What Is CPM in construction?
June 07, 2021
Looking for an effective scheduling method that can manage the vast number of tasks that make up your capital project plans? The critical path method (CPM), also known as critical path scheduling, is ideally suited for this as it is one of the most detail-oriented scheduling techniques. It’s expressed as paths of sequential activities with start and end points that represent the amount of time each activity takes. Once outlined, CPM shows the interconnection of all tasks — resembling a web or network — that are necessary to create the final build.
Why use CPM?
Reduce delays by focusing on completion of the most critical tasks along the path
It’s nearly impossible to focus individually on each of the thousands of activities that go into your project’s ultimate form and function. Instead, the critical path method enables you to identify the most critical tasks to manage along that path. These are the tasks that, when delayed or require more time to complete than scheduled, can throw off all dependent activities after them and jeopardize the project’s completion date. By ensuring proper allocation of time and resources, you can avoid potential delays. Plus, you can see which dependent tasks can be shortened to compensate for unavoidable time overruns.
Understand the true impact of how a schedule change affects other tasks
As tasks are completed, more precise task information becomes available, or when there is a delay, updating the CPM diagram will show the real-time impact on the associated dependent tasks and on the overall completion date. A new critical path may emerge from this, one that is different from the one you started with. That’s completely okay because this insight can help you better manage and plan remaining tasks accordingly going forward.
Assess and react to the impact of risks
With each task having an assigned duration, it’s easier to see the impact of delays because the critical path method automatically readjusts the schedule. So, if a particular task runs over by “A” number of days, it will show how the project completion date is then extended by “B” number of days. If this happens, you can visually determine where you can invest in extra resources or reassign existing ones to help make up for these delays.
How critical path method works
Determine the activities required to complete the project
It’s easiest to start with the main deliverables (reference your work breakdown structure). When you’re certain they’re accounted for, deconstruct them into smaller activities.
Sequence all activities
This part is especially important because the critical path relies on the accurate ordering of all tasks, creating a string of predecessor-successor relationships between them. That means some tasks absolutely cannot begin until another before it is finished; this is a dependency. And there will be other tasks that either can or should be completed simultaneously that won’t cause any negative impact on each other or affect their respective timelines.
Diagram out the network of all these activities
There was a time when this was mapped out by hand, but scheduling software can now do this for you. This diagram will lay out your activities in visual form, reflecting the order of all the project tasks based on the before-during-after dependencies you’ve incorporated.
Plot out the time each task will take
You can rely on the expertise of a skilled project manager to more accurately assess time estimates. Or, you could draw from similar past projects using the historical benchmarks you’ve collected. Precision is key here. The critical path method will only work if accurate time values are used. Otherwise you risk winding up with an unrealistic schedule that leads to costly delays. Worse, it could have consequences such as delayed retention payments or liquidated damages claims.
Despite how fine-tuned this scheduling method is, CPM does allow for some wiggle room through “float” calculation. This float value is the amount of time a task can be delayed before it affects dependent tasks or the project schedule as a whole. This is one of the strengths of this method.
The longest single sequence of tasks as shown in your diagram — determined by the durations you assigned to each one — is your critical path. This is how long it will take to complete your project.
Plan for resource allocation
This includes labor, space, materials and equipment. Parallel critical paths may show overlapping use of a particular piece of heavy equipment. Or multiple subcontractors due to work in the same area at the same time. This is because the critical path method assumes infinite resources. By introducing resource constraints, those resources won’t be scheduled simultaneously. But a more effective solution would be to call in some reinforcement from other software programs. Your options for other programs that can schedule resources include resource-oriented scheduling or Gantt charts, both of which allow you to essentially “rsvp” equipment for high-priority tasks.
CPM may seem complex process, but that’s exactly what makes it so appropriate for large-scale projects. Software can streamline your scheduling processes for you. InEight’s Schedule software is an advanced planning, scheduling and risk analysis solution that can help you track project timelines, workflows and progress using understandable visual formats. Request an InEight demo today.