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What is a WBS (Work Breakdown Structure)

What is a WBS (Work Breakdown Structure)

The WBS stands for Work Breakdown Structure. It is the structure that organizes a project’s deliverables into separate identified elements. Specifically, from the PMBOK Guide, Work Breakdown Structure is “a hierarchical decomposition of the total scope of work to be carried out by the project team to accomplish the project objectives and create the required deliverables”.

All of the work needed to accomplish the project is contained in the project’s scope baseline, which is made up of the scope statement, WBS and the WBS Dictionary. But, the WBS is created by those doing the work. In order to create the WBS, the Project Manager needs to reference the:

The WBS encompasses all of the work needed to perform for what you’re getting paid to do. “Scope creep” would be any work asked to do (for free) not identified within the WBS. The WBS starts from the Scope Statement which should describe “what is” and “is not” included with each work element. A WBS is a brief description of the work using nouns and adjectives, not verbs. A WBS Dictionary provides detailed information about the component activity and scheduling information. 

Another way to think about a WBS is that it clarifies the work to communicate project scope. The decomposition of the WBS should contain at least 2 levels. A WBS is also effectively done when it is time-phased. The components that happen first in the project should come first in the WBS structure. A network diagram can help with this.

To illustrate how a WBS is done, let’s build a house. Assume the following construction work components for a house were the scope of this project:

  • Primary Structure
  • Electrical
  • Plumbing
  • Inside Walls

This would probably be the order in which to build by a network diagram. Electrical and Plumbing cannot be started on until the structure of the house is finished and the inside wall finish can be started after that. These deliverables only need to have more structure and definition added. “Primary Structure” could probably deal with a lot of things, so it should contain another couple of levels describing the elements that it consists of. Such as:

Primary Structure :

  • Foundation
  1. Topography
  2. Excavation
  3. Cement Pour
  • Exterior Walls
  • Roof

 Again, this is probably the order in which they are done. Exterior Walls is done after Foundation and Roof is done after the walls are put up. The House Build WBS could be the following:

House Build

1. Primary Structure

a) Foundation

  • Topography
  • Excavation
  • Cement Pour

b) Exterior Walls

c) Roof

2. Electrical

3. Plumbing

4. Inside Walls

Note that these components are not activities to be done. The activities and resources required to achieve results can be located in the WBS Dictionary.

Eventually, these WBS components should combine with an OBS structure to create control accounts. An OBS is an Organizational Breakdown Structure that highlights staffing levels. A control account is a charge number that someone would use to identify the work that they are supposed to be doing.

In summary, creating a WBS in this way facilitates change control and provides easy reference with program scheduling and documentation for vertical and horizontal traceability. Vertical traceability describes the interdependence among project documents, such as the SOW and the IMS (Integrated Master Schedule). Horizontal traceability describes the relationship logic of how the components are scheduled with each other.  

Author - Gregory Morrow

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