DELAY ANALYSIS TECHNIQUES-AS BUILT BUT-FOR AND TIME -IMPACT METHOD

The third method I am going to describe is called as-build but- for and time-impact analysis. This is a more sophisticated method. In brief, as built but- for involves removing the effects of delay events from the as built programme in order to assess how the work would have progressed in absence of the delays.

First a dynamic as built programme is produced using planning software to create a model of the timing and sequence of actual events. The model must precisely replicate how the works were executed using as built start dates, finish dates and activity durations with appropriate activity logic links between activities. 

The second stage involves identifying the delay events in the as built progrsmme and apportioning them to the the party responsible for them.  The delay events are shown in the as built programme either as activities or constraints. Their impact is modeled by creating logic events between the delay events and subsequent activities.

The third stage involves removing the delays from the as built  programme to produce an as built- but programme to show how the works would have been constructed but for the delays. When used in claims for extension of time, only delays for which the contractor is not responsible are removed. It can be argued then that the extension of time due is the difference between respective completion dates of the as built programme and as built-but for the programme. In practice several iterations are needed to ensure that the model represents what would have happened but for the delays. This involves adjusting the level of detail, logic and durations of activities. 

As this method relies upon having an accurate as built programme, good as built records are essential. It is vital that the construction team is consulted in order to gain an  understanding of  the methods of construction, relationships between  activities and practical impact of delays.

This approach has a number of advantages. It is fact based and less theoretical than other methods. The basic principle is easily understood and it can be easily presented and explained. It does, however, come with a warning:care is needed to ensure that the model addresses the concurrent culpable delays, re-sequencing, redistribution of resources and acceleration. If such matters are not accounted for then the final results will be misleading.