Class 106: Critical Path

What is a Critical Path?

The critical path is the “longest continuous chain of activities which establishes the minimum overall duration. A slippage or delay in completion of any activity by one time period will extend final completion correspondingly.”¹ Typically, the critical path has zero (or sometimes negative) float. The last activity on the critical path is often a contractual completion activity, called Substantial Completion.

What makes the critical path unique from other chains of activities in the schedule is that a delay to the start or finish of any one activity on the critical path will result in delay to the entire project by the same number of days. Essentially, the critical path determines the earliest possible completion date of the project and is used to calculate the overall project duration when using critical path method scheduling. If a construction schedule has multiple critical paths, the paths are called concurrent critical paths. Concurrency means “independent activities may be performed at the same time”¹, and in terms of the critical path, the concurrent activities are equally important to the project’s completion date.

Example of a Critical Path:

The example above shows a construction schedule for a high-end mixed-use skyscraper.  In the scheduling software, the red bars represent activities on the critical path and green bars identify activities not on the critical path. The green activities can become critical and turn red if they are delayed enough to have zero float. While all the activities shown, both red and green, need to be completed to finish the project, the critical path helps the project team concentrate on completing the activities that will surely delay the project if not completed on time.

1. The critical path is the sequence of activities that have zero or negative float and will therefore extend the overall project duration if delayed.

2. Identifying the critical path helps prioritize work, especially when resources are limited, to keep the project on track.

Critical Path – the longest continuous chain of activities which establishes the minimum overall duration

Float – amount of time an activity can be delayed without impacting the overall project

Activity – individual component or step of a construction schedule

Critical Path Method Scheduling – scheduling method that uses activity relationships and durations to calculate the earliest and latest start and finish dates for activities to determine the overall duration of the project

Concurrency – independent activities may be performed at the same time