Practice Standard for Work Breakdown Structures

1. WBS: The Deliverable-Oriented Project Scope Definition

A deliverable-oriented hierarchical decomposition of the work to be executed by the project team to accomplish the project objectives and create the required deliverables.

Defining project scope. The Work Breakdown Structure (WBS) is the fundamental tool for defining and organizing the total scope of a project. It breaks down the project's final outcome into smaller, more manageable components, focusing specifically on the deliverables that must be produced. This hierarchical structure clarifies "the what" of the project, not "the how" or "the when."

Hierarchical structure. The WBS arranges project deliverables in a parent-child relationship, starting with the overall project at the top level. Each descending level represents an increasingly detailed definition of the work. This structure provides a clear visual or textual outline of the project scope, making it easier to understand and communicate to all stakeholders.

Foundation for management. By defining the project scope in terms of deliverables, the WBS provides a solid framework for subsequent project management processes. It serves as the basis for:

• Activity definition
• Schedule development
• Cost estimating
• Resource allocation
• Risk identification

2. The 100% Rule: Ensuring Total Project Scope Inclusion

This rule states that the WBS includes 100% of the work defined by the project scope and captures ALL deliverables—internal, external, and interim—in terms of work to be completed, including project management.

Completeness is critical. The 100% Rule is a cornerstone principle of WBS development, ensuring that the WBS encompasses every piece of work required to complete the project successfully. This includes not only the final products or services but also all intermediate deliverables and the work of project management itself.

Applies at all levels. This rule is applied recursively throughout the WBS hierarchy. The sum of the work represented by the child elements at any given level must equal 100% of the work of their parent element. Crucially, the WBS should not include any work that is outside the defined project scope, preventing scope creep.

Work packages. The lowest level of the WBS consists of "work packages." These are the smallest components of work that can be effectively managed, scheduled, cost estimated, monitored, and controlled. The activities required to complete a work package must also sum up to 100% of the work for that package.

3. WBS: The Essential Input for Integrated Project Management

The WBS is a primary input to other project management processes—for example, resource planning, cost estimating, schedule development, and risk identification.

Integrating project functions. The WBS is not a standalone document; it is deeply integrated with and foundational to many other project management processes. Its deliverable-oriented structure provides the necessary framework for detailed planning and control across various knowledge areas.

Key process inputs. The WBS serves as a critical input for:

• Scope Management: Further defining and controlling the project scope.
• Time Management: Defining activities based on work packages.
• Cost Management: Allocating costs to specific deliverables and work packages.
• Human Resource Management: Assigning accountability for work packages.
• Risk Management: Identifying risks associated with specific deliverables.
• Procurement Management: Defining deliverables to be procured.

Foundation for control. A well-defined WBS enables effective monitoring and control throughout the project lifecycle. It provides logical points for measuring performance, tracking progress, and managing changes. Without a solid WBS, integrating these functions becomes significantly more challenging.

4. Defining WBS Quality: Core Characteristics for Every Project

There is a set of core characteristics that must be present in every WBS, as these characteristics enable the WBS to satisfy project needs that are present in every project.

Minimum quality standard. Core characteristics are the non-negotiable attributes that a WBS must possess to be considered a quality WBS. Their presence ensures the WBS can fulfill the basic requirements of defining and communicating project scope effectively, regardless of project type or industry.

Essential attributes include:

• Being deliverable-oriented and defining project scope.
• Clearly communicating scope to stakeholders.
• Containing 100% of the defined work.
• Capturing all internal, external, and interim deliverables.
• Having a hierarchical structure with a clear coding scheme.
• Containing elements defined using nouns, not verbs.
• Being created by those performing the work, with SME input.

Enabling project needs. These core characteristics ensure the WBS provides a clear, complete, and understandable representation of the project's scope. This clarity is essential for accurate planning, effective communication, and establishing a baseline for control.

5. Defining WBS Quality: Use-Related Characteristics for Specific Needs

There is an additional set of use-related characteristics that may vary from one WBS to another.

Tailoring the WBS. Use-related characteristics are flexible attributes that are adapted based on the specific needs of a project, organization, or industry. The quality of a WBS in this context is measured by how well its specific content and structure meet these unique requirements.

Situational adaptations:

• Level of Detail: Decomposed sufficiently for management, balancing control cost and manageability.
• Communication Detail: Providing enough detail for conceptualization and clarity, supported by a WBS Dictionary.
• Tracking Appropriateness: Suitable for required performance reporting levels.
• Control Appropriateness: Balancing complexity, risk, and the need for control points.
• Inclusion of Specific Elements: Incorporating elements for integration, procurement, training, etc., as needed.
• Accountability Assignment: Enabling clear assignment of responsibility at the appropriate level.
• Logical Structure: Organized in a way that makes sense for the project and organization (e.g., by phase, system, or geography).

Meeting project requirements. A high-quality WBS is constructed to meet all the specific needs for which it was developed, even if not all potential use-related characteristics are fully utilized. This adaptability ensures the WBS is a practical and effective tool for managing diverse projects.

6. Creating a WBS: Methods and Iterative Development

The WBS evolves through an iterative consideration of the project’s purpose and objectives (both business and technical), functional and performance design criteria, project scope, technical performance requirements, and other technical attributes.

Multiple creation approaches. A WBS can be developed using various methods, including starting from scratch with top-down or bottom-up approaches, reusing components from similar projects, or utilizing organizational templates and standards. The chosen method should align with project objectives, requirements, and organizational practices.

Common methods include:

• Top-Down: Starting with the final product and progressively decomposing it. Good for brainstorming and when scope is less defined.
• Bottom-Up: Identifying all work packages first and then grouping them hierarchically. Useful when deliverables are well understood or using templates.
• Organizational Standards/Templates: Reusing predefined structures or guidelines. Promotes consistency but requires customization.

Iterative refinement. WBS development is inherently iterative. It should be reviewed and revised as project planning progresses and more information becomes available (progressive elaboration). Once the scope is baselined, updates should follow a formal change control process to maintain alignment with project changes.

7. Essential Judgments for Appropriate WBS Detail

The level of detail in a WBS is a function of the size of the project, and reflects a balance between complexity, risk, and the project manager’s need for control.

Balancing detail. Determining the appropriate level of decomposition requires judgment based on project-specific factors. The goal is to break down deliverables sufficiently to enable effective planning, management, and control without creating excessive overhead for tracking and reporting.

Factors influencing detail:

• Scope Clarity: Is the WBS element clearly understood?
• Measurability: Can progress be objectively measured?
• Dependencies: Do internal deliverables have different prerequisites or external relationships?
• Accountability: Can the work be assigned to a single accountable individual?
• Risk: Are there specific risks requiring focused attention or more accurate planning?
• Estimating Accuracy: Is more detail needed for reliable cost and duration estimates?
• Reporting Needs: Are stakeholders interested in tracking status of only a portion of the element?

Progressive elaboration. For larger or less defined projects, the WBS may initially be detailed only for the near-term work (rolling wave planning). Further decomposition occurs later as more is known. Not all branches need to be decomposed to the same depth; detail should be driven by the needs of each specific area.

8. Evaluating WBS Quality: Avoiding Common Pitfalls

Project failures, however, can often be traced back to a poorly developed or nonexistent WBS.

Consequences of poor WBS. A poorly constructed WBS is a significant risk factor for project failure. It can lead to unclear scope, missed work, inaccurate estimates, budget overruns, schedule delays, and confusion among team members.

Common WBS defects:

• Not deliverable-oriented (structured by process or activity instead).
• Incomplete scope (missing deliverables).
• Including work outside the project scope.
• Elements defined using verbs instead of nouns.
• Overlapping responsibilities for elements.
• Insufficient detail for planning and control.
• Excessive detail leading to unnecessary overhead.
• Not updated when scope changes occur.

Checklist for quality. Evaluating WBS quality involves checking for core characteristics and assessing whether use-related characteristics are appropriate for the project's needs. Using checklists and involving stakeholders and subject matter experts in the review process can help identify and correct defects early.

9. WBS Application Across Projects, Programs, and Portfolios

There is no conceptual difference among a project WBS, a program WBS, or a portfolio WBS.

Scalability of the WBS concept. The fundamental principles and characteristics of a WBS apply equally to projects, programs (collections of related projects), and portfolios (collections of projects and programs aligned with strategic objectives). The difference lies primarily in the breadth of the scope being defined.

Higher-level WBS:

• Program WBS: Organizes the scope of a program, which includes related projects and potentially other program-specific work. It illustrates the relationship among projects and program-level deliverables.
• Portfolio WBS: Organizes the scope of a portfolio, grouping projects and programs to facilitate strategic management. It may not imply direct interdependencies between elements.

Consistency is key. Regardless of the level, a high-quality WBS at the program or portfolio level possesses the same core and use-related characteristics as a project WBS. However, verifying completeness and detail becomes more challenging as the scope increases. Using WBS consistently across all levels supports integrated management and strategic alignment.

Last updated: May 15, 2025