The critical path is the longest chain of dependent activities through a project. Its length sets the shortest possible duration, and any delay to an activity on it pushes the completion date by the same amount.
Longest is the word that trips people up. It does not mean the most important work, the most expensive package or the activities with the highest risk. It means the sequence with no slack in it. A twelve million pound facade package may sit off the critical path while a two day survey sits on it.
Float is the amount an activity can slip without affecting something else. Total float measures delay tolerated before the completion date moves. Free float measures delay tolerated before the next activity is affected. Critical activities have zero total float by definition, which is what makes them critical.
In construction this distinction carries contractual weight. Extension of time claims generally turn on whether a delay affected the critical path, which is why the identification of that path at the time of an event matters as much as the calculation itself.
Take a simplified single storey extension. Excavate footings takes 5 days. Pour foundations, 3 days, cannot start until excavation finishes. Erect frame, 8 days, follows foundations. Roof, 6 days, follows frame. First fix electrical, 4 days, also follows frame. Plasterboard, 5 days, needs both roof and first fix complete.
After the frame the work splits into two parallel branches, then rejoins at plasterboard. The roof branch takes 6 days. The first fix branch takes 4. Plasterboard waits for the slower of the two, so the roof branch governs.
Critical path: excavate, foundations, frame, roof, plasterboard. Total 27 days. First fix electrical carries 2 days of total float, because it can start with the roof, take 4 days rather than 6, and still not delay plasterboard.
Now delay first fix by one day. Nothing happens to the completion date, because the float absorbs it. Delay it by three days and the branch becomes 7 days against the roof's 6. The critical path has moved, and it now runs through the electrical work. This is the behaviour that catches teams out: the critical path is not a fixed route through the project, it is a property of the current situation, and it can change without anyone announcing it.
Critical path calculation rests on assumptions that construction routinely violates. Knowing where they break is the difference between using the method and trusting it blindly.
None of this makes the method wrong. It makes it necessary but insufficient, which is why lean planning grew up alongside it rather than replacing it.
Practically, the critical path tells you where a delay hurts. Readiness tracking tells you whether the work will start at all. Used together they answer the question that actually matters on a Monday: which of the activities that cannot start this week is going to move the completion date?
Without the critical path, a blocked activity looks the same as any other and teams end up spending their attention evenly across problems of very different consequence. Without readiness, the critical path looks healthy right up to the morning the crew does not arrive. Most projects have one of these and not the other.
A useful habit is to review the lookahead with float visible against each activity. A blocked item with fifteen days of float is a task for someone this month. A blocked item with none is a decision for this afternoon.
That combination is what Playbook is built around. Dependencies and downstream impact are maintained alongside the readiness signals, approvals and confirmations that determine whether an activity can proceed, so the team can see not just that something is blocked but what it exposes and how urgently it needs a decision.
What is the critical path in construction?
The critical path is the longest sequence of dependent activities through a project. It determines the shortest possible project duration, and any delay to an activity on it delays the completion date by the same amount.
What is the difference between total float and free float?
Total float is how long an activity can be delayed before the project completion date moves. Free float is how long it can be delayed before the next activity is affected. Activities on the critical path have zero total float.
Can the critical path change during a project?
Yes, and it often does. When a delay consumes all the float on a parallel branch, that branch becomes the longest path and the critical path shifts to it. This is why the path should be reviewed at each schedule update rather than treated as fixed.
Why is the critical path not enough on its own?
Because critical path calculation assumes work begins as soon as its predecessors finish. It does not know whether materials, crews, approvals or access are in place, so an activity can be shown as ready to start while being impossible to perform.
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