Part 2 – Why do Construction Delays happen and How to analyse it

Construction_Engineering_43173Using Critical Path Method scheduling (CPM) provides analysts the needed tools to conduct a proper analysis. To understand the tremendous advantage of having CPM technology, please allow me to give you a brief idea about basic principles of CPM scheduling.

Prior to CPM scheduling, owners, contractors and any other businesses that needed schedules like large manufacturers used scheduling techniques where activities were listed and the sequence identified but the activities were not tied by logical relationships. Therefore, any delay or change of schedule needed reconstruction of the whole schedule. So, if we have a large schedule with hundreds of activities, you can imagine the cumbersome process of updating the schedule, say at 75% of the project or identifying the impact of a delay on the schedule.

The CPM method and the relevant software give the user the ability to tie the schedule’s activities by logic relationships. For example:

  • Activity B shall start when activity A is completed.
  • Activity C can start only when A and B are completed.
  • Activity D will start 5 days after activity A starts.

A scheduler builds a schedule by performing the following basic steps:

  • Define the activities.
  • Assign durations for each of the activities.
  • Identify the predecessor and successor activities.
  • Allocate the proper relationships similar to the described above.
  • The software automatically performs the CPM calculations, displays the schedule, gives you the completion date and identifies the critical and non-critical activities.

The CPM scheduling method helps the user do the following:

  • Update the schedule and clearly note the change of the completion date.
  • Manipulate the relationships and duration of activities to change the logic of the schedule to recover a delay and bring back the completion date to a desired date.
  • Insert a delay factor to an activity and immediately read the new completion date.
  • Identify the critical activities. These are the activities that don’t have any room (float) for any delays. A 3 days delay on a critical activity delays the whole project by 3 days unless the revised logic of the schedule dictates otherwise.
  • Identify non-critical activities. These activities have different amounts of float. A float of 20 days means that this activity can be delayed up to 20 days without impacting the whole schedule.

When the first submitted schedule is approved, it is considered a base schedule for future updates and delay analysis. That means the project manager needs to carefully review the schedule and the critical path prior to approving the schedule. Some of the elements that need careful review are:

  • Verify that the start and completion dates of the whole project match the contract dates.
  • Check that the assigned durations are realistic.
  • Review the logical ties between the activities.
  • Look through the critical path and check what activities are critical.
  • If the schedule show the phasing required.

Having introduced all these basic concepts related to delay analysis, please note below the different methods that are commonly used to analyze delays:

  • As-Planned vs. As-Built method
  • Impacted As-Planned method
  • Collapsed As-built or “But for” method
  • Window analysis method
  • As-Built method
  • Contemporaneous method

As-Planned vs. As-built method

The analyst compares the dates and durations of selected activities shown on the as-planned schedule with the actual dates and durations on an as-built schedule and considers the difference to be the delay on the job.

This is a very simplistic view of the delay claim because it ignores the following important factors:

  • The cause of the delays.
  • The timing of the individual delays and their impact on the schedule to be able to attribute the correct amount of delay days to the right responsible party.
  • It ignores the impact of concurrent delays.
  • It ignores the fact that the logic and sequence of the as-planned schedule may have changed through the project due to numerous delaying factors.

Impacted As- Planned method

In this method the analyst lists the excusable delays (or delays where time extension is owed to the contractor) and inserts the extended duration to the relevant activities. The analyst reads the revised completion date and calculated the days between this date and the as-planned completion date and determines that these are the number of days owed to the contractor. The sources of error in this method are:

  • It ignores the actual as-built schedule and events on site.
  • It assumes that the logic of the as-planned schedule reflect the reality on site.
  • It ignores the inexcusable delays that may have been concurrent to some of these inserted delays which impacts the number of days owed to the contractor.
  • Since the analyst is only using the as-planned schedule, this method doesn’t incorporate changes in logic and out of sequence work.

About Jamil Soucar

Jamil Soucar is a practicing and consulting general contractor, which includes expertise in Civil Engineering and has been in construction industry since 1983. He is a Certified Construction Manager by CMAA and holds a Certificate in Project Management from UCLA. His specialty is managing public works construction including schools, libraries, community centers and other commercial projects. His background includes private projects like singe family homes, restaurants and retail. He has done civil and structural design in the past, working on grading plans, surveys, subdivision maps, sewer, storm drain and street improvement. He has also prepared and taught several construction management training classes covering topics such as construction management, contract administration, change orders, logs, claims, principles of CPM scheduling, delay analysis and other relevant topics of interest to construction managers. Expert witness and article contributor for

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