What Is Float in a Construction Programme?
Float is how long an activity can slip without consequence: total float before the project end moves, free float before the next activity moves.
The two kinds
Total float = latest start − earliest start: what the activity can absorb without delaying the project. Free float: what it can absorb without delaying the earliest start of the activity immediately after it. Critical activities have zero total float.
Its management value
Float is a resource to be managed: it drives the order of priorities and the levelling of resources — delay what has float in favour of what is critical. In disputes the question “who owns the float?”, the employer or the contractor, inevitably arises, so it is best settled in the contract.
How it erodes
The network is recalculated at every progress update: activities that looked comfortable can lose their float and become critical. Watching float periodically is an early warning worth no less than watching the critical path itself.
Worked example
An aluminium installation activity has an earliest start in week 12 and a latest start in week 15: three weeks of total float. A two-week delay in delivery consumes the float harmlessly; the third week puts it on the critical path, and the fourth delays handover.
FAQ
Is free float always smaller than total float?
Free float never exceeds total float, though it may equal it — because it is the tighter constraint: not disturbing the next activity, rather than only not disturbing the project end.
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