This post continues my series on the various choices available to you when creating a new activity in Primavera P6. The last post covered the various Activity Types available in P6. We learned that there were 5 different Activity Types to choose from when creating a new activity. Today’s post will cover the 4 different Duration Types.
Duration Type choices can be found using the drop-down menu in the details pane of each activity. See Figure 1.
Figure 1
You might notice that each Duration Type begins with the word “Fixed”. Technically speaking, time variables (duration, units, units/time) aren’t truly fixed because P6 will allow you to change them. The intent is for the Duration Type choice to govern which variables change when you adjust the duration of an activity.
1. Fixed Duration & Units: This option means that during planning there is both a fixed number of days and a fixed number of hours that an activity is expected to be completed in.
Let’s consider a scenario where installing the finishes on the 1st floor of an apartment complex is expected to take a finish carpenter 10 days and 80 hours. This means that that the person would need to work 8 hours per day because both the 10 days & the 80 hours are fixed conditions.
In the same scenario, let’s assume that during construction it’s determined that the duration is too long to meet the schedule and needs to be compressed to 5 days. If you reduce the remaining duration to 5 days, the finish carpenter’s 80 labor hours (units) will remain the same but P6 will calculate that they’ll now need to need work 16hrs per day because the 5 days and 80 hours are fixed conditions. The only option is to work longer hours per days. It is now obvious that you will need 2 finish carpenters instead of one to perform this task.
2. Fixed Duration and Units/Time: This option means that there are a fixed number of days that a task will take based on a fixed number of hours worked each day. Let’s consider the scenario where installing the finishes on the 1st floor of an apartment complex is expected to take 10 days with each trade working 8 hours per day for a total of 80 hours. If you select this duration type and then during planning you adjust the remaining duration to 11 days, the remaining hours will automatically adjust to 88 hours because the hours per day (units/time) are fixed and the duration has been changed.
3. Fixed Units/Time: This option is very similar to Fixed Duration & Units/Time when paired with a Task Dependent Activity Type but you might choose this option when you know that you only have 2 carpenters available to you so they can only work 16 hours/day (units/time). This means that if you adjust the duration the units/time will not change, but the total hours will change.
4. Fixed Units: Fixed units operate in much the same way as Fixed Duration & Units when paired with a Task Dependent Activity Type. When paired with a Resource Dependent Activity Type, Fixed Units means that the duration of a task and the number of people you can put on a task is flexible. In other words, you could put additional people to a task or extend the duration, but the total labor hours will always remain the same.
For planning and execution of construction projects I generally recommend using either the Fixed Duration & Units, or Fixed Duration & Units/Time options. This is because on a construction project time (duration) is usually limited, the labor units are usually known and the available labor pool is usually limited (units/time).
One of the best ways to understand which Duration Type will work best for you is to create a dummy activity and change the Duration Type, then adjust 1 variable and watch how the other variables react.
In conclusion, Primavera P6 offers a variety of activity types and duration types that allow users to effectively plan and schedule their projects. Understanding the differences between these types can help prevent unexpected results in your schedule.
If you have any questions or comments, please feel free to reach out!
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