Showing how a change moved the finish date
The owner's representative issues a change on a two-storey car dealership: a second electrical room for future vehicle chargers. The electrical subcontractor says the switchgear shop drawings must be redrawn and re-reviewed before ordering. You think the finish has moved; she wants to see it in the schedule.
For a change not yet carried out, copy the last accepted update from before it, add its activities tied to the work they affect, recalculate with nothing else altered, and compare the forecast finishes: the difference is the modelled effect. An owner can check that insertion against its accepted schedule. A UK industry protocol calls this a time impact analysis, and the US Army Corps of Engineers' guide specification requires the last approved schedule before the impact, with no other changes unless approved; it may require an interim update if that schedule is too old.
- Copy the last accepted update from before the change, and note its data date, finish and critical path. Not the baseline, unless no update exists yet, and not an unaccepted re-plan.
- Build the fragnet: the change's own activities — revised drawings, resubmittal and review, delivery, installation, inspection — each with a duration, a responsible party and its basis.
- Tie it in with every predecessor and successor, as the work would run.
- Recalculate and compare the forecast finishes. If the fragnet only uses float, completion does not move.
- Check the result with the superintendent: the new driving path should make sense on site. Wrong logic found elsewhere is fixed only by agreement, and shown separately.
- Put it on one page — change, fragnet, both finishes, float used, critical path before and after — and send it while the change is being priced.
Common mistakes
- Quietly fixing other activities in the same run.
- Claiming the whole fragnet as delay, despite the float.
- Waiting until the job ends, when nobody agrees what the schedule showed.
Checklist
Before you send the analysis
- Last accepted update before the change
- Fragnet durations, parties and basis
- Fragnet tied in at both ends
- Nothing else changed in the copy
- Both forecast finishes and the float used
- Notice sent separately
Check your understanding
The owner's scheduler asks why you used last month's update, not the baseline, where the switchgear chain had 20 days of float. What do you say?
