Compression in Construction Project Scheduling: Ten Best Practices

The Nature of Implementing Recovery Measures in CPM Construction Project Scheduling

It is the exception that a large and long construction project finishes on time without some sort of mitigation or recovery effort being mandated by the client.  Schedulers are tasked with representing how prospective mitigation and recovery efforts may reduce negative-float, and bring a project back into the contract window. The representation will only be as accurate as the schedule baseline logic, otherwise, the mitigation or recovery sequences won’t make sense.

The terms compression and acceleration are manifested similarly in Construction Project Scheduling– augmentation of forces, otherwise the distinction is not visible to the naked eye. But they have different connotations. In both, the rate of production is increased to finish sooner than a projected finish date. Acceleration is typically the moving up of a contract finish date, as requested by the owner. A contractor may ask for compensation from the owner to bankroll the cost of acceleration.

Compression refers to stepping up production in order to recover negative float. As a preventive measure against negative float creep, a scheduler may be asked to introduce mitigation strategies into the schedule to stave off expected slip. These strategies may include compression. Once mitigation efforts don’t pan out and the end-date slips, the scheduler generates a compressed recovery schedule for approval.  A contractor may ask for compensation from the owner to bankroll the cost of the compression necessary to realize the recaptured float, but the distinction: delay or disruption must first be determined.

In order to make up for lost time a contractor may be compelled to augment his forces and man-power either with more resources over existing forces, more shifts, or both. He may expedite or “red-label” critical path deliveries. He will require his sub-contractors to sign up for the recovery plan. The augmentation of forces is a general contractor’s or construction manager’s knee-jerk reaction to jump-starting a delayed or disrupted project. It is not always a scientific practice. Engaging more resources without being able to quantify the effects of a compression plan limits the ability to effectively control the plan.

Used properly, CPM scheduling software is a scientific practice for compression. A scheduler can model different recovery scenarios (in P6 I create a Reflection schedule) and perform analytics to determine the optimal recovery project logic. More sophisticated schedulers also rely on risk assessments (RA) and other risk management software – such as Monte Carlo models, to optimize recovery for more complicated projects. Alternatively, smaller and less complex projects don’t need a complicated RA to put together their recovery plan.

CPM schedules are the most efficient tools of accountability available that general contractors can use for representing delay claims to their clients. Indeed, in the US Court systems CPM schedules take precedence over any other schedule reporting medium – a spreadsheet, for example. For that reason, best practice dictates that recovery efforts are designed and monitored with a CPM schedule, which can readily output accurate data pertaining to project logic – information that can later be used to substantiate a claim. Naturally, the claim schedule will be examined for veracity and therefore must clearly illustrate each delayed float-path.

The later in the project the recovery takes place the less time there will be to react and recover. Not uncommonly, a critical point is reached late in the project, where a contractor will opt to “bomb” a job, or inundate the site with as many workers as possible. The purpose of a recovery schedule is to obviate the need for bombing the job. Some of the downsides of bombing a job are:

  1. Increased likelihood of mistakes
  2. It is an unscientific method subject to the laws of chance
  3. Trade and manpower congestion
  4. Increased shift-work leads to more accidents
  5. Pressure on the design team to keep up with the works
  6. Subject to upcharges for increased manpower

A project may be disrupted by the owner: his actions or inactions hold up the builder, or delayed by the builder: his forces are not prosecuting the work on schedule, due to his own miscalculations or performance. This is a critical distinction where liability is at issue. If the contractor is the cause of a delay, he will issue a recovery schedule, and absorb any upcharge or expenses to facilitate the recovery effort. If a disruption is cause by the owner, and there are upcharges associated with facilitating recovery, it will be incumbent upon the contractor to demonstrate how to the owner.

Delay claims are notoriously seldom honored or awarded by owners, or the courts, as contractors’ schedulers never seem to be able to unequivocally demonstrate the cause and effect of a given delay. It is the bailiwick of the scheduler to generate a claim schedule. The delays will only be represented by the scheduler as accurately as the quality of information received from the contractor, and the integrity of the project baseline logic.

Ten Best Practices of Compression

  1. Most importantly, generate sequences and project logic that include SS lags, and tight free-float values in your baseline, not later in the recovery schedule: a baseline schedule should be optimized before the recovery schedule. You don’t want to find that your baseline durations and sequences were too liberal, or that they included excessive free-float.
  2. Put on your contractor’s hat, and try to visualize your compression plan in action. If you are a scheduler with limited field experience, such a visualization may seem pretty elusive, which is why I have always said the best raw scheduling material comes from schedulers with field experience. If you do have field experience, you will be less reliant on outside information to build your recovery plan. In other words, suppose that eight-months in, a two-year project was projected to be two-months late. The contractor requires that the scheduler balance the schedule (zero float). If the scheduler can simply change some relationships from finish-to-start to start-to-start + lag, and make up the negative float without compression, it will be plainly evident that the baseline was not optimized.
  3. Just as you would during the baseline process, always coordinate compression efforts with the respective contractors, and confirm that they buy in.
  4. Enact compression from a practical standpoint: if a trade is not delayed, they may not need to enhance their presence on the site, lest they end up standing against the wall to stay out of the way, while they wait for other work to finish.
  5. Optimize your baseline such that there are no inordinate float values.
  6. Carefully document the changes you made. P6 Claimdigger can do this in a tabular report, but there is no operability within the output. There are others scheduling programs and analytic/forensic software that do a much better job – Acumen Fuse, for example.
  7. Calendars: be aware that if shifts are added to facilitate compression, you may have to generate a separate calendar for some of your new or existing activities, or modify your resources. I have had mixed usability results using multiple schedules in Primavera 6, and would recommend people check P6 forums and Oracle knowledge-base for more information on what I am referring to.
  8. Remember that there are long-lead items and fabrication windows on various schedules that also must be massaged by the scheduler. For example, if a concrete deck is not poured by the time an equipment plant is ready to be shipped, the equipment will likely have to go into storage either with the fabricator, or elsewhere.
  9. Maintain the integrity of your schedule and updates. Schedules typically deprecate in quality as the project progresses, making recovery efforts difficult.
  10. Read my recent post on why it’s so difficult for contractors to collect on disruption claims.



Written by

Derek Graham is a Primavera 6 scheduler and schedule oversight consultant for public and private sector projects with four decades of construction industry experience. He has been an active construction expert witness in over 30 cases - both nationwide, and Federally, since 2006, when his book Managing Residential Construction Projects, was published by McGraw Hill