In project scheduling, the precision of our plans dictates the success of our execution. However, the lag element is often misused and misunderstood. Excessive dependence on lags can affect schedule clarity, complicate updates, and create disputes.
Let’s explore why it’s important to minimize lags and when to replace them with task-dependent activities to enhance schedule integrity.
Why Are Lags Problematic?
Lags are time delays applied between activities to represent waiting periods or preparatory work. For example, a planner might add a 7-day lag between two Activities to represent “work preparation.” While this approach seems convenient, it introduces several challenges:
- Lack of Attributes: Unlike activities, lags do not carry attributes such as descriptions, durations, or percent complete. This makes them untrackable and excludes them from scope definition or progress monitoring.
- Ambiguity: The meaning of a lag might be clear to the schedule developer but not to reviewers, project stakeholders, or future users. This can result in disputes and misleading forecasts.
- Impact on Claims: In cases like Extension of Time (EOT) claims or delay analyses, lags can lead to conflicting interpretations. For instance, is a 7-day lag representing site clearance by the client or work preparation by the contractor? Such ambiguity can delay resolutions and escalate disputes.
To avoid this conflict, the contractor can make the purpose of each lag clear in the baseline narrative report but it is not a common or practical approach.
Lags Best Practices
Wherever possible, lags should be replaced by task-dependent activities. For example, instead of inserting a lag for “work preparation”, introduce a task-dependent activity called “Work Preparation” that has its own attributes like a clear description, duration and relationships.
This approach provides several benefits:
- Clarity and Accountability: Activities are fully trackable.
- Transparency: Reviewers and stakeholders can clearly understand the project scope.
- Reduced Disputes: Activities eliminate the ambiguity of lags, reducing the potential for conflicting interpretations.
While replacing lags with activities is often ideal, lags have their role in specific situations. For example, a Start-to-Start (SS) + lag relationship between “Block Work” and “Plaster Work” is convenient. This is acceptable when no intermediate tasks occur during the lag period.
Consequences of Misusing Lags
Lags are frequently used by planning engineers for:
- Material Handling and Storing: Delays in moving or storing materials.
- Work Preparation: Time needed to organize resources before starting a task.
- Curing: Waiting periods for concrete to set.
While these scenarios are common, introducing an activity often provides a better solution, offering greater control and clarity. Moreover, excessive lags can result in significant challenges:
- Void in Scope Definition: Untraceable lags create gaps in the schedule that cannot be monitored.
- Misleading Forecasts: Ambiguity in lag interpretation can impact project timelines.
- Complicated Dispute Resolutions: In delay claims, conflicting interpretations of lag meaning can lead to costly and time-consuming disagreements.
Conclusion
Lags must be used strategically in project scheduling because overuse or misuse of lags compromises the schedule’s clarity and reliability. By replacing critical lags with task-dependent activities and minimizing unnecessary lags, we can create robust schedules that are both reliable and easy to maintain in the future.
Regards,
Osama Saad, MBA, PMP, PSP, CCP, PMI-SP
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