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Scheduling

Float: what it is, who uses it and how to protect it

By Review.LivePublished 3 min readHow we write

The owner's representative replies to your latest schedule update: "Roofing shows fifteen days of float. That is our float, for our changes." An hour later the roofing subcontractor asks to start a week late, because "there's float anyway". Both are about to spend the same fifteen days.

A whiteboard divided into columns, with orange and blue sticky notes arranged in each one.
Photo: Paymo on Unsplash

Total float is how long an activity can be delayed without delaying completion; free float is how long it can be delayed without delaying the next activity. Total float is usually shared along a chain of activities, so when an early one uses some, the activities after it can be left with less. Who may use it is a contract question. Indiana's transportation department, for one, specifies that float belongs to the project and either party may use it until it runs out; a 2024 review of eleven US state transportation specifications found that most called float shared, three said nothing, and one required an activity for owner-owned float.

Reading and protecting float

  1. Read both numbers for each activity in the update: total float against completion, free float against the next activity.
  2. Trace the chain before anyone spends total float. Find which later activities share it, and whose work they are.
  3. Let trades flex within free float. A crew can shift inside its own free float without touching anyone else.
  4. Read the float clause and the time-extension clause together. Note whether float is shared, reserved or not mentioned, and whether a delay earns time only when it moves the completion date.
  5. Record every use of float in the update notes: the activity, the days used, the cause and who caused it.
  6. Keep durations honest. Padding durations to hide float makes the schedule a poorer forecast and gives everyone a reason to distrust it.

Action list

With this week's update

  1. Sort activities by total float and read the lowest ten
  2. Mark every activity with zero free float
  3. Find the float and time-extension clauses in your contract
  4. Log each use of float with the days, the cause and the party
  5. Tell the trades on any chain whose float drops below a week

Check your understanding

An activity has ten days of total float but no free float. Can it still hold up another trade tomorrow?

Show the answer
Yes. Total float is measured against completion, free float against the next activity. With no free float, any slip delays the successor's start at once, even though the finish date holds until the chain's ten days are gone.

Sources

  1. Project Management for Construction, Chapter 10: Fundamental Scheduling ProceduresCarnegie Mellon University · accessed
  2. Recurring Special Provision 108-C-215: Critical Path Method Schedule (5. Float and Scheduled Completion)Indiana Department of Transportation · Indiana, United States (one public owner's contract specification) · accessed
  3. A Comparison of Department of Transportation Progress Scheduling Specifications from Across the NationInstitute for Transportation, Iowa State University, for the Iowa DOT and the Federal Highway Administration · United States (specifications of eleven state transportation departments) · accessed

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