Construction Scheduling. Checking the CPM Schedule for Lags/Leads and Relationship Types.

In my previous post, I provided some basic schedule quality validation methods for use by project management professionals without access to, or proficiency with Primavera P6.

Continuing this area of discussion, this post will cover relationship lags, leads, and relationship types. This is a sore subject and there are typically many problems found in this area.

Again, when someone hands you the schedule update Gantt Chart, how do you know that the plan is valid? How can you do a quick validation of the schedule for basic requirements?

As I said before, a pdf of the schedule is nice for meetings, but someone from the owner’s and the contractor’s project teams needs to verify the schedule quality. The contractor usually has an in-house scheduler, so this is part of their processes during the development, update, and revision processes. What about contractors using a third-party planning and schedule professional? How do you validate our work? What about the owner and their construction management agency? How do they validate the schedule as presented by the contractor?

The owner and CMa will require the schedule in native format. That will allow their planning and schedule professionals to use the schedule program and verify schedule settings and structure. This is a must. I still see owners who simply look at the pdf and hope the schedule slippage will stop, one day….

Simply reviewing the schedule log generated by Primavera P6 will let you see the open relationships, out-of-sequence relationships, schedule settings, constraints, and other information.

You will not, however,  be able to find the relationship types and lags/leads used. One word of note here, I personally, do not use leads or negative lags. This is my preference. That said, you need to know how the logic is structured to know why it flows across the Gantt Chart layout the way it does. Just because the dates make sense does not mean that the logic is valid.

You can require the contractor provide you with a logic report from Primavera P6. This can be run sorted on activity ID. You can also have the predecessor and successor columns shown. The recent version of P6 will also show SS or FF relationship information, (with lag durations) much like MS Project does. Older versions of P6 do show relationships or lags/leads in the predecessor and successor columns. The logic report does. It just requires you to use the report as a legend while looking through the schedule layout to verify predecessors, successors and lags/leads used. This is very tedious, but this is a good practice. There are third party software programs that will produce reports only showing the activities with relationships other than FS. You can also produce this report in P6. But you must know how to do so…

The use of SS or FF relationships and limits for their us is a bit of a hot topic among planning and schedule professionals. Many organizations and government agencies include requirements in their schedule specifications limiting the use to a percentage of the total relationships. Many specifications do not speak to the use of relationships at all. I personally severely limit their use during development and only grudgingly use them when I do.

I avoid lags, but I do use them to push submittal development activities out to stagger the process. I do not use lags for concrete curing or other non-work activities which drive successor activity starts. These should be activities and transparent to all users of the schedule.

When reviewing the schedule for the use of SS, FF relationships and lags, simply make note of the usage and decide for yourself if the logic could be better modeled by breaking the activities into smaller areas or processes to allow the use of FS relationships. This is always the best approach. Review the use of lags the same way. If the activities can be broken down into more detail to allow the use of FS relationships for the work process, that is your best choice.

You can’t review or validate any of the information above if you don’t have the information in a format that allows you to analyze it. Require the P6 logic report or use third party software or learn how to find and analyze this information using P6 yourself. It is basic schedule mechanics, but the logic, relationships and activity durations are the backbone of the schedule. If the schedule isn’t developed following the project schedule specifications and schedule best practices, it is very doubtful the schedule will be a valid tool for the planning or control of the project performance and management.

These are just a couple of additional items that form the basics…. There are other items worthy of validating and I will speak to these in future posts.

I know many of you already know this information and can offer additional guidance and support, for all of us. I welcome your comments and input. My goal, as always, is to help our industry and help the projects we support….

I’d love to hear what you think!

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Paul Epperson CCM, PMP, PSP, PMI-SP