Blog Title
Published June 2021, Updated April 2023
Published January 2023, Updated July 2024
How Calendars can Make or Break your Schedule : Scenarios and Examples
In this article, you’re going to learn what schedule calendars are, what they look like with examples, and through a variety of scenarios understand the calendar importance for an accurate and reliable schedule.
If schedule calendars aren’t created or applied correctly, they invalidate schedule accuracy. The schedule may become no longer feasible by being overly optimistic, and unreliable.
These situations happen when the person preparing the schedule lacks an understanding on how schedule calendars work and the consequences of not having them set up and assigned properly.
Schedule calendars can make or break your schedule. Everything else in your schedule could be compliant with your contract and industry best practices, but if the calendars are incorrect, it compromises the entire schedule’s accuracy.
In the sections below, we discuss:
o Military and Federal Requirements for Schedule Calendars
o What are Schedule Calendars?
o P6 Schedule Calendar Examples
o Scenarios: How Calendars can Make or Break your Schedule
o Summary
Source: UFGS 01 32 17.00 20, Updated May 2018
Source: UFGS 01 32 16.00 20, Updated August 2018
From 01 32 17.00 20 (Cost-Loaded Network Analysis Schedules / NAS):
Source: UFGS 01 32 01.00 10, Updated Februay 2015
Construction schedules for military and federal projects are required to use schedule calendars that block out the days specified in the contract, such as weekends, federal holidays, and weather days.
The snapshots below are taken from the standard UFGS scheduling specifications that are used for various agencies, including USACE, NAVFAC, AFCEC, NASA, and the VA.
From 01 32 01.00 10 (Project Schedule)
Military and Federal Requirements for Schedule Calendars
What are Schedule Calendars?
Schedule calendars are created within the scheduling program, such as Primavera P6, and allow the user to define working days and hours for each calendar.
Every schedule activity needs to have a calendar assigned. That calendar assigned determines which days that activity can take place.
Example 5-day weather calendar with anticipated adverse weather days blocked out
A 5-day weather calendar (5DW) calendar is a copy of the 5-day calendar, but includes additional days blocked out for anticipated adverse weather.
The number of days that need to be blocked out is typically included in the scheduling specification but can also be located in other parts of the Division 01 specifications, or another part of the contract.
Example 7-day calendar with no days blocked out
P6 Schedule Calendar Examples
The white days below are work days, and blue days are blocked-out weekend and federal holidays.
Schedule calendars applied incorrectly to activities
Schedule calendars that are applied to the wrong activities lead to faulty start dates, finish dates, and total float – compromising the overall accuracy of the schedule.
Scenario 3: The calendars are applied to the wrong activities.
Lastly, this scenario applies to schedule activities that are assigned to the wrong calendar.
The snapshot below shows the that testing the underground plumbing is assigned to the 7-day calendar. As described above, this calendar allows activities assigned to it to take place over the weekend or federal holidays.
Since this work can’t take place then as required per contract, the highlighted 04-Oct-23 finish date below isn’t realistic. The 0 days total float is also not realistic, and more likely is several days negative.
The backfill and compact activity is also assigned to the 5-day calendar instead of the 5-day weather calendar, so it doesn’t take into account any anticipated adverse weather. Not only would this activity be taking place later because of the incorrect calendar assigned to its predecessor (testing the underground plumbing), but it may also finish at a later date due to the wrong calendar assignment.
Example 5-day weather calendar missing anticipated weather block-outs
In a similar scenario as described above, weather calendars that are missing required blocked-out days also present an overly optimistic and less realistic schedule.
The snapshot below is for an example project in an area with moderate to severe winters. The calendar blocks out weekends and federal holidays but is missing the required (example) 6 work days of anticipated adverse weather as required per contract.
Any weather-dependent activities assigned to this calendar (sitework, excavation, foundation, etc.) are therefore going to be shown this month as taking place every work day in this month.
This calendar assumes there will be zero days lost to weather in an area with moderate to severe winters during the month of January. This also creates an overly optimistic and unrealistic schedule.
Example 5-day calendar missing weekend and federal holiday block-outs
Scenarios: How Calendars can Make or Break your Schedule
Now let’s illustrate the importance of schedule calendars on your schedule and what can happen if they’re incorrectly created or applied.
Scenario 1: The schedule calendars don’t block out required non-work days.
If the schedule calendar is missing the required blocked-out days, it’ll show activities taking place when the contract doesn’t allow.
For example, the snapshot below shows the 5-day calendar for the month of May that’s missing weekend block-outs and the Memorial Day holiday. Any activities assigned to this calendar will show work taking place on the highlighted weekends and federal holiday.
This can result in an overly optimistic schedule, or work that realistically couldn’t take place at the rate it’s shown. If the contractor doesn’t work those 4 weekend and holiday days highlighted below that are missing as block-outs, the work will fall behind 4 days that month.
Now consider if every month were missing days that needed to be blocked-out for the duration of the project – this effect compounds.
Schedule calendars that don’t block out required non-work days are overly optimistic with productivity, and therefore less reliable.
Schedule calendars are created within the scheduling program and allow the user to define working days and hours for each calendar that’s created. Each activity has to have a calendar assigned.
3 common schedule calendars include:
- 5-day work (5D) calendar: Typical workday calendar that blocks out weekends and federal holidays as non-work days.
- 7-day work (7D) calendar: Shows work taking place every day of the week, with no days blocked out.
- 5-day work weather (5DW) calendar: A copy of the 5D calendar, but with additional days blocked out to account for anticipated adverse weather.
Errors in creating or applying the schedule calendar can result in the following scenarios:
- Schedule calendars that don’t block out required non-work days -> Overly optimistic productivity.
- Schedule calendars that don’t account for anticipated adverse weather -> Unrealistic weather expectations.
- Calendars applied to wrong activities -> Inaccurate schedule output such as activity start dates, finish dates, float values, and overall schedule accuracy.
Questions or comments? Reach us at connect@cpm-ss.com.
Thanks for reading.
Related Resources:
How to Learn Primavera P6 Quickly: A Beginner's Guide
Why Quality Construction Schedules Matter
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This blog is for general informational purposes only and is not to be considered an official interpretation or enforcement policy of the UFGS standard specifications. As individual project requirements vary, refer to your specific contract. See our Terms and Conditions and Disclaimer for additional information.
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