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  • Pam Scholefield

The Critical Path-Just How Critical Is It?

You’ve probably heard the term “Critical Path” many times.  But, but what does is it really mean and how critical is it? 

 

The standard

Nearly all courts recognize what is known as the Critical Path Method (“CPM”) as the most readily accepted method of measuring project delays. CPM is the benchmark that is universally accepted in construction delay claims litigation. It is extremely important for anyone involved in construction to understand how CPM is used for proving delay claims.  If you don’t know how a delay is measured, you may find it difficult proving you were really damaged by a delay. Or worse yet, you may find it difficult defending yourself against an unsubstantiated delay claim.

 

A quick history

Commonly known by its initials “CPM”, it is a method of estimating how long a project will take to complete.  A critical path is determined by taking the all the key tasks in sequence of which task has to be completed before and after each other task, and then determining which series of tasks  up the longest time necessary to complete the entire project. The procedures are the same for small projects or large projects, but larger projects will benefit from the use of project management software, since the software can handle hundreds of tasks and variables with ease.  

 

The basics

Here is a quick primer on what it takes to create a CPM schedule. CPM is focused both on time and sequencing.  First, determine the tasks needed to complete a project.  Then, put each task in the sequence it needs to be performed and assign each task the duration required to complete it.  Tasks that are dependent on other tasks to be completed will be the types of tasks that end up on the critical path.   You need to know the following information in order to create any sort of CPM schedule:

  1. Specific activities:  These are unique tasks that have a distinct length of time for completion. In construction, these are usually straightforward and fairly easy to identify by trade.

  2. Milestones:  These are events that identify the beginning or end of a task or set of tasks.  They are often important interim goals achieved before completion of the entire project.

  3. Sequence:  Getting from bare earth to a finished building requires the proper sequence of construction tasks.  Some sequences are obvious, and others are not, for example it is clear that earthwork must come before roofing.  But, it may not be so obvious whether or not finish plumbing would come before or after roofing, or whether or not it can be done in its own independent timeframe so long as it is done by the time the rest of the project is completed. 

  4. Dependent Tasks: Careful analysis is often needed to determine the cause and effect relationships between tasks.  Tasks that depend on the completion of another task must be identified.

  5. Time Estimate:  The time required for each activity is needed.  An experienced estimator can shoot from the hip and use past experience as their guide, but often input from each trade subcontractor is needed to get realistic estimates of time for their work. 

 

 

The path to completion

With the above information available, a project schedule diagram can be created.  Laid out graphically, all the tasks are displayed together to visualize the entire project from beginning to end, with some running simultaneously, some depending on the completion of a prior task, and some having their own path independent of other tasks. The critical path would be the longest duration of dependent tasks that must be done in sequence in order to get from the beginning to the end of the project.  There may be tasks that can be performed at any time after achieving a certain milestone but have no specific start date, only a required completion date. The difference between the time allocated to perform the task and the actual duration of the task is commonly known as float or slack time.  The tasks on the critical path have no float time because if they are delayed, then the entire project completion would be delayed.  Also, a task that does have float, may end up on the critical path if it is delayed past the float time.   If you are a subcontractor and your work is on the critical path and you are unable to complete your work by the time allocated on the project schedule, you will most likely be charged with delay damages, which often are in the form of liquidated damages.

 

The real world

Once a project is planned out and a critical path defined, there is no guarantee that the course of the project will actually follow the plan. A few examples of why this can happen are: 

  • Estimates:  One of the simple reasons for a schedule deviation is that everything is based on estimates.  The schedule is only as good as the quality of the estimates, and for the most part, the people who created the estimates are not the people who actually perform the work.

  • Changed conditions:  If the actual conditions are different from those expected at the time the estimates were determined, the estimates may not be realistic.

  • Change orders:  Almost without exception, projects will have change orders.  What needs to be considered very carefully is whether or not the change orders affect just a specific task schedule or the critical path.

 

Making CPM work for you

Keep in mind though, just because there may be change orders, changed conditions, sloppy estimating or anything else that causes a delay, if the delays do not affect any of the critical path tasks, the project as a whole, is not delayed.  Also, applying additional resources to activities that are not on the critical path may allow them to be completed early, but it won’t benefit the overall project end date. And, if your work is not on the critical path at the beginning of the project, it may end up on the critical path if you cannot perform it during your allocated time on the project schedule.

 

The bottom line is that you need to be able to analyze whether your work is on the critical path.  If it is, and it is delayed, you’ll be the one blamed for a delay in the completion of the entire project – and that’s pretty critical!

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