TIA vs. Windows Analysis

When a project slips and money is on the line, the delay methodology you choose shapes everything downstream: what the analysis costs, what it can prove, and how it holds up when someone qualified attacks it. Time Impact Analysis and Windows Analysis are the two workhorses, and they are often discussed as if they were interchangeable. They are not. They answer different questions, and picking the wrong one wastes money at best and hands the other side an argument at worst.

What a TIA actually does

A Time Impact Analysis models a specific event. You take the schedule that existed just before the event, the contemporaneous update, insert a fragnet representing the delay event and its logic, and measure how completion moves. It is prospective in nature: it asks what impact this event should have had on the plan as it stood at that moment.

That makes the TIA the tool of choice when the question is narrow and event-driven: a differing site condition, a design change, an owner hold, a late permit. It is also what most contracts explicitly require for time extension requests, which is reason enough to master it. A clean TIA is fast, contained, and persuasive because it uses the schedule both parties were already living with.

Its weakness is the flip side of its strength. Because it models what should have happened, a TIA can drift from what actually happened, especially if it is prepared long after the fact or stacked on other unresolved events. An opposing analyst's first move is to compare your modeled impact against the as-built record, and if the two diverge, your analysis reads like advocacy.

What a Windows analysis actually does

A Windows Analysis (contemporaneous period analysis) works through the project's actual history. You divide the job into windows, usually update to update, and in each window you measure what the critical path actually was, how much completion actually slipped, and what drove it. Then you assign responsibility window by window.

It is retrospective and observational: instead of modeling what an event should have done, it reads the record of what everything did. That makes it the strongest method when the dispute is broad, multiple delay sources, shifting critical paths, concurrency arguments, or a claim that spans most of the job. It is also inherently harder to attack, because it is anchored in the contemporaneous updates both parties exchanged every month.

The cost is real, though. A Windows analysis needs a usable set of updates and a serious time investment. If the update record is thin or the schedules were poorly maintained, you will spend much of the budget reconstructing before you can analyze.

How to choose

Start with the contract. If it prescribes a methodology for time extensions, that decision is made for you, at least during the project.

Then look at the question. One event, or a few discrete ones, with a live project and a decent current schedule: TIA. A finished or nearly finished project with delays tangled across its history, concurrency in play, or an all-in dispute heading toward mediation or litigation: Windows.

Then look at the record. The methodology is only as good as the schedules underneath it. Reliable monthly updates make a Windows analysis powerful. A stale or manipulated update record pushes you toward TIA plus a careful as-built reconstruction.

Timing matters most of all. The single best thing a project team can do for a future claim costs nothing: submit the TIA contemporaneously, when the event happens, not eighteen months later. Contemporaneous analyses carry a presumption of good faith that after-the-fact reconstructions have to earn.

The part nobody budgets for

Whichever method you choose, the analysis is only half the deliverable. The other half is making it legible: a chronology a principal can follow, graphics that show the critical path moving, and a narrative that connects cause to effect in plain language. I have watched technically sound analyses die in the room because nobody without P6 experience could follow them. The methodology wins the argument among experts; the communication wins it everywhere else.

Hartwell Consulting provides schedule and delay analysis, not legal advice. For entitlement and contract interpretation questions, involve your attorney, ideally before the analysis starts, not after.