Understanding Critical Path Method in Construction

The Critical Path Method is a popular method that construction project managers use to schedule out big projects. But it isn’t always a well-understood method of scheduling for others in construction. It can look and feel somewhat arbitrary or like it doesn’t effectively estimate and build schedules. But that’s not the case, when used correctly the Critical Path Method can be an incredibly useful scheduling tool that will improve overall efficiency.

What is The Critical Path Method (CPM)

The Critical Path Method or Critical Path Analysis is a way of setting schedules for a set of projects or activities. The Critical Path Method or CPM was developed in the late 1950s and usage of it has increased in the decades since it’s creation. It’s commonly used in construction, but it’s used in other industries as well. It’s typically used on larger projects rather than smaller projects because it’s less efficient overall to create these plans for shorter or smaller projects. CPM can make superintendents and project managers uncomfortable because it isn’t always clear or easy. However, to become PMP certified, they must learn this.

Using CPM

As CPM developed so did PERT. PERT or Program Analysis and Review Technique is typically used in conjunction with CPM. PERT is an estimating technique used to determine task length. It looks at

Optimistic Duration, this is the shortest reasonable length of time to complete a task

Pessimistic Duration, this is the longest amount of time needed to complete a task

Most Likely Duration, this is the most likely about of time required to complete a task

It uses these durations to calculate the expected duration, which if done correctly is highly accurate. These calculations must be set per task and are then fed into a Critical Path Model to identify the critical path and critical tasks. From there a scheduler, project manager, or superintendent can schedule out a project.

What’s Needed in CPM

CPM is constructing a model of the project. Therefore, project managers and superintendents need to have a few essential information points.

1. List of Activities. They need to have a list of all activities required to complete the project. Managers typically will use a work-breakdown structure to be able to list all of the activities and when they need to be completed.
   1. The Work-Breakdown Structure is a breakdown of a project into smaller components. These smaller components are organized by hierarchy, or what needs to be completed first.
2. Time. The project managers or superintendents must have the duration of each activity. This is important in determining the overall schedule. While using PERT, they should be able to get a reasonably accurate estimate for the total length of each part.
3. Dependencies. Project managers or superintendents must consider the various dependencies between activities. In construction, there are specific tasks that MUST happen before other tasks because it would be impossible to start them without it. These are dependencies and need to be considered when planning the project.
4. Milestones and Deliverables. In order to know when a task or activity is complete, the project manager must know when the project should end and what the end looks like. Also, many subcontractors are paid based on their deliverables so knowing what the deliverable would look like is essential for many factors.

With all of these in mind and the tips to using CPM and PERT, it should be easier to understand what goes into CPM scheduling and visuals.

Visualizing CPM

There are a couple of different ways to envision the critical path method. Some people use the activity-on-arrow visual, or critical path diagram, which breaks each activity into a box with the amount of time totaled at the top and lines directing viewers to the next step of the project. Sometimes there might be multiple lines to indicate multiple next steps. However, the more common method of visualizing CPM is the Gantt Chart. A Gantt Chart can act like a critical path schedule and show the dependencies between different activities and many scheduling platforms can display the status of a given project. This can help manage a project because the superintendent can see which activities are falling behind or which activities might fall behind.

Integrated Labor Delivery and Critical Path Method

The way the Critical Path Method is used now it only looks at an overview of each project from the side of a General Contractor or Construction Manager. However, when subcontractors and trade contractors look at the schedule they have to take it and recreate their schedule with all of their own dependencies. Subcontractors and trade contractors are experts in their field and they know what the timeline for their specific piece of work will be. When construction managers and general contractors bring in subcontractors into the process they can get a better more detailed schedule and they are able to improve the accuracy of their scheduling.