What Float in CPM Schedules Means for Your Construction Project

By looking at float and criticality, a well-built CPM schedule paints the picture of what actually happens on-site.

Achieving optimal project efficiency hinges on fully understanding the concept of float in CPM schedules. As we dive deeper into its implications and how to utilize it, you’ll discover the critical role it plays in ensuring projects run smoothly from start to finish. 

 

What Is Float in CPM? 

 

Whichever scheduling software you use, the CPM algorithm does the math. It calculates start dates, finish dates, and total float (often called slack). To simplify, total float is the room for delay an activity can have before impacting the end date of the job. The second type, free float, indicates how long you can delay an activity without delaying the subsequent tasks. 

The Project Management Institute (PMI) notes that after calculating float, a series of critical activities appears. This sequence, known as the critical path, has the smallest amount of float and represents the project’s total duration. The term “critical” underscores the minimal slack in these activities– precisely, zero.

Float in CPM as an Indicator of Resource Priority

 

Differentiating between an activity with two months of float and one with zero is extremely important for managing resources. Obviously, everyone sees a red path surrounded by green and blue activities. However, many do not look at float as an indicator of how to prioritize resources. 

 

 

The critical path, highlighted in red, is your high-priority task list – where it’s most critical to prioritize your resources. Activities closely following this path, called the near-critical path, might vary in slack depending on the project’s size and complexity. Yet, any activity nearing 10-days of total slack is deemed “near-critical” by SmartPM standards. This, you should treat tasks with minimal slack (3-5 days) with the same sense of urgency as those on the critical path. 

For instance, given two tasks with identical start dates, the one with less slack should receive more resources to remain on track. In essence, resource allocation to the areas with the least slack ensures a smoother progression of the project. 

 

Determining Acceptable Values of Float in CPM

 

Determining sufficient values of float in CPM is a crucial aspect of project management. All project stakeholders can set these values by weighing the appropriate risk thresholds.

For linear projects, I recommend minimizing float and lengthening the critical path to ensure steady project progression. On the other hand, for both horizontal and vertical projects, it’s vital to maintain a reasonable amount for all parties. A strategy to achieve this is by integrating crew logic into the scheduling process, which ensures that labor constraints are taken into account.

The goal is often to have a month or less of float in CPM. Shorter float durations allow for clearer visibility into when and where impacts happen. Having a tight schedule, meaning one that thinks through all necessary logic, allows for clear identification of the critical path that drives the project. This kind of schedule control ensures any impacts to the schedule can be identified and addressed promptly.

 

Slacking Off on Slack

 

Float is only as useful as the schedule. This comes with the responsibility of ensuring your schedules are built with best practices. For example, if you have missing logic ties or a few bad practices built in, your critical path will be off, as will your slack values. 

So, number one, ensure you have high schedule quality. In fact, several DCMA schedule quality checks are associated with float, including missing logic, high-float activities, and average activity total float. 

 

Missing Logic

 

Every activity needs a predecessor or successor, except the very first and last. Ignoring this essential logic can result in skewed float values, altering the genuine critical path and rendering activity duration predictions unreliable. Furthermore, such gaps may conceal potential delays, impeding efficient analysis and informed decision-making.

 

High-Float Activities

 

A total float value of over 44 days presents a significant risk to a construction project. Excessive high-float activities (anything greater than two months) indicate flawed logic. As mentioned above, missing logic heightens the risks of hidden inefficiencies, delays, and an erroneous critical path. 

In any case, CPM schedules should have a minimal number of high-float activities. Ideally, schedules should be receptive to delays. Doing so allows project teams to gauge activity progression’s impact on the completion date.

 

Average Activity Total Float

 

Knowing the average amount of time your schedule’s activities have room for delay is helpful for two reasons. One, it informs you about the average permissible task delay without affecting the critical path. Secondly, if you have a high average, it could indicate an incomplete schedule. As mentioned above, incomplete schedules result in an erroneous critical path and the consequent challenges.

 

Staying Afloat with Float in CPM

 

Float in CPM isn’t just a project management metric; it’s a vital indicator for your project’s overall health. Apart from resource management, float offers: 

 

  • Flexibility and Contingency: Offers a buffer against unexpected challenges, ensuring activities can be postponed without jeopardizing the overall finish date.
  • Cash Flow Management: If certain activities have more than others and the others require more financing, then the extra amounts can be allocated accordingly. 
  • Decision Making: It can influence decisions on activity priority. For instance, if there are issues that might cause delays in multiple tasks, managers can use these values to decide which tasks should be prioritized to mitigate overall project delays. 
  • Stress Reduction: Instead of rushing to complete every activity, teams can work with a better understanding of which tasks have some leeway in terms of their completion dates. 
  • Stakeholder Communication: Slack provides a clear metric to communicate with stakeholders about potential delays and the flexibility present in the schedule. If a stakeholder is anxious about potential delays, understanding float can provide reassurance. 

 

By understanding the importance of float in CPM, you can not only create a buffer against uncertainties, you can also have more information to constructively influence your project outcome.

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