Quick answer: Time Impact Analysis fits projects with a sound baseline and discrete, documentable delay events; Windows Analysis fits complex projects with multiple concurrent delays and a complete series of contemporaneous updates; Collapsed As-Built fits completed projects where a reliable periodic update record was never maintained.
Three Methods, One Decision
Time Impact Analysis (TIA), Windows Analysis, and Collapsed As-Built are three of the forensic delay methodologies most frequently used on construction delay claims. Each has already been compared head-to-head elsewhere on this site — see TIA vs. as-built: choosing a delay method and windows analysis vs. collapsed as-built for the two-way breakdowns. This guide puts all three side by side, because the real-world decision is rarely a straight choice between two options — it is an assessment of which single method, among several, actually fits the record a specific project produced.
Side-by-Side Comparison
| Factor | Time Impact Analysis (TIA) | Windows Analysis | Collapsed As-Built |
|---|---|---|---|
| How it works | Inserts a specific delay event into the accepted baseline (or latest update) at the point in time it occurred, and measures the push to the completion date. | Divides the project timeline into discrete windows, usually bounded by schedule updates, and analyzes how the critical path changed within each window. | Starts from the as-built schedule and removes specific delay events one at a time to show what completion would have been without them. |
| Records required | A well-developed baseline schedule with honest logic and float, and discrete, documentable delay events. | A complete, logically sound series of contemporaneous CPM updates covering the disputed period. | A detailed as-built schedule (often reconstructed from daily reports, RFIs, submittals, and correspondence) and a documented basis for each delay event removed. |
| Best suited for | Contracts where the specification requires TIA, and where delay events can be analyzed close to when they occurred. | Complex projects with multiple, possibly concurrent, delays from more than one party. | Completed projects where contemporaneous updates are missing, inconsistent, or were never maintained. |
| Strengths | Most widely specified and accepted by public agencies; analyzes delay close to the time it occurred. | Most rigorous for isolating concurrent delay and assigning responsibility between parties; anchored to documents that existed before the dispute. | Usable even when no reliable update history exists; works from what actually happened rather than a theoretical projection. |
| Weaknesses | Loses credibility if the baseline was poorly built or float was artificially constrained. | Time- and record-intensive; not usable without a reasonably complete update series. | More vulnerable to challenge because it depends on assumptions about what would have happened absent the delay, developed after the fact. |
How to Choose Among the Three
- Check the contract's scheduling specification first. If TIA is specified, use TIA — deviating from a specified method invites an immediate challenge regardless of the analysis quality.
- Inventory the schedule update history. A complete, logically sound series of contemporaneous updates supports Windows Analysis. A thin or inconsistent update history pushes the choice toward Collapsed As-Built or, where only the original baseline survives, Impacted As-Planned.
- Assess whether delays are discrete or concurrent. A small number of clearly separable delay events fits TIA well. Multiple delays from different parties overlapping in time are better isolated through Windows Analysis.
- Confirm the project status. An active project with ongoing updates supports TIA or Windows Analysis performed in near-real time. A completed project being analyzed after the fact, with no usable update series, is the typical Collapsed As-Built scenario.
- Apply the method consistently. Switching methods mid-analysis because a different one produces a more favorable number is one of the fastest ways to lose credibility with a reviewer or opposing expert.
The Underlying Requirement Is the Same
Regardless of which of the three methods applies, the common requirement is a schedule and field-record history thorough enough to support the analysis honestly. Methodology selection optimizes what is possible with the record a project actually produced — it cannot substitute for a record that was never created. That is the case for building and maintaining schedules defensibly from the baseline forward, discussed further in forensic delay analysis and extension of time claims.