The development of Primavera P6 calendars for your project is a critical part of your schedule development effort. This is really part of the planning stage of developing your schedule. During the planning phase, the project team should be deciding what work periods they are allowed, or plan to use. Also, they should be determining the basic sequencing of work deliverables, building the organizational structure, defining the required and desired milestones, and developing the Project Execution Plan with the Schedule Control Plan.
Any Work Day (WD) duration you establish for the activities, as well as the project, will be affected by the activity calendar assignments.
For example, in Figure 1, activity S-01-FR-1050 Install Exterior Siding S-01 has a 20 WD duration with a 5-day week Holiday & Weather calendar assigned. However, the projected Calendar Day (CD) duration is 35, (22Nov19 – 27Dec19). This activity spans the period of the project with Thanksgiving and Christmas as well as having non-work days blocked out for the anticipated weather.
If this activity were scheduled to start late July, the CD duration would become 31 as shown in Figure 2.
This is also a good example of why we need to break activities down to small durations, less than 20 WD’s. Once we add in the non-work periods, the activity becomes more difficult to control / measure.
The WD and CD duration can vary greatly and will do so, the larger the WD duration is. With this in mind, once you start adding activities and logic ties, we all start looking at the dates for the project. If the correct calendars are already developed and assigned, the dates we see are more likely to be accurate.
That said, I prefer to develop my P6 calendars prior to the development of my Work Breakdown Structure (WBS), activity coding, resources, or activities.
Typically, for an average construction schedule, I develop a group of calendars shown in Figure 3, which cover most needs.
I prefer to work with Project Level P6 Calendars. This is because, once I set them up, any changes I may make to a Global Level calendar will not affect my Project Level calendar, if I have set the “inherit holidays and exceptions from Global Calendar” to <none>. (See Figure 4).
This also keeps anyone else importing the schedule with default settings from importing another Global Calendar into their database.
I develop a project level 7-day Workweek calendar to use with long lead delivery, summary, Milestone, or Calendar Day, CD required duration activities. (See Figure 4). This calendar simply has every day as an 8-hour workday.
I also develop a project level 5-day Workweek with Holidays calendar for use with submittal, administrative, and non-weather sensitive activities. (See Figure 5). Often, the required holidays are detailed in the project specifications.
If the project has weather sensitive activities, I develop a 5-Day Workweek with Holidays and Weather calendar. (See Figure 6). Some project specifications list the non-work days for weather. Most do not. Some reference using the 5-year average based on the National Oceanic and Atmospheric Administration, NOAA for the area your project is located. When the specifications do not list the non-work days for weather, I prefer to use the NOAA 5-year average.
If the project has any other anticipated non-work periods, it is best to develop a calendar for these at the start of the project as well. Examples of these non-work periods could include:
- planting season for landscape
- cold weather period for asphalt work
- extreme cold or heat for finishes or materials
- wind for crane operations
If the project Team plans to use a 6-day or 4-day workweek, I just develop the above calendars with the appropriate workweeks.
I also develop my Resource Calendars for shift limits or availability of resources at this time.
The assignment of calendars to specific activities greatly determines the CD duration of the activities, and the project. If this work is on the longest path, the projected milestone or project finish date will also adjust accordingly.
By developing the activity calendars during the planning phase of your schedule development, you will not have to worry about missing calendar assignments or creating new P6 calendars. This will become more important when you start the inevitable process of adjusting your baseline schedule to meet contractual requirements. This process will be much easier and more accurate.
Plan your schedule….
Paul Epperson CCM, PMP, PSP, PMI-SP
Paul has extensive experience as a Construction Manager. Over time, he became convinced that there is a critical shortage of skilled planning and scheduling professionals in our industry. In 2009, he backed away from his work as a Construction Manager and began focusing on planning and scheduling. He now serves our industry as a subject matter expert in this area.