurement” Activities
An example use for the As Late As Possible constraint is in a project that has procurement of materials. The procurement of materials have to precede the task that they are required for. Usually projects are not driven by the procurement tasks so there will be a delay between the finish of the procurement and the start of the task that requires the materials (not usually desirable situation). By adding As Late As Possible constraints to the procurement tasks they move forward until they finish at the start of the task that requires them.
This will help to have a positive cash-out flow and materials will not be on site until they are required (Be aware that they are not late ! give some buffer).
Example “Drawings required by” Activities
Before something can be constructed, drawings are often required. These drawings are often required a specified period of time before the commencement of the task that requires them. Using an ALAP constraint will allow the task to be scheduled to be always a fixed number of days prior to the start of this task. To do this link tasks together with a finish-to-start relationship and apply a 30 day lag. Then assign an As Late As Possible constraint to requirements of drawings task.
Using As Late As Possible constraints in Primavera P6 can help you more accurately model the scenarios in a project. Go and experiment with them.