McCullough and Associates

The Critical Path Method (CPM) of scheduling was developed in the 1950s as a way of managing plant maintenance projects for the DuPont and Rand Corporations. It is a method of determining minimum project completion time by analyzing interrelationships and approximate durations of all activities in order to determine the longest chain of dependant activities, the critical path.

For example, when building a house, there are various tasks like laying a foundation, framing, electrical rough-in, plumbing rough-in, sheet rock, painting, electrical finishing and flooring, to name a few. CPM looks at these tasks and sets a relationship, or “logic” between them. For example, the foundation must be finished before framing, rough electrical and rough plumbing can start. However all three of these activities must be finished before sheetrock can start. If we assign durations to these events, though, we’ll probably see that framing will take longer than electrical or plumbing rough-in. Therefore the framing is really the limiting activity for the sheetrock, and so the framing becomes a part of the critical path, along with the foundation and the sheetrock.

If activities on the critical path increase in duration, the duration of the entire project increases.

This is an incomplete and basic example. In actual construction projects, say for a multi-floor building, scheduling becomes much more complex and one must consider factors like contractor mobilization, manpower and material resources, and meeting contractual obligations and specifications.