A construction project is one of the most difficult tasks one can undertake.  And that is true whether it is building a structure from scratch or renovating an existing structure.  Not only does a builder have to efficiently manage his or her own tasks and business, but he or she is required to work with and supervise a host of other professionals and trades, each of which may have its own agenda, skill set, and schedule.

Consider: a typical construction project will require a general contractor, an architect, an engineer, soil experts, and a host of subcontractors ranging from electricians to plumbers, from drywall contractors to solar contractors, and must obtain building permits and pass building inspections at various stages, which means local government’s own schedule is involved.

And note that the inspections often require precise timing.  Drywall installation will cover up the plumbing and electrical work quite often, thus the inspector, who has his or her own busy schedule, must inspect prior to many of the other trades doing their work on the project.  Project managers must juggle resources, talent, budgets, and expectations to ensure a project’s execution is successful and completed on time. Add to the mix that change orders are almost inevitable on a typical project and the complexity radically increases. This assumes each subcontractor and professional does not become ill or have problems of their own interfering with performance. That seldom happens. 

The critical path method, when done correctly, serves as a guide to help project managers plan and implement the various steps required to complete a construction project.

What Is the Critical Path Method?

The critical path method specifies in time-order the tasks within a project. If those tasks are completed in the correct order and on time, the project can be completed at the anticipated date. It also identifies the tasks that can be completed before or in parallel to critical tasks with more buffer time around them. By prioritizing tasks that have no buffer time and completing other tasks around them, project managers can efficiently keep projects progressing to an on-time completion.

The critical path method offers project managers the ability to stay on budget more easily, schedule talent and resources efficiently, monitor progress, not get overwhelmed with project management demands, monitor, and report on project progress and keep scope creep in check. It also allows them to more easily alter the path when change orders or unforeseen events occur.

For the owner of the project, knowing that the contractor has devised a critical path program is vital to understanding the expertise of the contractor and the likelihood of successful and on-time completion. The owner should review the critical path with the contractor and understand how it works.

The Basic Critical Path Method: 

There are now computer programs that not only assist in creating the critical path but are easily altered when the inevitable changes arise. 

Here is a deeper look into each of these benefits of the critical path method.

1. Better Budget Control

Assuming the project is efficient and timely, one reduces wasted time as trades sit idle waiting for another late trade to finish and one can schedule start dates and end dates with accuracy. This allows the builder to better use resources. One can relocate employees to critical path activities, thereby reducing costly busy work or idle time. A clear breakdown of the project also makes it easier to allocate other resources to the right place at the right time, thereby cutting inventory storage costs.

2. Effective Scheduling

In addition to pulling employees off tasks with lots of float time as needed, project managers can also allocate employees strategically to tasks that have float time. For example, assigning employees who are still going through a learning curve to tasks with float time so these employees may take their time learning new skills. Alternatively, more experienced employees can be assigned to critical path tasks that have little buffer time.

3. Simplified Project Management

Instead of looking at a large, complex project as a whole, the critical path method breaks down a project into the component steps needed to complete it. Project managers can focus on managing a project on a task-by-task basis as the project progresses, making it easier to manage resources, budgets, and talent.

4. Efficient Resource Allocation

The critical path method helps project managers know exactly when every activity must be completed and, by extension when resources are needed to complete them. As such, when resources come in, it is easier to know where their allocation should be prioritized at any given point in the project. More importantly, it is easy to know when resources can be redirected away from activities that can wait so they can be used to complete more pressing tasks.

5. Accurate Understanding of Project Status

First, readily available computer-generated charts within project management software help project managers identify a project’s critical path. Then, after project initiation, those same charts are used to assess in real-time whether the project is on time for completion, on schedule in the moment, and fully resourced. As such, reports are updated in real-time and downloadable at a moment’s notice for instant and clear reporting.

6. Scope Creep Management

As project managers go through the critical path, they can easily see if a given task along the path is taking more time or more resources than was originally allocated to it. As such, any deviation from the planned critical path alerts project managers that scope creep may be occurring, giving project managers the chance to change management plans before scope creep gets out of control.

7. Better Understanding of the Effect of Change Orders

Change orders happen on almost every project and can disrupt the entire project easily. Further, the cost and time required often must be altered. Critical Path programs can better integrate into the project the effect of change orders. 

Owner Understanding of Critical Path Method: 

For the owner of a project, often unversed in construction methods, it is perhaps easier to understand the role of critical path methods by comparing them to a day-to-day task. 

Consider cooking hamburgers on a barbeque for an afternoon gathering.  The cook will develop his or her own critical path, without calling it that. The cook will mentally identify all the activities within the project’s execution. Then, identify activity dependencies—or activities that must be completed one after another. Next, decide which ones are part of the critical path—or the longest sequence of dependent tasks. Also, decide which activities can be completed in parallel to critical path activities. Finally, map the project’s critical path and parallel activities.

When planning the barbecue, the general steps are as follows:

  • Ensure there is a grill, charcoal, lighter fluid, and appropriate weather or a place to be out of the rain. 

  • Purchase the meat and seasoning.

  • Light the grill.

  • Wait until the coals are hot enough.

  • Season the meat.

  • Time the arrival of the guests.

  • Determine from the guests how they like the meat cooked. 

  • Cook the meat. 

  • Serve the guests.

Identifying a Project’s Critical Path

Some of the tasks described above need to be completed one after another (sequentially) while other tasks are completed in parallel (concurrently). For example, the cook must wait until the coal is hot to cook the meat.  After a few minutes, the meat must be removed, or it will burn. The food must be served after the guests arrive but not so long that it is cold. Since none of these tasks should be initiated until the previous one has ended, they are dependent on one another.

Other tasks, however, can be completed in parallel to these dependent tasks. The cook can season the meat while the coals are heating. There is more flexibility regarding when to season the meat without delaying the completion of the entire project. This scheduling flexibility is called float time.

Tasks that do not have float time are part of the critical path. They must be completed one after another. They are also the longest string of dependent tasks in the project. Any delays in these activities will delay the completion of the entire project. Other strings of dependent tasks can float around them in that they can be scheduled when it is most convenient in the trajectory of the project.

For example, if you wait to heat the coals until after you season the meat, your entire project must stop until your coals become hot. For this reason, lighting the coals is part of the critical path. However, while you heat the coals, you can season the meat. These parallel dependent tasks are completed in addition to the critical path.

Critical Path Diagram

To demonstrate which activities are part of the critical path and which are not, project managers create a diagram. The diagram uses boxes to show which tasks are part of the critical path (have no float time) and which can be completed in parallel to those tasks (have flexibility in when they can be completed). 

The essential technique for using a critical path is to construct a model of the project that includes:

  • A list of all activities required to complete the project (typically categorized within a work breakdown structure).

  • The time (duration) that each activity will take to complete.

  • The dependencies between the activities.

  • Logical end points such as milestones or deliverable items.

Using these values, your critical path diagram will show the longest path of planned activities to logical endpoints or the end of the project, and the earliest and latest that each activity can start and finish without making the project longer. This process determines which activities are "critical" (i.e., on the longest path) and which have "total float" (i.e., can be delayed without making the project longer).

In project management, a critical path is the sequence of project network activities that adds up to the longest overall duration, regardless of whether that longest duration has float or not. This determines the shortest time possible to complete the project. "Total float" (unused time) can occur within the critical path. 

For example, if a project is testing a solar panel and task 'B' requires 'sunrise', a scheduling constraint on the testing activity could be that it would not start until the scheduled time for sunrise. This might insert dead time (total float) into the schedule of the activities on that path prior to sunrise due to needing to wait for this event. This path, with the constraint-generated total float, would actually make the path longer, with total float being part of the shortest possible duration for the overall project.

In other words, individual tasks on the critical path prior to the constraint might be able to be delayed without elongating the critical path; this is the total float of that task, but the time added to the project duration by the constraint is actually critical path drag, the amount by which the project's duration is extended by each critical path activity and constraint.

Crash duration

"Crash duration" is a term referring to the shortest possible time for which an activity can be scheduled. It can be achieved by shifting more resources towards the completion of that activity, resulting in decreased time spent and often a reduced quality of work, as the premium is set on speed. Crash duration is typically modeled as a linear relationship between cost and activity duration, but in many cases, a convex function or a step function is more applicable.

The Owner and the Critical Path:

As discussed in our article, “The Role of the Owner in the Construction Project-Doing More Than Writing Checks,” the sophisticated owner will participate in the construction project from initial planning to conclusion and not just hire someone and hope for the best. 

The wise owner will understand the critical path program dynamics and how change orders can drastically alter it. As one contractor client complained to us in an e-mail, “She keeps changing the project, generates change order after change order, but does not get that it’s like throwing a rock in a pool...ripples change everything...”

Nor will generalities solve the problem. Knowing that a change order or failure of a subcontractor to perform on time will delay the project does not tell you how much the delay will alter the timeline, how much it will alter the performance of others on the job site or the likely cost.  Knowing the basics of the critical path will provide much more information and the owner should have a grasp of it. You do not need to create your own critical path, but you and the contractor should review the one he or she created and discuss it as the job progresses. Since many contractors use computer software to develop the path, there is no reason that can not be shared and updated with the owner from time to time, and when change orders are made, integrated in. 

Many owners do not ask the proposed contractor to show the critical path analysis.  Many owners seem to think that this would be showing a lack of trust in the builder. However, demonstrating knowledge of this aspect of construction demonstrates that you are a knowledgeable owner and that is always good for the builder to know. And if the builder does not have such a program developed, that is a red flag for the owner.

For small projects some contractors do not need to use such a program and years of experience in such projects make it redundant. If one is having a small roof repair or installing one window, the experienced builder can rattle off the steps and path from memory.  But any major project, say costing over ten thousand dollars, should have at least a basic critical path program and the builder should not hesitate to show it to you. If he or she does object or says they do not have one, consider if this is the right builder for you.

One startup entrepreneur who operated with a team of a dozen employees commented that the critical path program was equivalent to the project management program he utilized for each project he undertook. The number of independent trades made it more complicated than a project involving only employees, but the variables - availability and delivery of materials, need for third parties to perform at the right time and changes in goals and extent of the project - were all similar. 

He further commented that participating in the development of the critical path program on the part of the owner makes the owner “part of the team.”  It means the owner knows ahead of time what a delay in delivery or a change order will cause. And that is invaluable.