Time Impact Analysis (TIA)

Time Impact Analysis (TIA) is a delay analysis method where a specific delay event is modelled as an activity in a contemporaneous copy of the Accepted Programme, and the resulting impact on Completion (or a Key Date) is measured by re-running the schedule. It is one of the methods recommended by the Society of Construction Law (SCL) Delay and Disruption Protocol for assessing the time impact of a specific delay event, particularly when applied prospectively as part of a compensation event or variation assessment.

TIA is well-suited to contemporaneous delay assessment under NEC4 contracts, where compensation events require a defensible quantification of time impact at the point of assessment. The method: take the most recent Accepted Programme, insert the delay event as a logic-linked activity (or activities) with appropriate duration and logic, re-run the critical path, and measure the difference in planned Completion. Done properly, TIA produces an auditable impact quantification that links the specific event to the specific schedule consequence.

The method has limits. Retrospective TIA — applied after the delay has occurred — can be undermined by the as-built path differing from the as-planned critical path. Concurrent delays introduce complexity that TIA does not resolve automatically. And TIA is only as good as the Accepted Programme it operates on: a schedule with weak logic, excessive constraints or unreliable float will produce a TIA result that does not reflect the actual delay. For complex delay disputes, TIA is often combined with window analysis or collapsed as-built methods rather than used alone.