6

PROJECT SCHEDULE MANAGEMENT

The Project Schedule Management section of the PMBOK ® Guide is applicable to construction projects. This section of the Construction Extension presents additional considerations for planning, and monitoring and controlling the schedule on construction projects.

The construction industry is one of only a few industry sectors that involve the meticulous detail of Project Schedule Management. The scheduling method, the level of detail, the project parameters, and the planning factors all should be considered and demonstrated as defined by the contract conditional requirements. In addition to standard scheduling practices, Project Schedule Management in construction includes details for schedule management plan development; levels of detail for activity definition; requirements for resource, cost, and risk-loaded activities weightage definition; progress curves; monitoring and schedule control procedures; and conditions for owner acceptance or approval. The schedule management plan sets the early tone for the project framework to satisfy the contractual requirements, while progress monitoring and schedule control provides the mechanism for contractor progress payments and to deliver the project within the required completion date as stipulated in the contract.

6.1 Project Schedule Management in Construction

Project Schedule Management in construction involves complex challenges mainly due to the magnitude of stakeholders involved such as the owner, prime contractor, subcontractors, vendors, material suppliers, end users, regulatory agencies, etc. Some of the factors that give rise to this complexity are:

• The vast number of activities and their durations that need to be scheduled such as procurement and installation of equipment and materials, contract submittals, approvals, and performance inspections, procurement bidding process, and contract execution;
• Types of relationship between activities with leads and lags and complex interrelationships between work sequences and material interfaces;
• Integration of schedules from a multitude of stakeholders that are both directly and indirectly involved in the construction performance;
• Activity durations for periods of time for contingency due to potential lost time as a result of inclement weather conditions and material installation restrictions;
• Level of detail in different types of schedules such as master project schedule, weekly contractor work activity schedules, two-week look-ahead schedules; and
• Monitoring and controlling construction and administration activities for all of the involved stakeholders.

The complexity of the schedules, the unique interrelations between construction activities, and the need to interpret and understand the process makes construction time management different from that of other industries due to the greater need for more detailed planning and elevated technical analysis. Construction predominantly uses the critical path method (CPM) for its scheduling practice. Its use is often the focus of contract claims due to project time impacts and delays to the contract completion.

Scheduling in construction is a complicated and serious effort with a major contract clause being “time is of the essence.” Should the project fail to be completed within the contract completion, consequential damages and project cost impacts may be incurred by the stakeholders. Multiple contractors are involved to ensure the facility is completed on time; otherwise, an owner unable to occupy the facility may incur an impact to its source of revenue or other commitments toward the public and private stakeholders. The general contractor has the overall responsibility to meet the owner's completion milestone. If the general contractor does not complete on time, it may be assessed liquidated damages as spelled out by the construction contract.

Other schedule management considerations in construction include:

• Number and type of resources needed for each project activity;
• Existing and imposed environmental site conditions and regulations;
• Influences of weather conditions;
• Scheduling method;
• Constructability or critical sequence constraints, including partial use by the owner or public for infrastructure projects like roadways;
• Allowances for owner-occupied facilities during construction;
• Considerations and potential impacts on external stakeholders and social groups;
• Time and work access constraints to avoid impact on the environment and satisfy regulatory requirements;
• Restrictions arising from third parties such as permit and design approvals, and right of way acquisitions;
• Availability and procurement time factors for specialized contractors, equipment, and material;
• Requirements for labor, material, and equipment; and
• Local, state, federal, and international regulations.

6.2 Project Schedule Management Planning

Contractual requirement documents often dictate the components of the schedule and the requirements for activity definition, resources, cost loading, and performance evaluation. These documents should be reviewed thoroughly when preparing a schedule management plan. A pre-project planning outline should be required for all project owners and should be created for every project. The outline serves as a baseline for progress reporting and is often used to judge the final success of the project delivery. Pre-project planning should:

• Be driven by the owner and contract,
• Include clearly defined roles and responsibilities,
• Include users such as operations and maintenance, and
• Start as early as possible.

The construction organization should keep a central repository of all schedule information and records of previously executed projects so as to reduce the amount of effort required to recreate this information for each new project. This central repository may include all of the documents, templates, policies, procedures, plans, guidelines, historical data, cost information, schedule metrics, and risk assessments. All members of the project management team should have easy access and use of these repositories.

6.2.1Define Activities

The project management plan defines the decomposition process to identify the activities required by the project team to complete the project deliverables, which may include the project scope statement and work breakdown structure (WBS). A structured view breaks the project deliverables into manageable work packages, and defines what should be delivered to achieve the project objectives. Examples include work performance activities that generate an activity list along with their activity attributes, and possibly, a milestone list.

Performing organizations may utilize activity templates from previous projects. For example, on a housing project, a contractor may identify activities such as excavation, concrete foundations, wall framing, drywall and painting, and door and window installations, and only adjust the durations based on building size and quantities.

When defining activities and choosing tasks—particularly tasks to be performed by subcontractors—task interconnections, interdependencies, and the possible emergence of new conditions as a result of such interdependencies should be considered possible risks. Examples may include all testing of pipes and electrical systems to be completed prior to insulation and closure of the work space. Many contracts also list intermediate milestones for certain completions or facility turnover.

6.2.1.1Work Breakdown Structure

The WBS used in scheduling should fully address the entire project scope and contract requirements. To be consistent in addressing the cost, risk, and resource aspects, the WBS should be integrated to meet time, cost, and responsibility commitments. As in most industries, the WBS can form the foundation for all subsequent planning and can extend several steps further by incorporating the multiple contractors and many contract requirements for proper administration and execution of the construction works.

6.2.1.2Decomposition

The level of detail is a key consideration on most projects. Schedule activities broken down into too small components can lead to an unmanageable level of detail. Construction-specific indicators for decomposition will often describe the minimum viable level of detail measured by units of work, work weeks, work days, or work hours. The level of detail should be appropriate for the particular project and capable of producing project reports at different levels per stakeholder requirements. These hierarchical schedules will serve to address the different stakeholders and their needs for schedule information such as:

• Owner summary schedule,
• General contractor's master schedule,
• Submittal and procurement schedule,
• Resource and subcontractor schedules,
• Three-week look-ahead planning schedule, and
• Superintendent's weekly workforce planning schedule.

6.2.1.3Activity Attributes

Activity attributes—characteristics that are common for a group of activities—include durations, costs, labor hours, and quantities. Attributes may also be determined by the contract.

The activity attribute should be used when determining the activity weights for each level of the WBS. In the first level of the WBS, the attribute is usually the deliverable cost. When the decomposition level is sufficient to identify another attribute that is common to all activities in that level, then that attribute should be used. When the decomposition level reaches project activities, there is usually more than one common attribute, and expert judgment is needed to determine which attribute to use. The scheduler's experience and expert judgment are considerable assets for the construction organization. The attributes determine the weight of each project deliverable or activity (Section 6.2.5). A summation of those attributes can be made and transformed into a percentage for tracking construction progress.

6.2.1.4Progress Measurement Plan and Criteria

A progress curve management plan describes how progress will be measured and monitored for actual progress calculations. It may also describe how changes to the progress curves will be managed, but these usually result from schedule changes. It may be formal or informal, highly detailed or broadly framed, depending on the needs of the project.

Progress measurement criteria are the components used to determine how progress is measured for an activity. Preestablished progress measurement criteria are used to avoid conflict among stakeholders when assessing project progress. In construction, physical quantities such as concrete or steel are measured to ascertain project progress. Documentation (e.g., site logs) is also checked to verify progress and validate or approve progress payment for contractors.

6.2.2Sequence Activities

Sequencing activities identifies and documents relationships among project activities and should reflect the construction strategy. Activities should be sequenced in a logical manner, determining predecessors and successors. The type of relationship, such as finish to start, should also be determined with leads or lags, where required. Proper sequencing is necessary and requires the participation of experienced construction personnel and individuals proficient in the use of scheduling software. Sequencing examples include:

• Specific excavation in close proximity to an existing structure and the placement of foundations before backfilling operations;
• Concrete form removal and water containment structures may have a lag time to account for concrete curing and water leakage testing;
• Specialized equipment and material installations linked with a procurement schedule; and
• A contract stipulation requiring the transfer of the facility to the operational owner by a fixed contract date.

In construction, most sequencing is displayed using commercially available scheduling software. Technology developments, such as specialized 4-D software, makes it possible to incorporate the project design plans to semi-automatically develop the schedule layout, activity durations, and logic relationships.

The linear scheduling method (LSM) is often used on linear projects such as highways, pipe and transmission lines, or tunnels. The station or mile post numbers depict the physical location of the work; activities are visually represented at a physical location. Figure 6-1 helps in understanding and tracking the flow of work and may aid in identifying progress of the work when actual progress is depicted on the same schedule. LSM is also referred to as line of balance, time–location, or distance–location scheduling.

6.2.3Estimate Activity Resources

A contractor estimates the resources needed to complete each activity. These resources can be equipment, material, or human resources. Excavation may need a backhoe with an operator; roofing may need a roofing crew with quantity of roofing material to be used. Contractors generally use historical records for activity resource estimates, along with the team's past experience, but may also use industry publications that provide resource estimates in a parametric fashion. The manner and method used is often a final choice depending on the construction knowledge and experience of the organization.

Activity resources and supplementation for peak levels is a source of contention in construction, especially with at-risk contracts. This is often due to stacking of trades, which can reduce productivity and create resource inefficiencies without improving the schedule duration. Research has shown that there are many instances where adding labor not only resulted in wasted effort but generated adverse effects for the particular activity. Diligence and experience is imperative when deciding to supplement activity human resources. Section 9 on Project Resource Management provides additional information for this consideration.

Resource breakdown structures (RBS) and resource calendars are often established for key resources such as tower cranes, excavators, backhoes, equipment operators, and specialized construction crews. A construction operation, such as steel erection above other construction trades, is a significant safety concern and influences the decision on effective resource scheduling. Project cost estimating is closely linked with estimating activity resources as the type and use of resources form a large portion of the overall project cost.

6.2.4Estimate Activity Durations

Duration estimates indicate the number of work periods needed to complete an activity based on anticipated resource availability. These work periods are most often in hours, days, or weeks. Depending on the stage of the schedule development, the project estimator or construction superintendent may review the design drawings and associated work to be performed and compare it with the budget and time constraints (a form of parametric estimating) to determine the activity duration. The superintendent may refer to historical records (analogous estimate) for a comparison or may base the estimate on experience, while also considering expected productivity of each resource. Given the complexity and uncertainty of the risk considerations for the expected activity duration, additional estimating factors may be considered to allow for mitigation or contingency actions. Activity duration estimating may also include an analysis of the total project duration as a function of project or management reserve for unanticipated or unknown risks.

On certain plant maintenance projects, often called turnarounds or shutdowns, work periods may be established in minutes due to the critical nature of getting the plant back online and the sequence of operational start-up requirements. Some turnarounds can have around-the-clock (24-hour) scheduling utilizing three work shifts with progress updates occurring every 8 hours.

6.2.5Activity Weightage Definition

Activity weightage is the evaluation of activity characteristics and attributes for the purpose of assessing the contribution of each activity to the overall project. Activity weights can be assigned to the overall progress or to the progress of a given phase or deliverable of the project. Examples of activity weights can be units of production such as lineal feet, metric tons, resource material quantities, and activity cost including equipment, material, and labor. Activity weights are used to determine the planned and earned values for earned value management and to make progress payments for work performed. Relative weights are often calculated as a percentage of the relative weight's contribution to the project. Absolute weights are the weight of an activity represented by its specific or absolute value contribution to the overall project.

6.2.6Develop Schedule

Developing the schedule is the process of analyzing activity sequences, durations, resource requirements, and schedule constraints to create the integrated schedule model, which generates the project schedule. Developing the schedule model is an iterative process involving numerous stakeholders, sometimes with contrasting interests and intent. Incorporating these components is a challenge to establishing the baseline schedule. The level of detail becomes a key attribute for activity consistency on major projects involving many stakeholders. Historical data gathered from lessons learned from previous projects often aid the scheduling effort for subsequent projects.

6.2.6.1Vendor or Subcontractor Schedule Analysis

It is necessary to consider the potential impacts of the additional constraints that subcontractors and vendors have on the integrated project schedule. For example, stacking of trades sometimes occurs when several trades (i.e., electricians, painters, plumbers) perform work in the same area at the same time. It is important to analyze subcontractor schedules for scope verification, material or equipment delivery dates, crew size, and activity dependencies that may cause stacking or physical constraints.

The need for schedule development flexibility is important as the vendor and subcontractor elements become evident. For example, excavation for underground work may restrict or prevent the access to some areas. Similarly, scaffolding for elevated works may restrict or prevent access to working below the scaffolding in some areas. These situations create a need for finding alternative solutions such as changing activity sequencing, staggering subcontractor work hours, or adjusting available work areas at specific time periods.

6.2.6.2Constraints

A typical construction project may contain multiple contract milestones. These may include specific events that are contractually fixed and are considered constraints. In addition to availability windows (e.g., access restrictions, equipment availability, and environmental regulations), a number of other constraints should be integrated. For example:

• Imposed dates and major milestones. An interim construction phase or project completion date is an example of an imposed fixed date on construction contracts, and is usually a significant constraint. The date when all contract scope is turned over to the client is referred to as the substantial completion. A post-project completion date is often after substantial completion, and is called the final acceptance date or contract completion. This is the point in time when the contract is closed and only equipment and facility warranty aspects may remain.
• Statutory requirements. Development of the schedule should consider all limits, restrictions, or other obligations placed on the project by municipal, regional, national, or international regulations. For example, there may be load limits on road travel during certain times of the year or migratory habitat restrictions. Further, possible time contingencies should account for the incorporation of potential risk events.
• Weather. Construction is often exposed to the elements of nature. Weather conditions can affect the performance of materials and installation efforts. The schedule should integrate planning to avoid the weather constraints that could affect certain construction operations.
• Inspections, approvals, and permits. Activities and processes by third parties should be integrated for submittal approvals. Building and access permits and construction inspections are all contingent constraints affecting the schedule.

6.2.6.3Schedule Baseline

A schedule baseline is the approved version of the schedule model and is one of the most important documents in time management. Schedule progress is measured against the contract and schedule milestone dates. The baseline is an important reference document if contract and progress delay disputes arise between stakeholders.

6.2.6.4Use of Metrics

Metrics play an important role in schedule management for construction. Metrics from previous projects (e.g., actual activity durations, productivity, and labor hours) can be gathered as an input for preparing a resource estimate. Schedule time and cost growth are common performance metrics used in construction, which can provide a snapshot of construction progress.

6.2.6.5Schedule Dictionary

A schedule dictionary includes supporting documentation that provides a clear and complete description of how the schedule was derived. Information used may include, but is not limited to, production rates, level of accuracy, exclusions, and assumptions. Most scheduling software includes additional data fields for each activity that can be used for this basis.

6.2.6.6Schedule Risk Analysis (SRA)

Schedule risk analysis establishes and validates schedule contingencies, identifies priority risks and risk-driven events, and continuously monitors for project-related risks. Risk events impact scenarios, and alternatives can assist in risk response to avoid schedule impacts and estimate the time needed for mitigation or contingency purposes. Monte Carlo simulation is useful for performing schedule risk analysis and planning scenarios for projects that are exceptionally critical in terms of project time and risks.

6.2.7Progress Curves Development and Update

Progress curves development is the creation of a progress baseline. This is created in a manner similar to a cost baseline. Progress is plotted against the baseline to provide a trend line that can be helpful to forecast future progress.

Progress curves are graphical representations of project progress and may be represented as follows:

• Early or late. Early progress curves are based on activities of early start and finish date calculations. Late progress curves are based on activities of late start and finish date calculations.
• Overall or partial. These graphs refer to a progress description that is represented for the overall project or for specific WBS deliverables. In engineering procurement construction (EPC) projects, progress curves are usually plotted for the overall project and the E, P, and C phases.

6.2.7.1Weights Distribution Standard Curves

Each activity weight is calculated based on a particular activity attribute, such as man-hours consumption, material, or cost applied. For example, the length of time for back filling an area is a function of the volume of soil deposited in that area; the soil deposition rate is determined by the equipment capabilities and is linearly distributed along the activity duration.

6.2.7.2Mathematical Analysis

Mathematical analysis is used to calculate the weight distribution along the project duration. Each activity has a weight and is utilized according to standard curves. Calculating the weight completed for each activity in a work period highlights the project progress for that work period. Repeating the analysis for all project work periods gives the overall project progress curve. Project management software is generally used to automate the process of performing a mathematical analysis.

6.3 Project Schedule Management Monitoring and Control

Control Schedule is the process of monitoring the status of project activities to update project progress and manage changes to the schedule baseline in order to achieve the planned project completion date. Documentation, such as site logs and daily/weekly progress reports, are checked to verify progress. Schedule updates are produced on a predetermined frequency as outlined in the schedule management plan. These are reviewed to evaluate any deviation from the baseline.

Progress monitoring is the evaluation of the actual project progress compared to the baseline in order to take preventive or corrective action. The evaluation includes examining the activities involved and their characteristics. The actual start and finish dates for project activities form the basis for actual progress calculations and document the as-built schedule information. Determining if previously implemented corrective actions have been effective is also a critical task in progress monitoring.

Schedule components that require progress monitoring are the critical path, the near-critical path, and noncritical path activities, generally considered all other work activities. If critical path activities slip, they will immediately cause project delay. If near-critical path activities slip, they could potentially become the critical path that delays project completion. If the mass work activities—noncritical path activities—slip and are not progressed appropriately, they may cause trade stacking and space/location work area conflicts, and likely cause project delay. The components can be monitored by a variety of techniques such as float dissipation (erosion of float), missed start and finish dates, actual duration analysis, and earned value management.

6.3.1Progress Curve Updates

Progress curves are used as a basis for comparing the schedule baseline. A progress curve update indicates the progress information occurring in a work period. When the project schedule, WBS, or both are modified through integrated change control, the progress curves are revised to indicate the new progress curve information. Appropriate stakeholders should be notified as needed. Progress curve updates may or may not require adjustments to other aspects of the project plan.

Figures 6-2 is an example of an updated progress curve depicting the total float on the updated baseline schedule and the status schedule with respect to the project substantial completion.

6.3.2Schedule Impacts

Unplanned situations occur for a variety of reasons and impact the construction schedule (e.g., the emergence of unforeseen new issues or changes in known or unknown conditions on the project site). These changes should include the quantification of the impact on project time, cost, and resources. Contractors often have to demonstrate to the owner the need for time extensions by providing a detailed schedule analysis. This may involve a complex and comprehensive review and comparison using one of several techniques, such as comparing the as-built and the as-planned schedule. There can be consequential effects that should be evaluated, which could require changes to the project or may result in claims.

Organizations should have in place the knowledge and industry-recognized scheduling practices when it comes to documenting and evaluating a schedule impact situation. These practices are essential for assessing and presenting the outcomes through a change request and integrated change control in order to avoid unwanted construction claims.

6.3.3Progress and Performance Reviews

Progress and performance reviews compare schedule performance over time and are often used in conjunction with contract progress payments. Success factors in time management reflect the effective use of change management. Controlling the ramifications of changes to the project baseline is done through the use of special techniques, such as time impact analysis (TIA). This technique is used with critical path methodology (CPM) schedules by producing an up-to-date model of the construction plan, inserting activities designed to model the changed condition, adding appropriate logic, and recalculating the schedule. The difference in milestone completion shows the impact of the changed condition on the baseline milestone time frame (see also Section 10.4.1).

One of the main sources of claims is the failure to provide timely and accurate analysis for time extension requests, even when the contractor is entitled to a time extension. A rejection of a requested time extension may be due to inappropriate submissions by contractors, but may result in a breakdown in the relationship between the owner and contractor. These breakdowns commonly show up in claims, so it is important that all parties deal with requests for extensions of time in a fair and timely manner.