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Schedule And Delay Analysis Methodologies

By: Richard J. Long, P.E., P.Eng., Andrew Avalon, PE, PSP, Ronald J. Rider, MBA
Tel: (303) 972-2443
Email: Long International, Inc.

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The equitable allocation of responsibility for project delays is essential to the resolution of many construction disputes. Contractors frequently assert that they have been delayed for reasons beyond their control. Owners often remain unconvinced that the Contractor is legitimately entitled to a time extension or delay, acceleration and loss of productivity damages. Large dollar amounts may hinge upon the outcome of a dispute over project delay. Consequently, a thorough retrospective schedule analysis of all project delays is essential for the equitable resolution of delay and impact-related construction disputes.

Most construction contracts allow the Owner to recover either liquidated or actual damages for delay caused by the Contractor.  Contractors also may be contractually entitled to recover:

  1. extended  field  and  home  office  overhead  costs  because  of  Owner-caused  delays,
  2. acceleration and disruption costs if the Owner fails to approve valid time extension requests, and 3) loss of productivity costs if delays caused by changes in scope, events beyond the Contractor’s control, or the Owner’s interference disrupt and negatively impact the Contractor’s planned sequence and efficiency of performing its work. However, the Contractor’s actions as well as the actions of its subcontractors, vendors, and suppliers may also cause delay, disruption, and impact to the Contractor’s planned performance. Therefore, a retrospective schedule analysis must evaluate the contractual obligations and rights of each party.

The retrospective schedule analyses performed by Long International typically focus on comparing as-planned, updated and as-built project schedules to identify and quantify delays to the critical and near critical paths of the project. These delays may include either variances in the duration of an activity or variances in the planned and actual relationship lag durations between predecessor and successor activities. Concurrent delays are also analyzed to properly understand the Owner’s and Contractor’s liability for delay and impact damages. Once all critical and near critical path activity delays have been quantified, the origins and causes of each delay are determined. This process often involves the organization and analysis of extensive project documentation to establish the cause-effect relationships of each party’s actions or inactions and the resulting delays. The responsibility for each delay is then apportioned to either the Contractor, Owner, a third party, if appropriate, and to force majeure or other excusable delays defined by the contract.

Long International frequently performs “Update Impacted” and “As-Built But-For” schedule analyses using a windows approach to evaluate the contemporaneous, cumulative impact of delays caused by each party on the contractual completion dates. These two schedule analysis techniques determine the impact of delays during various schedule windows of time. The project schedule windows are typically based upon the data dates of the Contractor’s monthly schedule updates when the critical path may have changed due to key project events. The cumulative results of the analysis of delays to all schedule windows serve as the basis for an equitable apportionment of responsibility for delay and impact damages to the project participants.

In the sections that follow, Long International explains its detailed schedule analysis methodology using a construction delay claim on a hypothetical waste water treatment plant project. The fictitious parties in this example include the Owner, Olympia Chemical Corporation and the Contractor, Milestone Construction.

As shown in Figure 1, the Olympia Waste Water Treatment Plant (WWTP) project was planned to be completed in 502 calendar days. The actual duration, however, was 677 calendar days. Therefore, the net actual delay was 175 days. An update impacted and as-built but-for schedule analysis was performed to allocate responsibility for the 175 days of delay.

The update impacted analysis adds excusable delays into the schedule update to determine the cumulative impact of excusable delays to the project completion date. The update impacted analysis determines the amount of time extension that the Contractor is entitled to claim and the amount of liquidated damages that the owner is entitled to assess. For the Olympia WWTP project, the update impacted analysis determined that Milestone Construction is entitled to receive a time extension of 74 calendar days and Olympia Chemical Corporation is entitled to assess 101 calendar days of liquidated damages.

The as-built but-for analysis subtracts compensable delays from the as-built schedule for each schedule window to determine the earliest date that the Contractor could finish its work absent compensable delays. The cumulative amount of compensable delay calculated for all schedule windows using the as-built but-for analysis represents the total amount of delay for which the Contractor is entitled to recover extended field and home office overhead costs. For the Olympia WWTP project, the as-built but-for analysis determined that Milestone Construction is entitled to receive compensation for 27 calendar days of extended overhead costs.


Long International’s Update Impacted schedule analysis, as illustrated by Figure 2, adds excusable delays to affected activities in the Contractor’s schedule update at the start of each schedule window to determine how much time extension the Contractor is entitled to receive as a result of the excusable delays that occurred during the schedule window. Excusable delays may include compensable delays caused by the Owner such as change orders, late delivery of Owner- furnished equipment, or delayed approvals, or noncompensable delays such as strikes, unusually severe weather, or governmental actions for which the Contractor may also be contractually entitled to a time extension, depending on the contractual terms or case law.

For example, during each monthly update or schedule window, the Contractor may have experienced approved scope changes. New activities may have been added to the schedule updates to account for the new work associated with the approved changes, or the Contractor may have increased the duration of existing activities to show the effect of the increased work scope. The delays to each activity affected by the changed work are typically quantified by making estimates of the additional time required to perform the changed work or by including any time extension agreed in the approved change order into the critical path leading to project completion. A comparison of the actual activity durations and relationship lag durations that occurred in the as-built schedule at the end of the schedule window to the forecasted activity durations and relationship lag durations at the beginning of the schedule window may also be used to quantify the delay. However, Contractor-caused delays included in the activity durations or relationship lag durations of the as-built schedule updates are not included in the time extension calculation.

Changes that occurred during a schedule window may also affect existing activities beyond the data date of the schedule window. For example, if a change order is approved during the engineering phase that will add additional work to the construction of a piping system in a later schedule window, the increased duration is added to the affected future construction activity as part of the analysis of the earlier schedule window when the change was approved. By adding the excusable delays to affected schedule activities of the as-planned schedule as they occur, Long International determines the amount of time extension that would be required as a result of the delays. Acceleration paid for by the Owner may reduce activity durations or relationship lag durations and the Contractor’s entitlement to a time extension. As a result, the effect of any owner-paid acceleration is also evaluated in Long International’s schedule analysis.

The sum of the delay results that are calculated in each schedule window represents the overall time extension for the project. The projected extension in the schedule completion date compared to the contractually required completion date represents the amount of time extension that the Contractor is entitled to receive. For example, the update impacted analysis for the Olympia WWTP project determined that Milestone Construction is entitled to 1 calendar day of excusable delay in Window 1, 39 calendar days of excusable delay in Window 2, 27 calendar days of excusable delay in Window 3 and 7 calendar days of excusable delay in Window 4 for a total of 74 calendar days.

A comparison of the update impacted schedule completion dates to the as-built schedule actual completion dates, as shown by Figure 2, determines: 1) the amount of Contractor-caused delay in the as-built schedule that is subject to liquidated damages if the as-built completion date is later than the update impacted completion date, or 2) the amount of acceleration that the Contractor has accomplished if the as-built completion date is earlier than the update impacted completion date.


Long International’s As-Built But-For schedule analysis, as shown by Figure 3, determines the earliest date that the required project completion or Final Acceptance milestone(s) could be achieved if the compensable delays did not occur. Unlike analysis of delays to the critical path of the Contractor’s schedule update at the beginning of a schedule window, Long International’s As-Built But-For schedule analysis quantifies delay responsibility to activities on the actual critical path of the project that is calculated at the end of each schedule window. Because the actual critical path in each schedule window may be different than the planned critical path at the start of each schedule window, as illustrated by Figure 4, Long International’s As-Built But-For schedule analysis focuses on responsibility for delays that affected the dynamic nature of the actual critical path of the project. For example, at the beginning of Window 3 on the Olympia WWTP project, the as-planned critical path ran through piping procurement and installation. By the end of Window 3, however, fabrication and delivery delays caused the anaerobic pump installation to become the as-built critical path.

Long International quantifies the cumulative effect of compensable delays on the project completion date by first removing compensable delays caused by the Owner from the activity durations and relationship lag durations in the as-built calculation schedule1 for each schedule window and then recalculating the calculation schedule absent compensable delays. If the as-built calculation schedule completion date collapses to an earlier completion date after the Owner-caused compensable delays are removed, the net duration of the schedule collapse is the amount of compensable delay days for which the Owner may be liable for the Contractor’s extended field overhead and home office overhead costs. If the calculation schedule does not collapse, the Owner-caused delays that were removed were either: 1) not on the critical path, or 2) concurrent with Contractor-caused delays or other excusable but noncompensable delays that were also on the as-built critical path or parallel critical path(s) and prevented the completion date from collapsing to an earlier date. The net overall compensable delay at the end of the project is determined by adding the number of compensable delay days derived from the as-built but-for calculations in each schedule window. For example, the as-built but-for analysis for the Olympia WWTP project determined that Milestone Construction is entitled to 3 calendar days of compensable delay in Window 1, 20 calendar days of compensable delay in Window 2, 4 calendar days of compensable delay in Window 3, and zero calendar days of compensable delay in Window 4 for a total of 27 calendar days of compensable delay.


Long International’s detailed schedule analysis procedure includes the following steps:

  1. Identification of Schedule Windows
  2. Correction of the Schedules and Verification of Actual Dates
  3. Development of a Reasonable As-Planned Schedule for the Start of Each Schedule Window
  4. Development of As-Built Calculation Schedules for Each Schedule Window
  5. Preparation of Duration and Lag Variance Tables
  6. Identification of Delays and Allocation of Delay Responsibility
  7. Schedule Calculations to Determine Delay Liability

A more-detailed discussion of each of these steps is explained in the following sections.


For both the Update Impacted and the As-Built But-For schedule analyses, Long International analyzes delays to the Contractor’s work during specific schedule “windows” of time. This windows approach enables Long International to assess the dynamic as-built critical path throughout the project as the Contractor’s work was performed and affected by delays. Although performed retrospectively, the analyses evaluate the effect of delays as they occurred and cumulatively over the entire period of the project. Typically, Long International starts with the Contractor’s original planned schedule and schedule updates to establish the as-planned and as- built schedules during each schedule window. Using either each monthly schedule update or combining several consecutive updates to define a schedule window, Long International establishes the specific window periods for its analysis based on the data dates of the schedule updates and the timing of key events during the project that may have caused changes to the critical path.


Based on its review of the Contractor’s schedules, Long International identifies any deficiencies or errors that, if not corrected, would substantially affect the accuracy of the delay analysis results. For example, the Contractor’s schedule updates may contain inaccurate or inconsistent actual dates. Long International validates the actual dates in the Contractor’s schedules against dates recorded in contemporaneous project documentation such as engineering drawing logs, purchase orders, material receiving reports, daily construction reports, test reports, punch lists, meeting minutes and monthly progress reports in order to verify the accuracy of the schedule activity actual dates. This step ensures that the as-built schedules accurately reflect the actual start and finish dates for completed work activities and properly forecast the critical path for the remaining work scope.

Common schedule deficiencies that Long International examines and corrects include the following:

  1. Incorrect and inconsistent use of as-built dates;
  2. Activity planned durations that are inconsistent with the Contractor’s bid estimate calculations;
  3. Missing contractual scope of work;
  4. Lack of contractually required completion activities;
  5. Over use of constraint dates;
  6. Missing predecessor or successor logic ties creating open-end activities;
  7. Inadequate   depiction    of    equipment    and    materials procurement and delivery activities;
  8. Inaccurate predecessor logic for Owner approval activities;
  9. Lack of a contractual Owner approval period for submittal and turnover packages;
  10. Lack of reasonable project punch list and demobilization periods;
  11. Inconsistent use of Calendars, Progress Override and Retained Logic schedule calculation options; and
  12. Unrealistic as-built logic relationships indicating out-of-sequence progress.

After the above schedule deficiencies or errors are corrected, the Contractor’s as-planned and/or as-built critical path may be different than the Contractor or Owner thought during the project. Therefore, conclusions regarding the effect of and responsibility for delays may be different if the schedule deficiencies or errors were not corrected.


To perform the update impacted schedule analysis, Long International first ensures that the schedule updates at the start of each schedule window are reasonable, i.e., the schedule deficiencies identified above have been corrected. Long International then uses the scheduling software to recalculate the corrected schedules to determine: 1) the reasonable baseline schedule at the start of the project prior to any scope changes or delays, and 2) reasonable schedule updates that not only identify consistent and accurate as-built dates for activities that have started and finished prior to the schedule data date but also correctly forecast the planned start and finish dates of remaining schedule activities at the start of each successive schedule window. These schedule updates represent the as-planned schedules for the start of each successive schedule window. Figure 5 graphically depicts the forecast critical path at the start of Window No. 3 of the Olympia WWTP project schedule analysis. In this example, the critical path to achieving Final Acceptance by November 7, 2002 is being driven by the delivery of piping materials.

Liquidated damages may apply to not only the project completion date but also to intermediate milestone activities. Using the reasonable as-planned schedule at the start of the project and the forecast schedule updates for the start of each successive schedule window, Long International sorts and organizes the activity data by float value and/or longest path to identify the driving paths for each contractually required milestone date and the overall critical path leading to the project completion date.


To perform the as-built but-for schedule analysis, Long International prepares an as-built calculation schedule for each schedule window. The as-built schedule window can be defined as the period of time between the data dates of two or more successive schedule updates. The as-planned schedule update with its data date at the beginning of the schedule window contains forecast start and finish dates during the schedule window period. The as-built schedule update with its data date at the end of the schedule window contains actual start and finish dates during the schedule window period.

Forecast start and finish dates and float values in a CPM schedule are driven by the schedule logic and the original or remaining durations of the schedule activities. When actual dates are used to update a schedule for work that has started and/or finished during the as-built schedule window, the actual dates override the schedule logic to fix the as-built dates of the activities. Therefore, there is no float assigned to activities having actual finish dates in a statused schedule. Therefore, the as-built critical path cannot be readily identified with only the statused schedule containing fixed, as-built dates.

The as-built calculation schedule converts the fixed as-built schedule dates into calculated early start and early finish dates based on actual activity durations and as-built logic. The as-built calculation schedule forecast dates are the same as the as-built schedule dates but are calculated by the scheduling software using as-built schedule logic and actual activity durations instead of using the fixed actual dates input to the schedule. For example, as shown in Table 1, the as-built calculation schedule forecast dates are the same as the as-built schedule actual dates for Window No. 3. This process enables Long to determine the actual float values and actual critical and near critical paths during the as-built period of the schedule. Identification of delays to the as-built critical path is vital to determine the actual causes of the delay to the project...

Download PDF to continue reading article, footnotes, figures, tables, and references.

Long International provides expert claims analysis, dispute resolution, and project management services to the Process Plant Engineering and Construction industry worldwide. Our primary focus is on petroleum refining, petrochemical, chemical, oil and gas production, mining/mineral processing, power, cogeneration, and other process plant and industrial projects. We also have extensive experience in hospital, commercial and industrial building, pipeline, wastewater, highway and transit, heavy civil, microchip manufacturing, and airport projects.

Richard J. Long, P.E., is Founder and CEO of Long International, Inc. Mr. Long has over 40 years of U.S. and international engineering, construction, and management consulting experience involving construction contract disputes analysis and resolution, arbitration and litigation support and expert testimony, project management, engineering and construction management, cost and schedule control, and process engineering. As an internationally recognized expert in the analysis and resolution of complex construction disputes for over 30 years, Mr. Long has served as the lead expert on over 300 projects having claims ranging in size from US $100,000 to over US $2 billion. He has presented and published numerous articles on the subjects of claims analysis, entitlement issues, CPM schedule and damages analyses, and claims prevention. Mr. Long earned a B.S. in Chemical Engineering from the University of Pittsburgh in 1970 and an M.S. in Chemical and Petroleum Refining Engineering from the Colorado School of Mines in 1974.

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