By Adam Zantis
For much of my career — as a planner, delay analyst and expert — the Critical Path Method (CPM) has been central to how construction programmes are developed, managed, and analysed.
CPM is powerful. It provides structure and transparency. It also aligns with how many construction contracts assess delay, typically focusing on whether an event delays the Date for Practical Completion.
That framing naturally focuses attention on the critical path.
However, after years working across both project delivery and disputes — and having researched the topic during my UNSW thesis, A Comparison of Critical Path and Critical Chain Scheduling, With a Particular Focus on Time Contingencies — I have come to believe that our industry’s reliance on critical-path-only thinking may sometimes narrow how we understand time risk on projects.
The distinction between Critical Path and Critical Chain approaches is often easier to understand visually.
In a traditional CPM network:
In a Critical Chain model:
This difference primarily changes how contingency is managed and monitored, rather than replacing CPM logic entirely.
Embedded contingency and behavioural effects
Traditional CPM schedules often contain contingency embedded within activity durations. This is a practical response to uncertainty and risk in project delivery.
However, the thesis research highlighted that distributing safety across individual activities can sometimes produce unintended behavioural outcomes, including:
When float or contingency is gradually consumed across several paths, the critical path may change late in the programme.
From a project control perspective, this means that risks developing on non-critical paths may not always be immediately visible, even though they may ultimately influence completion.
The thesis observed that the consumption of float and time contingencies frequently influences the eventual completion date, even where the effect is not immediately apparent.
Most construction contracts assess delay primarily by reference to the completion milestone. This provides a clear and objective basis for assessing entitlement.
However, in complex projects with multiple near-critical paths, events that affect non-critical paths can still influence project risk.
For example, events may:
These impacts may not always translate immediately into a movement of the completion date, but they can change the risk profile of the remaining programme.
Recognising and managing those risks early is beneficial for all parties involved in the project.
Critical Chain scheduling, developed from Eliyahu Goldratt’s Theory of Constraints, approaches contingency differently.
Rather than distributing safety within individual activities, it aggregates contingency into buffers that protect the completion date and key feeding paths.
Under this approach:
This framework focuses attention on system constraints and resource bottlenecks, which are often significant drivers of project performance.
The research concluded that Critical Chain techniques can provide greater visibility and control over contingency consumption, even though CPM provides more detailed control over individual activity durations .
Both approaches therefore offer useful perspectives.
The purpose of raising these ideas is not to suggest that CPM should be replaced. CPM remains an essential planning and analysis tool, and it is deeply embedded in construction practice and contract administration.
However, incorporating complementary concepts — such as explicit contingency management, buffer monitoring, or improved visibility of near-critical paths — may provide a broader understanding of programme risk.
This may assist project teams in identifying emerging risks earlier and responding proactively.
Modern construction projects are increasingly complex, resource-constrained and interface-heavy. In many cases, completion risk is influenced by a combination of factors rather than a single logical path.
CPM remains invaluable for understanding project logic and sequencing. Critical Chain thinking can help illuminate system constraints and contingency consumption.
Together, they highlight an important point:
Non-critical path delay is not necessarily unimportant delay.
Float represents valuable programme flexibility.
And resource constraints can influence outcomes long before the critical path visibly changes.
For project teams, developers and contractors alike, maintaining visibility of these broader dynamics can support better decision-making and ultimately improve project outcomes.
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