Negative Float, a Constraint, and a Time-Extension Request
A monthly update shows -22 days of total float on the MEP rough-in path, which per the schedule is not the critical path; the structural path shows 0 days of float and is labeled critical. Engineering and field use different calendars. A start-no-earlier-than constraint holds a vendor delivery to 1 September. A change order added 15 days of work to 'Exterior site utilities,' which has 40 days of total float. The contractor has requested a 22-day time extension, citing the MEP path.
1. Which path is actually driving project completion, and how would you verify it?
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Critical path is the longest path through the network to the completion milestone, not simply the path labeled critical in the software. The MEP path with -22 days of total float means it cannot finish by the required date given the constraint; that is a constraint violation and usually indicates the path is driving. The structural path's 0 days of float may be an artifact of a start-no-earlier-than constraint or of a different calendar. Verify by tracing the longest path in calendar days from the data date to the finish milestone, checking each path's duration, and reviewing all constraints and calendar assignments. If the -22 days is real and not caused by a constraint, the MEP path is driving. If the constraint is holding the vendor delivery, remove or justify it before drawing conclusions.
2. What is the effect of the 15-day change order?
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Exterior site utilities has 40 days of total float and the change adds 15 days, so it consumes float and leaves 25 days - no impact on project completion, and no basis for a time extension, provided the activity remains off the driving path and the added work does not change logic or calendar. Check two things: whether the added 15 days is sequential and actually consumes 15 days of float, and whether the change creates a new relationship or constraint that pulls the activity onto the critical path. If it does, re-run the analysis. Float consumption should still be reported as a trend even when completion is unaffected.
3. What analysis should support the time-extension request?
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Use a time impact analysis or fragnet inserted at the data date, showing the delay event on the driving path, with as-built logic and the before-and-after completion dates. Establish that the delay is on the longest path, is not concurrent with contractor-caused delay, and is not the result of a self-imposed constraint. Address the -22 days directly: if the MEP delay is caused by the contractor's own performance, the extension fails regardless of the path. Present the calendar normalization and the constraint review as part of the analysis. If an owner-caused event added 22 days to a path that was already late for contractor reasons, the compensable period may be less than 22 days.