Schedule Change Management
A change order adjusts the price — but a change only shows its true effect on time once it's modelled into the CPM as real activities and logic. Build the fragnet, recompute the critical path, and read the delay. Built on AACE 109R-19.
Why schedule change is its own discipline
Cost and time are not the same currency. A $60,000 change might add zero days (it ran in parallel, on float) — while a $5,000 change might add three weeks (it sat squarely on the critical path). You cannot read time impact off the price; you have to model it.
Does the change move the finish date?
Every schedule change falls into one of two buckets, and the difference is everything.
| Non-critical change | Critical change | |
|---|---|---|
| Where it sits | On an activity with spare total float | On (or pushing a path onto) the critical path |
| Effect on finish | None — float absorbs it | Every day of change is a day of project delay |
| Extension of time? | Not due | Due — this is where EOT entitlement arises |
| Prolongation cost? | No | Yes — extended site overhead for the added days |
The fragnet — modelling the change in logic
Instead of guessing "this adds about two weeks," you build the change as real activities — with durations and relationships — and the CPM does the arithmetic: it recalculates early/late dates and tells you exactly how many days the completion moves.
Worked example — reading the time impact
The same three-activity chain, before and after the fragnet. The project baseline finish is day 45 (10 + 15 + 20).
Baseline vs. impacted critical path
Worked example| Path | Logic | Duration | Finish (day) |
|---|---|---|---|
| Baseline critical path | A→B→C | 10+15+20 | 45 |
| With fragnet CO-1 (8d) | A→B→CO-1→C | 10+15+8+20 | 53 |
Those 8 critical days entitle the contractor not just to the direct cost of the rock removal (priced as a change order) but potentially to 8 days of extended overhead. At, say, $3,200/day of extended site overhead, that's an extra 8 × 3,200 = 25,600 over and above the direct work.
Prolongation calculator
Set the critical delay the fragnet adds and your extended site-overhead rate. See the prolongation cost — the time-related claim that rides alongside the direct change.
Critical delay & prolongation
Try it yourselfSet the critical delay the fragnet adds and your extended site-overhead rate to see the prolongation cost — the time-related claim alongside the direct change.
The update discipline — keeping the model honest
Fragnets are only trustworthy if the schedule they're inserted into is itself current. That requires a steady update rhythm: progress actuals recorded each period, logic changes documented with reasons, and a clear line between as-built history (what happened) and the forecast (what's planned from the data date forward). Insert a change into a well-maintained, regularly-statused schedule and the time impact is credible. Bolt it onto a stale or manipulated schedule and the analysis collapses under scrutiny.
Ten things to remember
- You can't read time impact off cost — a change's effect on the finish must be modelled.
- A change is non-critical (absorbed by float) or critical (delays the project).
- The tool is the fragnet — real activities and logic, not a guess.
- Insert the fragnet, then recalculate the critical path — it often moves.
- Consuming float can create a new critical path.
- Only critical delay earns an extension of time.
- A critical change has two recoveries — direct cost and prolongation.
- Keep direct and time-related costs separate and clearly derived.
- Fragnets are only credible inside a regularly updated schedule.
- Never hide impact by quietly altering downstream logic — document every change with a reason.
Glossary
- As-built schedule
- The record of what actually happened — actual start/finish of completed work.
- Critical path
- The longest chain of dependent activities; any delay to it delays the project.
- Data date
- The "as-of" line in a schedule update: actuals to the left, forecast to the right.
- Extension of time
- Additional contract time granted for an excusable critical delay.
- Fragnet
- A fragmentary network of activities and logic representing a change, inserted into the live schedule.
- Prolongation cost
- Time-related cost of extending the project — extended site overhead, supervision, facilities.
- Schedule update
- The periodic statusing of progress and logic that keeps the CPM model current.
- Total float
- The time an activity can slip without delaying the finish. Zero float = critical.