What are the main retrospective delay analysis methods?
Retrospective delay analysis looks back at a finished or stalled job to find what delayed it. The main methods are as planned versus as built, impacted as planned, collapsed as built, time impact analysis and windows analysis.
The methods in short
- As planned vs as built: compare the original programme with what happened. Simple, but it does not show cause.
- Impacted as planned: add the delay events to the baseline programme. Quick, but it ignores what the contractor really did.
- Collapsed as built: remove the delay events from the as built programme to show when the job would have finished. Good for a clear event.
- Time impact analysis: add each event to the programme as it stood at that time. Fair, but it needs good programme updates.
- Windows analysis: split the job into periods and study the critical path in each. Strong for long jobs.
How to choose
The best method depends on your records. A job with monthly programme updates suits time impact or windows analysis. A job with only a baseline and photos may only support a simpler method.
The contract can also set the method. Some require the programme at the time of the event. Read the clause first.
Why it matters
The method changes the answer. Two analysts with the same facts can reach different days. State your method, your records and your assumptions so the other side can follow the work.
Related answers
Questions
Which method is the most accepted?
Methods that use contemporaneous programmes and test each period, such as windows analysis, are often seen as stronger. The records on your job decide what is possible.
Is there a standard guide?
Yes. The Society of Construction Law Delay and Disruption Protocol and AACE guidance describe these methods.
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