Why the Critical Path Method (CPM) Is Not Lean
The Critical Path Method (CPM) has been widely taught and used in construction scheduling, but is it really the best approach? In this blog, we’ll explore why CPM is not lean, how it creates inefficiencies, and what you should consider instead.
What Is CPM?
If you’ve studied construction management, you’ve likely come across CPM. It’s a scheduling method where tasks are logic-tied, and an algorithm determines the longest sequence of dependent activities—the “critical path.” If any of these activities are delayed, the entire project is impacted.
On paper, it sounds reasonable. In practice, it’s a disaster.
The Flaws of CPM:
CPM is fundamentally flawed because:
- It compresses everything together – This increases work in progress (WIP) beyond the system’s capacity.
- It lacks buffers – The schedule is unrealistic from day one.
- It forces trade stacking – Overlapping work leads to inefficiencies and safety risks.
- It collapses under pressure – When delays happen (and they always do), logic ties dissolve, and teams scramble.
At the end of a project, CPM usually results in last-minute panic, overtime, and rushed work—none of which align with lean construction principles.
Why CPM Is Not Lean:
Lean construction is built on six key principles, and CPM fails in every category:
- Respect for People:
CPM disrespects teams by:
- Making schedules unreadable and unmanageable.
- Imposing unrealistic deadlines on trade partners.
- Forcing trades into unproductive, high-pressure situations.
- Stability:
A lean system is stable, predictable, and standardized. CPM creates chaos by:
- Pushing teams to work in multiple areas at once.
- Failing to provide a steady, reliable workflow.
- One Process Flow:
Lean emphasizes completing one process at a time before moving on. CPM disrupts this by:
- Forcing trades to start multiple tasks without finishing them.
- Ignoring trade flow and proper crew assignments.
- Flow:
Work should move in a predictable rhythm, but CPM:
- Ignores time-by-location planning.
- Fails to protect trade flow.
- Doesn’t allow teams to move efficiently from one zone to the next.
- Total Participation with Visual Systems:
Lean systems rely on visual tools that everyone can understand. CPM:
- Is a wall of text that no one can read.
- Creates schedules that even the scheduler struggles to follow.
- Excludes trade partners from effective planning.
- Continuous Improvement:
Lean thrives on feedback and refinement. CPM stifles improvement by:
- Hiding inefficiencies in complex logic ties.
- Relying on reactive measures like crashing schedules and working overtime.
The Bottom Line:
No matter how you analyze it—through lean principles, Theory of Constraints, or Toyota’s 14 Principles—CPM fails the test. It’s not a lean system. It’s outdated, inefficient, and needs to be replaced with better planning methods.
If you want to learn more we have:
-Takt Virtual Training: (Click here)
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-Listen to the Elevate Construction podcast: (Click here)
-Check out our training programs and certifications: (Click here)
-The Takt Book: (Click here)
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