Construction Scheduling. Too much Detail.

When we develop the Baseline CPM Schedule for a construction project, we need to develop the WBS to establish the project deliverables.

To what level of detail is this required?

The general idea is to decompose the project deliverable down to the Work Package level. For construction, this could be taking the WBS down to an area of structural foundation for a large project. It is really taking the deliverable down to the point that it can be easily identified and measured.

We then develop the “work” activities that need to happen to produce this deliverable.

Basically, we develop the list of activities, sequence them, assign the resource(s) and determine the Activity Duration, and assign the activity’s Budgeted Cost. There are also the Activity Code, Calendar, and Role assignments…

Many specifications have limits on the number of Work or Calendar Day duration a “work” activity may be assigned. A good rule of thumb is “not to exceed the reporting period”. I like to cap my “work” activities at 20 Work Days or less. An activity should only have one responsible party performing the work. If an activity only has one party performing the work and the duration of the work is going to exceed 20 Work Days, perhaps it is best to break the work area down to allow smaller durations. It is difficult to accurately measure the performance of activities with large areas or durations.

The use of activities with large Activity Durations also leads to the use of Start-to-Start and/or Finish-to-Finish relationships to model the work which is now running concurrently with other large duration activities. This should be limited. The overuse of Start-to-Start and/or Finish-to Finish relationships is a basic problem for many detailed project schedules. Makes a pretty Gantt Chart, but does not allow adequate control and measurement of scheduled work.

Most deliverables should have activities with durations much less than 20 Work Days. They should not all be 1 Work Day unless that is actually what it takes to model the work of several parties. Usually, the “work” could be broken down to 5 days to excavate the foundation, 2 days to install reinforcing steel and any vapor barrier or blockouts, and 1 day to place concrete and an activity with a period of time for concrete curing. Breaking the work down to this level allows the work to be easily measured and managed. Too often I see a “Place Foundation Concrete” activity with a duration of 10 Work Days. No cure activity. No idea if cure time is included or not…. No idea when the excavation should complete or when the reinforcement placement starts…. Most likely, the formwork and reinforcement work will run concurrently at some point and the concrete placement will be driven by the finish of the reinforcement work and inspection. If there is a delay in delivery of reinforcement steel, we should be able to accurately model that…..

The idea is to develop a schedule which is manageable and has enough detail to control the work. Pretty simple.

If there is more than one contractor performing the work, you probably need to break down the work further. If a series of activities are all running concurrently, perhaps it would be best to break the work down into smaller areas. The goal is to use Start-to-Start and/or Finish-to-Finish relationships as little as possible. Using Finish-to-Start relationships is almost always the best way to model the work. This usually requires breaking the work down into smaller pieces…

I’m sure many of you have comments or additional insight into this subject. Please share!

I’d love to hear what you think!

Please visit https://conschmanservices.com to learn more about Construction and Schedule Management Services, LLC

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Please visit my “The Blue Book” ProView.

Paul Epperson CCM, PMP, PSP, PMI-SP

Construction Scheduling. Let Durations Help You.

How can you use the Activity Duration value to help you manage your schedule?

Simple, just look at all the columns and do some math in your head.

When your contractor develops the project baseline schedule, they develop the Original Duration for each activity. How they develop the durations is a subject for another post. But let’s assume they have used historical data, input from subcontractors, calculated productivity and quantities, or some method of developing an accurate value for the each Activity’s Original Duration.

Most Schedule Presentations (Gantt Chart pdf’s) have the activity names, dates, a percent complete and a duration for each activity shown in columns. Then there are the magical bars to the right. Sometimes there are even relationship (logic) lines drawn from activity to activity so you know what drives what, right? Can you actually read it? Doubtful…. Anyway, let’s focus on the duration columns.

If you’re looking at a Schedule Presentation from a Primavera P6 schedule, there are options for which duration columns you can see. Almost everyone uses the Original Duration column. Most of us use the Remaining duration column. That’s all we need to know, correct?

Not really, there is a column that shows the At Completion Duration. This is not seen in presentations that often, probably because we want more room for the magic bars and lines… But this is an important column to be able to see when reviewing a Schedule Presentation pdf.

If you have an Original Duration of 5 days (Work Days or Calendar Days depends on the Calendar. This is a subject for another post), and a Remaining Duration of 3 days and the percent complete (whether it is Physical, Duration, Activity, Performance, or Cost or another type is a subject for another post), is 50%, things are looking good, right?

Not always. If you look at the At Completion Duration, you may find that while the Original Duration is 5 and the Remaining duration is 3. But the At Completion Duration could be 35 or any other value if the activity finish date is riding the Data Date. This can happen depending on the settings used to manage the schedule. Unless you actually look at the dates and do some calculations in your head while reviewing the schedule, when you don’t have the At Completion duration column to use, you may not see the slippage.

Ask your contractor to display the At Completion Duration column for their Progress Meeting Look Ahead Schedules and any other pdf submission. It’s worth the trade off with the magic bars and lines!

Knowing what was planned, what is remaining and what the time impact of activity progress slippage is can save you some trouble.

I know many of you can offer additional comments and recommendations. 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!

Please visit https://conschmanservices.com to learn more about Construction and Schedule Management Services, LLC

Please visit my LinkedIn account to learn more about me.

Please visit my “The Blue Book” ProView.

Paul Epperson CCM, PMP, PSP, PMI-SP

Construction Scheduling. The problem with Start to Start Relationships. Or, Why doesn’t a Delay to this Activity Duration push my Finish Date?

person-question-300x300Do you regularly use Start-to-Start SS relationships? Perhaps you add a lag to drive the start of the successor out a few days?

Have you had problems with this practice? Perhaps a delay to the completion of the predecessor activity is actualized, but does not impact the schedule?

This is a common practice, unfortunately. The best practice is to add an additional successor with a Finish-to-Start FS relationship, or even a Finish-to-Finish FF relationship. This will provide the logic that allows the delay to the completion of the activity to drive other work. Without that additional successor activity, what you have is an “open end” and the activity finish does drive any successive work. It could never complete and you would not see the problem in the logic.

This condition is simple to prevent. Just make it a practice to always add a FS or FF successor when using a SS relationship. The problem usually happens when you’re trying to recover time and start to schedule work concurrently. You simply forget to add the additional successor….

Personally, I like to develop my schedules with all FS relationships unless the plan actually calls for a SS condition. If I have the need to use SS relationships, I assume my work isn’t broken down into enough detail to allow me to sequence the work logically.

There are always “exceptions to the rule”, but this is one I try to follow.

What other methods have you found to successfully utilize SS relationships, with or without lags?

I’d love to hear what you think!

Please visit https://conschmanservices.com to learn more about Construction and Schedule Management Services, LLC

Please visit my LinkedIn account to learn more about me.

Please visit my “The Blue Book” ProView.

Paul Epperson CCM, PMP, PSP, PMI-SP

Construction Scheduling Terms. What is the “Data Date”? What is “OOS”? What are “Lags”?

Pert P3You are working with a construction scheduling consultant and they use terms you’ve heard before, but you’re not 100% sure you really understand what they mean.  More importantly, you’re not sure how they affect the schedule.

Do not be ashamed, why should you have any in depth knowledge of yet another specialized function of the project management process? That’s why professional planning and scheduling consultants exist!

What is the “Data Date” and why do I care?

The data date is simply the “as-of” date used for progressing the periodic schedule update.

Typically, the data date is the end of the month, but I’ve seen it be the 15th and the 25th. Each schedule specification is different based on the owner’s requirements for reporting. Note: MS Project uses the term “Status Date”.

This is the date that all progress should be updated for progress up to. Everything after the data date is the pan to execute the remaining project activities. There should never be work in progress or incomplete with dates prior to the data date. I’ve seen this all too often with schedules run in MS Project because the person doing the schedule update does not understand this concept and how to adjust the settings to force incomplete work to move to the status date.  It’s a simple fix for an experienced scheduler. Always look at your schedules and know the data date and verify all work prior to the data date is complete and all work after the data date shows no progress. Think of the data date as the starting off point for the rest of your project…. This is a necessary practice for construction scheduling.

What is “OOS” and why do I care?

OOS or Out-of-Sequence is simply a way of saying that work actually completed did not progress as scheduled.

Typically, this involves an activity that was scheduled to start immediately after the finish of it’s “predecessor” having actually started prior to it’s “predecessor” finishing. Other reasons may be work progressing much differently than scheduled or work being suspended for whatever reason.

Why do you care? You care because this logic is still driving any “successor” activities and is not correct based on how you actually completed the work. It affects all downstream work logically tied to the finish of the OOS work and does not model the remaining work correctly.

This can affect change order fragnet insertions, not produce correct total float values, and does not provide you with an accurate as-built schedule. Best practice is to correct the logic for OOS work immediately after updating the progress each period update. Most schedule consultants do this, but many do not and most PM’s and Superintendents do not. Many owners are not aware of the need to correct OOS relationships and do not require or enforce this practice. This is unfortunate. There are times y0u can leave some OOS relationships in place, but absolutely OOS work on the longest path or near critical path should be correct. Most construction scheduling consultants correct OOS relationships each schedule update.

What are “Lags” and why do I care?

Lags are like invisible activities added to the schedule; which typically separate start dates of successor activities by a set amount.

Depending on which calendars are assigned and the relationship selected, a current activity’s successor activity will start immediately after the finish of the current activity, if the relationship is a Finish-to-Start, FS relationship. Adding a lag of 3 to this relationship would force the start of the successor to wait 3 work periods until starting.  Sometimes this is used for concrete curing time…… I prefer to use an activity for this so the time is transparent.

But typically, lags are used with Start-to –Start, SS relationships to allow work to be schedule concurrently. The lag forces the successor activity to wait set number of work periods after the start of the predecessor activity starts before starting. This models a plan to start one piece of work and then start successive work a set duration later. Such as finishing gypsum board wall sheathing before the entire area covered by the activity to hang the gypsum wallboard has completed. This is fine if this represents your plan to execute this work. Unfortunately, this is also how most PM’s and Superintendents choose to get the scheduled finish date back on time after the periodic update shows the project is behind schedule. This is still fine if the work can actually be executed this way, and it is the actual plan to “recover” lost time. It is just so darn easy to do, that many times it is used to appease the owner only and no plan is used to actually accomplish the work concurrently. This happens when the schedule is only part of the invoice process, and not an integral part of the project management process.

Don’t be afraid of lags, but the use of lags should be judicious and justifiable. There are many ways to model the logic to reduce the number of lags used. Typically, breaking the work into smaller pieces will allow the work to be scheduled without the use of lags.

Negative lags are bad idea and should be avoided or disallowed. There are many ways to make the logic work without the use of negative lags. Most schedule consultants stay away from negative lags.

MS Project shows lags and relationship types other than Finish-to-Start, FS in the predecessor and successor columns. Primavera P6 does not. Although it is not always easy to understand the effect a lag is having on the schedule, you should always be aware of their usage and understand the effect they have on the project schedule.

When in doubt, seek out the advice of a professional planner and scheduler.

Please visit https://conschmanservices.com to learn more about basic schedule concepts.

Please visit my LinkedIn account to learn more about me.

Paul Epperson CCM, PMP, PSP, PMI-SP