A work breakdown structure (or WBS) identifies all of the tasks required to finish a project, usually in a hierarchical structure. It is basically a glorified TODO list, but it is one of the most powerful tools a project manager has. This is because a WBS helps to provide a detailed illustration of the project’s scope, can be used to monitor progress, aids in creating accurate cost and schedule estimates, and builds project teams in that that it gives team members a sense of how his/her work fits into the overall effort.
The WBS is built from the top down. The project is broken up into the various deliverables, which are in turn broken down into the particular tasks needed to produce those deliverables. Only the lowest-level tasks are called “work packages” – anything in the chart that contains subordinate tasks is called a “summary task“. Summary tasks are never actually executed – they become complete through the progress of their work packages. Each work package (lowest-level task) should follow these rules of thumb:
- The 8/80 rule – No task should be smaller than 8 labor hours or larger than 80.
- The reporting period rule – No task should take longer than the distance between two status points (i.e. if you have status meetings every week, no task should last longer than one week).
- The “if it’s useful rule” – Only break a task down further if it makes the task easier to estimate, easier to assign, or easier to track. If it won’t do any of these, don’t break it down further.
Here are the major steps needed to build a WBS:
- Begin at the top – List the major deliverables or high-level tasks from the scope statement.
- Name all the tasks required to produce those deliverables – Turn the deliverables into tasks by adding a strong verb in front of them (e.g. “Shrubs” -> “Plant the Shrubs”) and then break them down into lower-level tasks. This is harder than most people think. If there is trouble doing this, it is a sign that a small meeting of top-tier people is needed to help break it down. It might also be a good idea to give a task to an expert in the subject and have him/her break it down for you. Even if this process takes a long time, it is worth it in the long run. Projects often run into “blind alleys” if a clear WBS is not made early on.
- Organize the WBS – It is possible to rearrange the work packages in different formations, which could emphasize different aspects of the project. Move the tasks around and group them under different summary tasks until the WBS is meaningful to the people involved.
Three more guidelines:
- The WBS must be broken down from the top. It is crucial to ensure than work packages are subsets of their summary tasks.
- Work packages must add up to the summary task. Don’t omit tasks; it becomes much harder to estimate costs and time if the WBS is not complete.
- Each summary task and work package must result in a concrete product. Don’t be vague or unclear. “Do research” is weak and is open-ended. “List candidate vendors” is more concrete.
