Question

What activity and it's predecessors would be considered the critical path in the construction schedule of a two level 14, 000 seat Sports stadium?

Answer 1

The critical path method (CPM) is a staple of construction schedulers. Owners often require a critical path analysis. Construction management programs have taught CPM for decades, and courts use critical path schedules as evidence in construction disputes.

However, CPM intimidates many people because they find it complex and time consuming. Some construction superintendents and foremen view critical path as a theoretical abstraction that is irrelevant to their work. They believe that construction realities in the field should drive the schedule — with this approach, however, efficiency generally suffers.

Whichever construction scheduling approach you use, it’s clear that — after 60 years of increasing adoption — the critical path method is here to stay. Therefore, as a construction professional, you need to have a strong grasp of it

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How to Make Critical Path Work in Construction: From Theory to Field

by Diana Ramos on Nov 21, 2017

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The critical path method (CPM) is a staple of construction schedulers. Owners often require a critical path analysis. Construction management programs have taught CPM for decades, and courts use critical path schedules as evidence in construction disputes.

However, CPM intimidates many people because they find it complex and time consuming. Some construction superintendents and foremen view critical path as a theoretical abstraction that is irrelevant to their work. They believe that construction realities in the field should drive the schedule — with this approach, however, efficiency generally suffers.

Whichever construction scheduling approach you use, it’s clear that — after 60 years of increasing adoption — the critical path method is here to stay. Therefore, as a construction professional, you need to have a strong grasp of it. In this article, we offer a practical guide to making CPM work for your construction projects. You’ll learn basic techniques, get tips from experts, and find free downloadable templates.

In This Article

Understanding What Is Critical about the Critical Path Method

When working on any project, from cooking to construction, you know that a certain minimum amount of time is needed to complete the project. This minimum time spans a series of steps that follow a logical order. For example, when baking a cake, these steps are mixing the cake batter, baking the cake in the oven, letting it cool, and frosting it.

A step can only begin once all preceding steps have been completed. The total length of time needed to complete these steps is the length of time needed to complete the project.

To continue with the cake example, you might ask, “What about preheating the oven?” That step can be completed while you’re working on the other tasks, so it doesn’t add to the total project duration. And, it won’t necessarily lengthen the project if delayed.

The only steps that count towards project duration are those that contribute to the single longest series from start to end: mixing, baking, cooling, and frosting. In project management, we call this series of steps the critical path, and the constituent steps are the critical tasks.

The critical path method is a staple of project scheduling used across many industries where time is money. Construction stakeholders can use it to visualize and determine a project’s duration, and also use it as a shorthand for talking about how duration is affected when project variables change.

Construction project managers everywhere recognize a CPM chart since they have to study the method to obtain Project Management Professional (PMP) certification. In project-related disputes, the CPM is a legal standard for measuring project delays, and it is often used in court cases as the basis of financial claims.

The critical path method was developed in the 1950s by Morgan R. Walker at DuPont and James E. Kelley Jr. at Remington Rand. It was first used in a skyscraper construction project in the 1966 building of the World Trade Center’s Twin Towers. After a 1993 bombing, the team that oversaw repairs to the facility, who were working on a very tight schedule, turned to CPM to organize the work.

CPM was originally done by hand with paper and pencil. However, technology — starting with mainframes and proliferating with PCs — has made CPM much easier. Software applications use algorithms that schedule project activities and generate a graphic representation of project tasks and their relationships. We will discuss the role of software in greater detail.

Builders use CPM on major projects because the method is complex and demands a high level of expertise. They rarely use it for smaller construction jobs like building a house. Owners and contractors of commercial and industrial structures rely on critical path to create a baseline for on-time performance and document delays and, if the project is late, potentially act as evidence to determine fault and monetary damages.

These templates for construction documentation and inspection reports can help you verify your progress.

Download Construction Documentation Tracker Template

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‌ Download Daily/Weekly Inspection Report Template

CPM enables project managers to calculate the time and resources needed to complete a project. With good data, critical path can prevent scheduling problems and coordinate timely task performance by letting project managers know what needs to be done when. It allows supervisors to optimally schedule procurement and equipment usage and avoid overcrowding at the construction site. So-called stacking of trades, when too many specialty tradespeople are working simultaneously in a single area, hurts productivity and increases labor costs. So, good scheduling saves the project sponsors money in many ways.

Using the Critical Path Method with Other Scheduling Techniques

As CPM was emerging in the 1950s, the U.S. Navy and Booz Allen Hamilton developed a complementary scheduling technique called PERT (program analysis and review technique). Project managers use PERT to estimate durations for individual steps in a project and calculate completion time.

Today, the two techniques are used in tandem. CPM can also be used with a related technique called critical chain project management and with visual schedule trackers called Gantt charts. Let’s explore these tools.

PERT is essentially a probabilistic estimating technique for determining task durations. It was developed for U.S. Navy projects and implemented in the development of the Polaris nuclear submarine. PERT works using three duration estimates: the optimistic duration, the pessimistic duration, and the most likely duration. The optimistic duration is the shortest reasonable length of time necessary to complete the task, while the pessimistic duration is the longest reasonable length of time. The most likely duration falls somewhere in between.

PERT uses these three estimates to create a weighted average called the expected duration that tends to match actual task durations very closely. In this formula, the most likely duration is weighted more heavily than the optimistic and pessimistic durations. (You can find a handy calculator that will compute your expected value here.)

The outcome of a PERT analysis is called a PERT chart, an activity-on-arrow diagram that indicates expected task durations between project milestones. These expected durations can be plugged into a critical path model to identify the critical path and critical tasks. PERT is especially valuable to schedulers when tasks entail uncertainty and can be a helpful addition to CPM in those cases.

Another tool that schedulers use frequently with CPM is the Gantt chart, which was first used during WWI. The Gantt chart’s horizontal axis represents time, and bars represent project tasks. The Gantt chart represents activity relationships by showing how different bars line up with each other.