Month: March 2017

Construction Scheduling. Use of Relationship.

When your contractor develops the project baseline schedule, do they use many Start-to-Start (SS) or Finish-to-Finish (FF) relationships? Do you know?

A relationship determines how the successor activity will start or finish relative to the predecessor activity. The most common relationship is the Finish-to-Start (FS) relationship. The scheduled finish date for Activity A determines the scheduled start date for activity B. Unless a lag is assigned, this is simple. (See previous post).

However, often the schedule model requires the use of SS and/or FF relationships. If the activities will actually run concurrent and the activities are broken down to the level of detail necessary to plan and manage the work, this is acceptable. If the relationship includes the assignment of a lag, it may still be acceptable but this relationship should be reviewed and agreed to by all parties.

The problem arises when the series of work activities is developed with SS relationships and there are not any successors to the finish of these activities. These are essentially open ended relationships which means the activity could not finish and still not affect the schedule. This may indicate the work is not developed to enough detail to allow Finish-to-Start (FS) relationships to drive the work. Or the addition of work driven by the activity was missed during schedule development. If this work happens to fall on the Longest Path, this path is now driven only by the start of work for each activity, not by the finish of the work for the activity. In time, these relationships may fall on the Longest Path through updates and out-of-sequence work. personally, I prefer to limit the use of SS relationships in general.

Then there are the Finish-to-Finish (FF) relationships. These force the successor’s scheduled finish date to push out to follow the predecessor’s schedule finish date. This is commonly used to close off SS relationships to model concurrent work with the finish dependency. However, often the only successor is the FF relationship. This creates an open finish, which is much like a missing successor. If the predecessor has only the finish of the concurrent activity to drive, and this relationship is a FF relationship, and the successor has no other predecessor. It effectively has no predecessor to the start of this work. If the predecessor activity has only the successor with a FF relationship, what future work does it drive?

Finally, there is the combination of relationships that create reverse logic. Activity A is a FF to Activity B. Activity C is a SS to activity B. The duration of activity B determines when activity C can be scheduled to start. The start of activity B is not driven by any other work. The finish of activity B is driven by the finish of activity A. If the duration for activity B is increased, unless the start of activity C is driven by another predecessor relationship, the start date for activity C is pulled back to schedule an earlier start. This can have unintended consequences for the schedule. We see this often when the schedule is developed using a lot of SS and FF relationships.

We won’t mention the Start-to-Finish (SF) relationship. This is extremely rare. This says that the start of a predecessor cannot start until the finish of the successor. I have only seen it used intentionally and with an acceptable reason twice. And that was to model work on a rolling wave schedule for which there was not much design detail developed. However, this relationship is sometimes used by mistake.

The SS or FF relationship, if used correctly, can allow the schedule to model the plan. It is my opinion that the use of these relationships should be kept to the absolute minimum and be only used to model actual planned concurrent work which is broken down into the level of detail necessary to plan and control the work.

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. Use of Relationship Lags.

When your contractor develops the project baseline schedule, do they use many relationship lags? Do you know?

A relationship lag is an imposed period of time between the predecessor and successor activity. A common use in a Start-to-Start (SS) relationship with a 2-day lag. Perhaps the contractor’s plan is to start finishing drywall 2 days after the drywall installation begins. This allows the work to run concurrently.

There absolutely are times when work can and should be modeled this way. However, care should be taken to ensure an open start isn’t inadvertently created. (This is a future topic)

The problem arises when the series of work activities is developed with SS relationships with an assigned lag. This may indicate the work is not developed to enough detail to allow Finish-to-Start (FS) relationships to drive the work. The issue is, once the start of the predecessor is actualized, the start of the successor is only dependent on the calendar set for use for lags. This may not match the number of days intended. If this work happens to fall on the Longest Path, this path is now driven by a calendar. I prefer to limit the use of SS relationships in general, much less with assigned an assigned lag.

Then there are the Finish-to-Finish (FF) relationships with lags. These allow the successor work to finish only after the predecessor’s finish date plus the lag duration. This is commonly used to close off SS relationships to model concurrent work with the finish dependency. However, often the only successor is the FF relationship with the lag. This creates an issue in itself. (This is a future topic)

The most serious issue is when the relationship is an FS with a lag. What does the lag model? Should there be an activity to establish this difference in the relationship finish to start? Most likely, the answer is yes. There is nothing wrong in using an FS with a lag to have the lag represent say, cure concrete. I personally prefer to add the cure concrete activity with the number of days required. This is more transparent. The lag is not visible and creates a non-work period seen in the Gantt Chart bars and can cause confusion.

Then there is the negative lag, or leads. Many schedulers like negative lags and use them as a viable way to model the plan. When I see an FS relationship with a negative lag, I wonder why the use of a SS relationship with a positive lag could not have been used. The use of the negative lag may better represent the thought that the successor cannot start until 3 days prior to the finish of the predecessor. And this 3 days is the critical period. I personally prefer to model this type of plan with a SS with a lag or to further break down the activities to allow the use of FS relationships to model the work.

Finally, there are the SS relationships with an assigned lag that is larger than the activity duration forcing the model to show the work as an FS relationship. Why not just use the FS relationship? Unless there is a reason to model the work this way, it just doesn’t make sense to do so.

The relationship lag, if used correctly, can allow the schedule to model the plan. It is my opinion that the use of lags should be kept to the absolute minimum and only used to model SS or FF relationships.

But remember, the lag follows the calendar set for use for lag calculation. If the predecessor calendar is set for use, and the predecessor is assigned to a 5-day work week calendar, the lag will follow that calendar and the duration will be in work days. So, a 3-day lag could become a 5-day delay between the relationships if the lag spans a weekend. This may not have been the case when project work was planned and the schedule was developed and the lag did not span a weekend. Remember, this is not transparent, only someone who understands the schedule software and has access to the native file format can verify this. Unless the schedule layout includes the columns which show relationships with lags and the column that shows calendars. Even then, you need to know what the actual non-work days for the specific calendar are.

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. Do you Really Need a Scheduler to Develop and Manage the Schedule?

Does an experienced contractor really need a professional scheduler to create the baseline schedule and manage the update and revision process? Not necessarily, many projects can be scheduled using a worksheet or a simple program to model the activities and bars against a timeline.

But, does that typically provide the best schedule for managing the project? Can the contractor benefit from having a schedule professional on their team? Or at least as a third-party consultant?

Budget constraints, lack of staffing, or bad experiences with project scheduling can be some of the reasons a contractor will not have a scheduler on the project team. And, make no mistake, there is cost to this

I can understand why a contractor may be reluctant to use a professional scheduler, to a point. Some projects are simple enough and can be managed this way. Some owner-contractor relationships are strong enough that both parties trust the other will compensate them for delays or late completion.

What about the projects that really should have a schedule professional supporting the contractor with schedule development techniques, best practices and an understanding of what the schedule specifications actually require? What value do they receive when they have that support in place?

First, they should benefit from having the scheduler review the RFP specifications, prior to submitting the proposal, to review and quantify what the schedule specifications require and assist with the budget for schedule development and management. Many contractors see the specification requirement for a “CPM” schedule and assume it means a “P6” schedule or a fully resource and cost loaded schedule. A professional scheduler can interpret the schedule specification and explain the requirements for the development of the baseline schedule and schedule updates. There is much more to it than most people think there is.

Almost all contractors pride themselves on knowing how they can and will build the project, better than their competitors and for less cost than they budget for. I do not doubt this. I’ve met some great Project Managers and Superintendents and they know how to do amazing things when it comes to coordinating work and managing subcontractors.

But, they are great in their area of expertise. They are not necessarily project controls experts or professional schedulers or cost estimators. Those are specific “trades”, just like being a Carpenter or an Electrician. Most of us in the construction industry can do a little of several “trades”, but we cannot be a specialist in many trades. A few can, but I’m not one of them.

That said, a schedule professional can work with the contractor to put their plan in the program, correctly utilizing the program settings and schedule best practices, to model the plan for use by the entire project team. If done correctly, with input from all the trades and the owner, the schedule becomes a map to the completion of the project.

The schedule professional provides this map with the quality and integrity to be accepted by the owner and used to manage the subcontractors, submittals, procurement, deliveries, mobilization, and the coordination of work. The schedule also provides the Project Manager the ability to manage change order impacts to the schedule and measure performance of the various project team players.

Often, owners require the schedule to be updated and maintained as part of the invoice process. The professional scheduler supports this process by applying the actual progress to the schedule and helping the project team with identifying production slippage and schedule impacts as well as modeling revisions as necessary to revise the plan going forward.

A contractor can possibly manage a project without a schedule professional on their team. But, would they manage a project without field superintendence or materials coordination, or subcontractors for specialized work?

It’s tough to quantify what value a professional scheduler brings to the contractor’s team, but there are definitely costs to not having one. A questionable baseline schedule, the inability to project work with confidence, and the inability to accurately quantify change order delays are only a few basic functions that would be lost.

I know many of you can offer additional comments and war stories, 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!

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