Methods of delay analysis

There are various delay analysis techniques commonly used within the construction industry. Prospective methods are used in live projects to forecast the impact of events upon the date for completion using critical path analysis. The methods used are:

  • As-planned impacted
  • Time-Impact analysis

Retrospective methods are used to deal with time extensions after completion of the project. There are five main techniques.

Most delay analysis techniques have their critics and all should be used in the knowledge of their weaknesses and limitations as well as their strengths. So, what are the techniques and what are the main strengths and weaknesses of each?

As-planned v As-built

This method is simple and quick to prepare, does not require a networked programme, relies upon actual progress and is widely recognised. Perhaps importantly, it is the cheapest and simplest method of analysis.

However, the method does require an as-built programme and accurate as-built records. There is also a subjective assessment of critical paths as it does not identify critical paths and to that extent depends upon the opinion or “experience” of the expert.

As-planned impacted

This method is quick and simple to carry out and understand, transparent and an As-built programme is not required.

Ignoring what actually happened on site is a major flaw and the method is often seen as a technique of last resort.

Collapsed As-built

This method is easy to understand, inexpensive once an As-built has been produced and relies upon actual progress. An As-planned programme is not required.

Its main weaknesses are that as-built start and finish dates for delay events are required and there is a subjective assessment of as-built logic.

Time-impact analysis/snapshot

This method is the method required by NEC/EEC forms as it functions as both a prospective and retrospective method. It is simple to understand and relies upon actual progress as the As-built status is tracked through the project.

However, the method is both time consuming and costly when performed forensically. It requires a reasonable and robust as-planned logic linked programme. It can be difficult if there are many delay events and it cannot be used if progress records are not available. There is a risk of theoretical conclusions and it can suffer from the “black box syndrome” on large complex projects.

Windows/time slice analysis

This method is a variant of the time-slice method and is particularly effective at dealing with a large number of events. In short, it looks at delays on a real-time basis and by splitting the project into shorter periods, it makes it easier to analyse the events. It also enables different methodologies to be used in each window so the analysis is relevant to activity. The downsides to this method are that it can be time consuming and costly to prepare, detailed as-built information is needed, the planned programme simply reflects what was intended and does not take the history of project into account and it does not impact events individually, only collectively.

Which method should be used?

There is probably no right answer to such a question because different methods require different data. The method used will largely be dictated by a number of factors.

In the second part of this article in the next edition of Building Blocks I shall cover what the courts look for in terms of delay analysis and make suggestions as to how to win in court.