2029-06-08
As-Built Finish
2029-03-07
But-For Finish
1. Methodology — AACE RP 29R-03 §3.7 (Modeled / Subtractive / Single Base)
Method
For each documented delay event, the as-built network is cloned, the event's
impact removed (by either shorten — reducing affected
activity durations — or remove — deleting the affected
activities and their TASKPRED edges), and the CPM forward pass re-run. The
resulting project finish is the "but-for [event]" date. The differential
between the as-built finish and the but-for finish is the event's attributed
impact under the Modeled / Subtractive method.
Citations
- AACE RP 29R-03 — Forensic Schedule Analysis Recommended
Practice, §3.7 Modeled/Subtractive/Single Base, §3.8 Multiple Base.
- SCL Delay & Disruption Protocol, 2nd ed., §11.5 — TIA
(forward) vs Collapsed As-Built (backward).
- Wickwire et al., Construction Scheduling, 4th ed., Ch. 10
— But-For analysis; dual-method convergence as evidence of method
reliability.
- Bramble & Callahan, Construction Delay Claims, 4th ed.,
§9.05 — Collapsed As-Built methodology; practitioner-consensus
dual-method convergence cut-offs.
Configuration
- Default removal method: shorten (per-event
override applies when an event specifies its own removal_method).
- Contractor filter: No — every event in the input list contributes to the cumulative pass.
Daubert input-uncertainty caveat: The subtractive method is
sensitive to the input impact_days values. A ±20%
input uncertainty on the per-event impact durations can swing the cumulative
result by a similar amount. AACE 29R-03 §3.7 recommends the analyst run a
schedule risk analysis (Monte Carlo with duration uncertainty distributions)
against the input durations and report the P50 ± P90 range alongside the
deterministic figures shown here. This dashboard reports a deterministic
point estimate; opposing counsel should be expected to attack the input
uncertainty on cross-examination — see the schedule-risk-analysis skill
output for the corresponding probabilistic envelope.
Concurrent-delay caveat: When two delays affect the project
simultaneously on overlapping paths, the subtractive method (this skill) and
windows analysis (forensic-delay-analysis MIP 3.7) can produce different
attribution. The cumulative pass treats all delays as additive; if the project
has concurrent owner-vs-contractor delays or two parallel critical chains, run
a concurrent-delay analysis (forensic-delay-analysis windows method, AACE
29R-03 §3.6) and reconcile against the output below. Dual-method gaps >10%
are a strong signal that concurrent delays are present.
2. Per-Event Subtractive Pass
For each delay event below, the as-built network was cloned, the
event's impact removed using the indicated method, and the CPM forward pass
re-run. The resulting "but-for" finish and computed impact are shown.
| Event ID | Name | Affected Activities |
Removal | As-Built Finish | But-For Finish |
Impact (d) | Responsible | Contractor? |
| E1 |
RFI #14 - Subgrade Contamination Spec Clarification |
A1020 |
shorten |
2029-06-08 |
2029-05-29 |
10d |
Owner |
N |
| E2 |
Subcontractor Crew Shortage - Subgrade Prep |
A1030 |
shorten |
2029-06-08 |
2029-06-04 |
4d |
Contractor |
Y |
| E3 |
Excavator Hydraulic Failure |
A2010 |
shorten |
2029-06-08 |
2029-05-31 |
8d |
Contractor |
Y |
| E4 |
PCO #07 - Mat Foundation Thickness Change |
A2020 |
shorten |
2029-06-08 |
2029-05-23 |
16d |
Owner |
N |
| E5 |
RFI #41 - Steel Weld Spec Clarification |
A3010 |
shorten |
2029-06-08 |
2029-05-30 |
9d |
Owner |
N |
| E6 |
Cladding Subcontractor Productivity Shortfall |
A4010 |
shorten |
2029-06-08 |
2029-05-25 |
14d |
Contractor |
Y |
| E7 |
Adverse Weather - TPO Membrane Install |
A4020 |
shorten |
2029-06-08 |
2029-06-01 |
7d |
Concurrent |
N |
| E8 |
CO-12 - Process Equipment Scope Addition |
A6010 |
shorten |
2029-06-08 |
2029-05-18 |
21d |
Owner |
N |
3. Cumulative Roll-Up
2029-06-08
As-Built Finish
2029-03-07
Cumulative But-For Finish
93d
Cumulative Impact (Subtractive)
Per-Event Impact Distribution
E1 — RFI #14 - Subgrade Contamination Spec Clarification
10d
E2 — Subcontractor Crew Shortage - Subgrade Prep
4d
E3 — Excavator Hydraulic Failure
8d
E4 — PCO #07 - Mat Foundation Thickness Change
16d
E5 — RFI #41 - Steel Weld Spec Clarification
9d
E6 — Cladding Subcontractor Productivity Shortfall
14d
E7 — Adverse Weather - TPO Membrane Install
7d
E8 — CO-12 - Process Equipment Scope Addition
21d
4. Dual-Method Gap
DUAL-METHOD VALIDATION NOT AVAILABLE
No forensic_result was supplied;
the dual-method cross-check between MIP 3.8 (Modeled / Subtractive / Single
Simulation — Collapsed As-Built / But-For, this report) and MIP 3.3
(Observational / Dynamic / Contemporaneous As-Is — Windows, from
forensic-delay-analysis) cannot be performed. To enable the cross-check,
supply forensic_result when calling
build_collapsed_as_built(). AACE RP 29R-03 §3.8
contemplates the cross-check on contested claims; tolerance bands applied
here (5%/15%) are forensic-engineering practitioner consensus per
Bramble & Callahan §9.05 and Wickwire et al. Ch. 10.