The Role of Critical Path Method (CPM) in Construction Scheduling

Critical Path Method

When using resource scheduling and workforce management software, you have to complement the tool with proper resource and project management strategies. Among these strategies, the critical path method (CPM) is one of the most important ones designed for construction scheduling.

In essence, this method is ideal for the construction industry, ship construction, engineering design, and new product launch. For a project to be able to employ CPM, it must have a well-defined collection of activities constituting the end of the project when completed.

Plus, these activities must start and stop independently of each other in a proper sequence. There should be a continuous flow of activities. For example, in construction, a building’s foundation is constructed before roofing or wall erection. Let’s take a closer look at the role of the critical path method in construction scheduling.

If you’re looking for contractor scheduling apps, check out articles like the one written by Bridgit.

What is the critical path method (CPM)?

The critical path method (CPM) was developed in the 1950s to resolve the problem of inefficient scheduling and the increased costs resulting from it. Since then, the method has been employed in many industries to prioritize tasks and break down a longer project into smaller and more manageable parts.

In CPM, a network diagram visually represents the project tasks in a sequence. After defining the paths or task sequences, the duration of these tasks is calculated to find the critical path.

Previously, the critical path was calculated by hand. But now, most project managers use Gantt charts and software to automate and accelerate the process.

What is the critical path in a project?

The critical path is the longest sequence of tasks you must complete to complete a project. It’s called ‘critical’ because a delay in these tasks can lead to a delay in the whole project. Project managers must identify the critical path as it lets them:

  • Estimate the total project duration
  • Identify project risks and resource constraints
  • Create doable project schedules
  • Identify task dependencies and prioritize tasks

Why should you use the critical path method in construction scheduling?

Construction schedulers and managers should use CPM to get valuable insights on planning projects, scheduling tasks, and allocating resources. Here are some reasons to use this method.

Improves planning

With CPM, you can break a project into smaller tasks and plan your resources accordingly. The data from current projects can help project managers make informed decisions about future plans.

Enhances resource management

CPM helps project managers and schedulers understand how long tasks should take, how much they will cost in resources, and when to expect completion. Stakeholders can use this information to determine where and how to deploy resources.

Plus, it makes prioritizing tasks a breeze. For instance, a scheduler can easily identify which tasks are high priority and focus on those first.

Prevents bottlenecks

Bottlenecks lead to lost time. But when project managers use CPM, they can plot out project dependencies to identify which activities can run in parallel and which need individual attention.

How to use the critical path method (CPM) for construction project scheduling

Here are the steps to use CPM for construction project scheduling.

Step 1: List the activities

Start by listing all activities in the construction project with a work breakdown structure. The list will form the foundation of the project schedule.

Let’s say you’re constructing a home. Here are some tasks in the process:

  • Order materials
  • Lay the foundation
  • Erect walls
  • Install windows
  • Paint the walls
  • Lay flooring
  • Finish fixtures

Step 2: Identify dependencies

Now, determine which of these tasks depend on each other. It will help you see which tasks you need to do in parallel with others. For example, painting depends on the walls being erected and thus cannot happen before that.

Identifying dependencies is a crucial step so that you have an accurate timeline for the project.

Step 3: Create a network diagram

Structure the list of activities into a network diagram. It is a flowchart that shows activities in chronological order. Make a box for every task in the process and use arrows to show dependencies.

Step 4: Estimate durations

Estimate the duration of every activity in the list to find the critical path. You can make an educated guess using your knowledge or experience. If that’s not feasible, use the previous project’s data. If that’s not an option either, take industry standards from a reliable source.

You can also use the forward pass technique to calculate the critical path. In this technique, you calculate the early start and early finish dates.

ES (early start) is the highest EF (estimate finish) date of tasks that are a direct predecessor. EF is the sum of ES and project duration.

Start the calculation with 0 for the starting activity and continue with the succeeding tasks. The activities on the critical path will have the same ES and EF dates.

Step 5: Calculate float

Float is the flexibility you have for each task. It is the amount of time you can afford to delay a task without impacting any subsequent activity.

The float will tell you how flexible your project is. Your project must have a float to account for unexpected issues or risks arising during construction. The critical tasks in your project do not have a float as their dates are set. 

Non-critical tasks can have positive float numbers because you can delay them without affecting the completion date of the project.

There are two types of floats: total and free. Total float is the time you can delay an activity from the ES date without affecting the project completion date.

Free float is the time you can delay an activity from its ES without affecting any other activities. You can have a free float only when two or more activities have the same successor.


Now that you understand how Critical Path Method works, you can use it for construction scheduling. The key is to identify the activities that must be completed for the project to succeed and determine the best sequence of events.