Work Breakdown Structure (WBS): Top-down or Bottom-up?


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A work breakdown structure (WBS)is the key element to defining the project strategy. It is the foundational element of planning upon which everything else will be built, alongside the RACI, timeline, and project team.

Let’s consider it the framework of the project. Getting the framework right is the first step in assuring you have the right scope defined. The Work Breakdown Structure is essentially a hierarchical view of all deliverables or tasks needed to complete a project. The tasks at the lowest WBS level define units of work that can be defined. This level of work can also be accurately estimated in terms of the durations, resource needs and costs.

There are many different types of work breakdown structures, but there are two key ways to create them regardless of type: the top-down approach and the bottom-up approach.

Top-Down Approach

The top-down approach starts from the largest deliverable (the project outcome) and continues to break it down into smaller deliverables typically by topic or function areas and workstreams. It’s then broken into smaller deliverables, also called the work packages and sub tasks or activities.

The top-down approach is a logical approach that starts by working from the largest outcome and dissecting the smaller deliverables and tasks to get there. The top-down approach usually requires knowledgeable persons that have an overarching awareness of what is needed at a high level to bring the deliverable to fruition.

To create a highly useful top-down WBS, bring together a team of subject matter experts and decompose the project outcomes and deliverables. If there are five — for instance, application functionality, a new graphic user interface, new processes, and legal and compliance signoff — take each of those and break it down further into the deliverables required from each area. Then, go one layer lower to determine the key tasks and activities to bring those to fruition.

Be sure to note which department is responsible for those deliverables and tasks. Also be certain to clearly note what each deliverable or task is, so everyone knows what those are three months later when persons may have forgotten, left the company, or moved to another role.

While the top-down approach is seemingly the most beneficial approach, it is dependent on knowledge. An organization may be new and thus not have the in-house knowledge needed, or an organization may have lost through attrition key subject matter experts.

Another challenge with this approach could be that the subject matter experts with the knowledge of high-level deliverables and tasks may not have intimate working level knowledge of the details or smaller tasks, which could cause a critical gap or timeline concern if not planned. These could be newer persons to the organization that know how to complete a certain type of project but do not know the intricacies of the culture of the organization.

Bottom-Up Approach

The bottom-up approach is more of a brainstorming exercise, during which individuals from the different involved teams share activities that need to be completed. This is more of a running list of tasks than a structured review of how each task is decomposed.

To use the bottom-up approach, the project manager would need to think through all involved parties and then invite all to a large workshop or request the list of activities via email. To make the approach more useful, it would be helpful to request not only the details about the activity but also who is involved in each activity and what the outcome is.

This approach is less structured and lacks logical sequencing and thus could be more prone to having gaps. This approach also may not arrive at the lowest level, as it can sometimes be unclear what level the tasks being shared are and what work packages they are aligned to.

While this approach is prone to gaps, the broad brush brainstorming can lead to uncovering tasks that might have been forgotten or assumed during top-down, as the key stakeholders may not have insight into some of the low-level details and tasks.

Additionally, in an organization where the type of project has not been done before or there is no in-house subject matter expertise, the bottom-up approach could be helpful to craft the story of what is needed and the expertise that will be needed to craft the full picture of those needs.

Hybrid Approach

While some gravitate to an all-or-nothing approach, a combination of both approaches can lead to the most accurate WBS. For the hybrid approach, start with the top-down approach, logical organized decomposition based on key subject matter experts, project manager knowledge, organizational assets and historical project information, and department and functional leads. Use this detail to craft the shell of the WBS.

Then, share the draft WBS with additional organizational persons that are more involved in the details of similar functions or department activities. Inquire with them via email or meeting if within each aspect of the WBS, all of the tasks that they are aware of are noted. If not, add that into the WBS where it is most appropriate to have the most accurate picture of the work. Then, the bottom-up approach becomes more of a tool to validate that all of the activities are included and being planned for.

Finalizing the Approach

Now that the WBS has been created, whether via the top-down, bottom-up, or a mix, it is critical to have a final review with all stakeholders. Ensure all teams that the project or service will touch are included. An in-person or virtual review will be more effective than an email share. Yes, this will be another meeting, and participants may feel that they don’t have time, but truly the team doesn’t have time to miss out on including any aspects of the work.

Walking through component by component will likely draw attention to something that hasn’t been considered or isn’t a part of the correct workstream. The closer the current WBS is to being accurate, the more helpful it will be for future programs. The discussions will also bring out great details that will be key for the next step — turning the WBS into a project schedule.

Regardless of the approach to be taken, make it a general practice to use a standard template, and make this a part of your organization’s project management process.

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Latoya Morris, PMP, CSM, ITILv3 Avatar

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