Project Monitoring with Window Analysis
By: Kamyar Beihagi, PMP

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Introduction
Over the years, Critical Path Method (CPM) scheduling has become the most commonly utilized construction network scheduling method. However, when a project delay occurs, the parties must be able to depend on the schedules to show what was delayed and for how long. Networking techniques have great utility in evaluating delay and impact on a project. Among the most widely accepted CPM schedule delay analysis techniques used today is the Windows Analysis method. This approach looks at consecutive time frames of the project, known as Windows, and quantifies the delays or gains based upon the critical and near critical activities. Although the Window Analysis method is frequently performed towards or at the project’s end, this technique can also prove beneficial if performed on a regular monthly basis during the project’s execution with the use of the updated monthly schedules. Most contractors use the Time Impact Analysis (TIA) method to forecast an owner caused or extra work delay and then use the analysis for time extension negotiations. The TIA method is beneficial in forecasting delay; however the Window Analysis is beneficial in understanding exactly what delayed the project during a specific time period. As such, performing the Windows Delay Analysis on a regular monthly basis is beneficial in documenting “what happened” on the project. This paper will explain and highlight the fundamental steps necessary to perform an accurate and defendable Windows Analysis and will explain the many advantages of using such analysis during project execution to monitor the project’s progress.

CPM Scheduling Methods
In today's construction industry, the planning, scheduling, execution, and monitoring of project activities are generally represented by graphical network schedules known as Critical Path Method (CPM) schedules. CPM scheduling was developed in the late 1950s to assist in the building and maintenance of chemical plants at DuPont. These schedules identify the activities that must be performed, the planned sequence, and the planned duration of the activities to complete the work by an agreed date (i.e. contract completion dates). These schedules are used to monitor the project progress by measuring the actual work completed against the work planned, also known as the baseline schedule. CPM scheduling employs certain terms to describe different scheduling concepts. Some of these terms include: activities, durations, logics, early start, early finish, late finish, late start, criti­cal and near critical activities paths, and floats.

CPM schedules analyze what activities have the least amount of scheduling flexibility (i.e., are the most critical) and then can predict project durations based on the activities that fall on the critical path. Activities that are on the critical path of the network cannot be delayed without delaying the completion of the entire project. Projects planned with this CPM technique typically are represented graphically in a diagram showing how each activity is related to the other activities. (Figure 1) The project is structured so tasks are dependant on each other so that critical tasks and their paths can be identified as follows:

• Early Start - Starting from the earliest starting task in the project, the early start of the task is the early start of the dependent preceding task plus the previous activity's duration. This is calculated for all the task activities.
• Late Start - Starting with the last task in the project, the latest starting time of the preceding activity is the latest starting time of the task minus its duration. This is calculated for all the task activities.
• The difference between these two numbers is the activity’s float.
• The path to the project completion compromising of the dependent activities with the least amount of float establishes the project’s critical path.

The critical activities and the critical path to completion, by definition, cannot be delayed or take longer than their estimate without impacting the time of the overall project, as they contain no float (or slack). Other tasks in the project can be delayed or take longer without affecting the duration of the project, provided that their float does not fall below the critical float values.

Figure 1- Simple Example of a project’s critical and near critical paths

The Importance of Project Schedule Monitoring
With the ever increasing project costs and the time being of the essence in most of them, the monitoring of a project’s schedule is of significant importance. Project monitoring can reveal potential problems and can be used to consider corrective actions to mitigate delays and / or extra costs. To increase the project’s success in finishing on time and / or on budget, developing a schedule is necessary but not sufficient: it is mandatory to monitor the project progress, to detect any issue and to accompany the needed changes. Without knowing the current status of the project and to foresee any upcoming issues, the project has a significantly higher rate of being delayed. At the onset of a project, a baseline schedule is created. During the progress of a project, the contractor updates its monthly schedules and submits them to the owner. The delays are usually depicted in the slippage of the project critical path float from the previous month. However, to understand exactly what happened during the previous month, the parties need to look back and perform a schedule analysis. The analysis should reveal the delays, if any, which occurred during the previous month or a longer period of time. The overall goal of a project schedule is to give the project participants a reasonable management tool, which enables them to effectively and economically plan and execute construction projects, while still maintaining the flexibility to effectively and promptly react to the dynamic nature of construction projects. Using the CPM scheduling method to monitor the project critical path allows contractors and owners to detect which activities have caused any delays. In addition, an accurate, consistently used and updated CPM schedule allows both parties to determine how and when the project completion date was impacted. Most of today’s ever more complex construction projects encounter events and / or changed conditions that affect the original plan for their execution. As such, proper planning and scheduling can minimize the risk of a delay and in the case of disputes a correct delay analysis can assist in determining “who is going to pay.”

Types of Delay
Project delays are those that cause the project completion date to be delayed. Disruption is an interruption in the planned work sequence or flow of work. Disruption is distinguished from delay in that the duration of work activities or the overall project comple­tion may not be extended, but the sequence of the planned work might change. All delays on construction projects can be classified into three groups:

• Excusable, compensable - these delays are caused by the fault or shortcoming of the owner. The contractor is entitled to both an extension of time and an increase in the contract price to compensate for additional costs.
• Excusable, non-compensable - these delays are those for which neither the owner nor the contractor are responsible. Earthquake and heavy rains are some examples. Excusable delay is caused by factors beyond the control and without the fault of either the project owner or the contractor. The contractor is entitled to an extension of time, but not an increase in the contract price.
• Non-excusable - These delays are caused by the fault or performance deficiency of the contractor, for which he is liable to pay damages to the owner. The contractor is entitled to neither an extension of the schedule nor an increase in the contract price.

These three delay types can occur in separate time periods or in parallel, also referred to as concurrent delay. Concurrent delay is experienced on a construction project when two separate delaying events occur during the same time period. The concept of concurrent delay is one of the most contested topics in the construction industry. Both owners and contractors use concurrent delay as an excuse to avoid the responsibility for claims of extended overhead or liquidated damages assessments. Other classification of delays refers to dependencies between delay types. These include:

• Independent delays - delays occurring in isolation of one another and not as a result of a previous delay.
• Serial delays - delays arising as a result of an earlier delay, also known as ripple impacts and dependent delays.
• Pacing delays - Pacing delay is explained by deceleration of the project work by one of the parties due to a delay caused by the other party, so as to maintain steady progress with the revised project schedule. Pacing delays, in their true form, will not delay the project completion dates.

Schedule Delay Analysis Methods
There are many types of schedule delay analysis methods with various methodologies. Some of the more commonly used methods include:

• As-Built Analysis - This analysis can be successfully used in cases when the contemporaneous schedules do not represent the true project condition (i.e., updates were not made; the schedules were flawed or somewhat manipulated). The As‑Built Analysis presents a simple comparison between what was the plan and what the actual. Although simple and widely used, the As‑Built Analysis method cannot capture the project’s dynamic and changing environment and does not represent the critical path in real time due to the fact that the as‑built schedule was developed "after the fact."
• As-Plan Impacted Analysis - This analysis compares the completion date of the originally planned baseline schedule with the impacted baseline schedule. This method does not give adequate results because the inserted impacts in the plan schedule are quite subjective (do not require verification with the actual duration) and do not consider any acceleration or delays during the progress of the work.
• Time Impact Analysis - Contract specifications relative to scheduling have become more specific in their requirements for controlling and monitoring project execution and also in specifying what type of analysis shall be used in case of a project delay. The most widely recommended type of delay forecasting technique, and the one used most often to request a time extension, is the Time Impact Analysis (TIA) method. This analysis is required by many governmental schedule contract clauses such as the Veterans Administration and the U.S. Army Corps of Engineers. TIA is the recommended analysis for projection of an extension to the project completion date due to additional work, owner‑caused delays. Normally, the contract includes a detailed procedure for time impact application and also specifies that the contractor shall prepare and submit schedule fragnets (a fragnet is a collection of activities that represent a portion of the project) within a specific time frame to demonstrate the influence of delays or to support requests for any time extension. To apply TIA, the project must be divided in different time periods. Each period starts when there is an impact to the project's critical path. For each time period, the delayed or impacted activities shall be analyzed separately and the cause of the delay shall be considered. Whether the delay was caused by the contractor or the owner, the fragnet representing the impact shall be added to the project network. After all impacts are added, the difference between the planned completion date and the completion date after the impact occurs represent the project delay. Not all impacts occur on the critical path; some can be on concurrent paths with lower float values and will not necessarily affect the project completion. Therefore while evaluating impacts, the float values shall be considered and only impacts affecting the critical or near critical path shall be measured. Although used frequently, it is impossible to apply TIA on projects with multiple overlapping changes or delays with long durations because of all the assumptions that have to be made regarding remaining durations for the activities being impacted. The TIA method does not give an accurate representation of the expected project completion if the anticipated performance is not realistic; in other words, the contractor should make a very accurate projection of the duration of the impact. Another downside of TIA is that many times the contractor does not link the impact with the correct activities in the planned logic and therefore there is no true representation of the impact. Another disadvantage of this analysis is that during the impact period of an event, another non-considered and perhaps a contractor caused delay can overtake the project delays and make the initial time extension granted due to an owner caused delay an inaccurate projection.
• Windows Analysis - One of the most widely recognized methods for contemporaneous delay quantification is the Window Analysis method. Window Analysis is accepted by legal authorities around the world. This methodology has been in use for over 20 years and is widely recognized as the most effective and reliable methodology to identify critical delays on large, complex projects. The Window Analysis method focuses on the critical path delays that occur during specific periods of time called "windows" and uses the contemporaneous project schedules to establish what the "real time" critical path of the project is at any point in time through the project. The window period is defined by the calendar period between major changes to the schedule critical path or any contract changes, such as a time extension. That critical path may and typically does change over the course of the project. Thus, each formal update of the schedule during the course of the project is reviewed to determine whether the critical path changed and if so, how and when the critical path changed. At each change in the critical path, a new window time period is identified. However, before a valid critical path can be identified, it is necessary to review and analyze each schedule to determine whether the schedules were reasonable relative to whether the work shown on the schedule could in fact have been accomplished as planned for the window period in question. When electronic schedules are available, the underlying assumptions upon which each of the schedule activity durations and logic ties were based can be reviewed and analyzed in order to validate those underlying assumptions. This process thus serves to determine whether the schedule itself was reasonable, a basic premise upon which Window Analysis methodology is based. If the assumptions were reasonable, then the schedule can be analyzed as it was used to manage the project and can be utilized as the basis for delay identification, duration, calculations, critical and near critical paths, etc. However, if the contemporaneous project schedules are based on faulty assumptions (i.e., applying numerous unnecessary and non‑contractual constraint dates or including activities that are sequenced incorrectly), then the contemporaneous project schedule has to either be discarded or it must be "adjusted" to show the proper underlying assumptions. Because each window represents a segment of time, the delays quantified for each window must be summarized at the end to determine the total project delay. The activity delay quantification is then followed by the root cause analysis determining the underlying factors and identifying the party or parties responsible for any delays.

Difference Between Windows Analysis and Time Impact Analysis
Both Time Impact Analysis and Windows Analysis use the contemporaneous schedules to demonstrate the impact of a delay to the project critical path. However, there are distinctive differences between these two delay analysis methods. TIA is a useful technique for forecasting the impact of a delay to the project completion date. However, many assumptions are incorporated into the analysis that might later prove wrong. For example, the contractor needs to correctly estimate the duration of the extra work activities, lead times, and the necessary relationships to other activities within the network. These decisions usually become points of disagreements between the parties, which might cause further impacts until the parties can agree on the underlying assumptions. Windows Delay analysis is beneficial in “looking back” and in determining exactly what occurred. The assumptions are taken out of the process and the true delays are highlighted. Windows Analysis captures the dynamic nature of the project critical path and can determine concurrent delays with ease. By utilizing TIA to forecast a delay impact and Windows Analysis for determining exactly what occurred after the fact, both the contractor and the owner can assure themselves of the reasonableness of the impacts and the actual project delays. Additionally, in contrast to TIA, the Window Analysis method does not require the contractor to prepare fragnets with the impacted activities. Window Analysis compares the planned activity duration with the actual duration for a specific period of time. Thus, the analysis criterion is based on contemporaneous project documentation and, thereby, avoids assumptions and subjectivity as to "what should or might have happened." One of the biggest advantages of the Window Analysis method is that by utilizing each schedule for the period until a new situation arises (that changes the base logic and the identified critical activities), the analysis is always looking at "the then critical work" and therefore captures the project dynamics.

Benefits of Window Analysis to Monitor Project Progress
Although the Window Analysis method is frequently performed towards or at the project’s end, this technique can also prove beneficial if performed on a regular monthly basis during the project’s execution with the use of the updated monthly schedules. Performing a Window Analysis at the end of a project is a time consuming process. In case of a claim, both parties can incur significant legal fees while trying to settle their differences. Windows Analysis has been proven extremely powerful and most widely recog­nized in the construction industry and by legal authorities. Window Analysis utilizes the actual project schedules developed and submitted to the owner for the works. Delay is determined based on actual project documentation and assumptions which employ subjectivity as to "what should have happened" are not made. Each window can start with the contemporaneous plan for the future work based upon the previous month’s updated schedule and ends when the current month’s update schedule. This "window in time" is defined by the calendar period between these schedules, most likely one month in duration. This is extremely important as critical path activities determine the project completion date. Through the use of current schedules, the "reality" of the project at the time delays were occurring is analyzed and the method used by the contractor and owner in managing those delays is addressed. Window Analysis creates a mechanism whereby these schedules and their updates can be reviewed in a manageable and ultimately more useful manner. Another benefit of using Windows Analysis during the project execution is that the analysis can reveal the existence of potentially flawed or manipulated schedules that can surface while performing the delay analysis.

Summary
Critical path delay analysis techniques are widely applied in the construction industry, with the Windows Analysis method being regarded as technologically advantageous. TIA has proven to be a powerful forecasting tool for potential delays and for time extension negotiations. However, the assumptions that a contractor makes in determining the extra work can be subjective. Windows Analysis has been proven to be a powerful tool in the forensic determination of “what happened.” By combining these two techniques, both the contractor and the owner can assure themselves of fair and reasonableness of the actual project completion delays. The use of Windows Analysis on a monthly basis utilizing a month of duration between the schedule updates is also powerful in attempts to mitigate the potential of future claim and to documents the actual delays and impacts to the project completion activities, including causation and responsibility.

References:
1. Galloway, P., Nielsen, K.R. and Ramey, M., “Delay: Use of CPM Schedules for Concurrency, Allocation, Proof, and Analysis.”
2. Ciccarelli, J. and Cohen, M., “Window Analysis: The Method and the Myth,” 2005 AACE International Transactions.
3. Griffith, A., “Scheduling Practices and Project Success,” 2005 AACE International Transactions.
4. Zack, J., “Schedule Delay Analysis, Is there Agreement?” James G. Zack, Jr., 2003, Presentation.
5. Douglas, E., “Documenting the Schedule Basis,” 2005 AACE International Transactions.
6. Pickavance, Keith. “Delay and Disruption in Construction Contracts,” Second Edition, LLP Reference Publishing, London (2000).
7. Wickwire, Jon M., Driscoll, Thomas J., Hillman, Scott B., and Hulburt, Stephen B., “Construction Scheduling: Preparation, Liability, and Claims,” Second Edition, Aspen Publishers, New York (2003).

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Kentucky Society of Professional Engineers 2008 Annual Convention
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