Tasks and WBS outline levels in Microsoft Project

With a start date and a calendar in place, the Northgate owner's master schedule is ready for its first tasks. Before typing a single duration, the Owner's PM builds the skeleton: the work breakdown structure (WBS) as Microsoft Project summary tasks, indented into outline levels, with codes that will still mean the same thing at the last monthly report. This lesson shows how, using the ten-element Northgate summary WBS.

Learning outcomes

• Explain what a WBS is and how it maps to summary tasks and outline levels in Microsoft Project desktop.
• Build a three-level outline with Indent Task and Outdent Task, and collapse it by level for reporting.
• Tell the Outline Number field from a custom WBS code, define a WBS code mask, and renumber after a change.
• Apply simple rules for summary tasks, task names and milestone placement in an owner's schedule.

The lesson

What a WBS is, in one paragraph

The PMI® describes a WBS as a hierarchy that breaks the project's total scope into smaller pieces, organized around deliverables rather than activities. Two ideas from PMI's Practice Standard for Work Breakdown Structures do most of the work. The 100% rule: the WBS covers all of the scope and nothing outside it, and each element's children add up to exactly that element. Work packages: the lowest elements, each with an identifier and an owner, small enough to estimate and track. A schedule then hangs activities and milestones under the work packages.

How Project shows a WBS: the outline

Microsoft Project has no separate WBS editor. The WBS is the task outline:

• Summary tasks are the WBS elements. When you indent a task, the task above it becomes a summary task, and its bar rolls up the dates of everything beneath it.
• Outline levels are the depth. The project summary task (row 0, switched on in lesson 3) is level 0; the ten Northgate elements are level 1; their components are level 2; detail tasks and milestones sit at level 3. The Outline Level field shows the number, and Project calculates it.
• Outline numbers (1, 1.1, 1.1.1) are calculated from position. You cannot type them, and they change whenever you move, indent or outdent a task.
• WBS codes are a separate field. By default they copy the outline number, but you can define a custom mask with a prefix, and they do not renumber themselves when tasks move.

Building the outline, step by step

1. Show the structure. On the Gantt Chart view, go to Format > Show/Hide and tick Outline Number. The project summary task should already be on (lesson 3).
2. Type level 1. Enter the ten WBS element names in the Task Name column, one per row, in WBS order.
3. Insert and indent level 2. Select the row below an element, insert new rows (Task > Insert > Task), type the component names, select them and choose Task > Indent Task (Alt+Shift+Right arrow). The element above becomes a summary task. Outdent Task (Alt+Shift+Left arrow) moves a row back up a level.
4. Add level 3. Repeat under each component for detail tasks and milestones. Durations and links come in lessons 6 and 7; for now, structure only.
5. Collapse by level. View > Data > Outline shows Level 1, Level 2 and so on, or All Subtasks. Level 1 is the one-page owner's summary; Alt+Shift+Hyphen and Alt+Shift+Equal sign hide and show subtasks of a selected summary.

Microsoft notes two behaviours worth remembering. Moving or deleting a summary task moves or deletes everything under it, so outdent anything you want to keep first. And a summary task's cost and work are the sums of its subtasks, but its duration is not: it spans the earliest start to the latest finish beneath it.

Screenshot to come

Outline number or WBS code?

For a small file the outline number is enough. For an owner's master schedule that will be compared with a contractor's schedule, reported monthly and maybe used as evidence, a custom WBS code is better because it is stable. Go to Project > Properties > WBS > Define Code. The WBS Code Definition dialog box takes:

• a Project Code Prefix added to every code;
• a code mask, one row per outline level, each with a Sequence (numbers, uppercase letters, lowercase letters or unordered characters), a Length (a fixed number or Any) and a Separator (a period by default);
• two check boxes: Generate WBS code for new task and Verify uniqueness of new WBS codes. Leave both ticked.

The catch is in Figure 3. Project does not renumber WBS codes when you move or delete tasks. That is the point of a stable code, but after a real restructure, codes and positions drift apart until you run Project > WBS > Renumber for selected tasks or the entire project. Renumbering changes codes other people may already use in reports, so do it before the baseline, not after.

Rules for a clean outline

• Summary tasks are containers. Do not assign resources to them (Microsoft warns this can make overallocations impossible to resolve), and do not type durations or dates on them. Summary tasks give structure, not logic: link detail tasks, not summaries (lesson 7).
• Names carry their own context. Summary names are nouns (deliverables). Detail tasks are verb plus object (Pour slab-on-grade). Milestones state a condition (Foundations and slab complete). A filtered list loses the outline, so "Pour concrete" five times tells a reader nothing.
• Keep it shallow. Three levels under the project summary task is plenty for an owner's file. Depth belongs in the contractor's schedule.
• Milestones live in the element they finish. A separate "Milestones" block at the top breaks the 100% rule and makes milestones a second copy of the work. Use the built-in Milestones filter to list them.

Northgate worked example

The Northgate Distribution Centre (fictional) fact sheet fixes ten level 1 elements (see the fact sheet). The Owner's PM adds level 2 components in NDC_OwnerMaster_2027-01-11.mpp, on the calendar built in lesson 4. Table 1 shows the proposal. The milestones go where Figure 1 puts them.

The WBS code mask is three rows: Project Code Prefix NDC-; levels 1 to 3 as Numbers (ordered), Length Any, Separator period. Length Any matters, because a fixed length of 1 would refuse element 10. Codes then read NDC-3, NDC-3.3 and NDC-3.3.2. Figure 2 shows WBS 3 fully expanded.

Now suppose that in review the mechanical engineer argues that underslab services belong with mechanical and electrical work. The Owner's PM tries the move to see what it does to the codes (Figure 3), then puts it back: the underslab work is sequenced with the slab and must finish before M4, so it stays in WBS 3. The trade that does it can be shown with a resource or a custom field instead.

Screenshot to come

Screenshot to come

Owner's move

• Fix the owner's level 1 before the contractor's baseline. Halvorsen Builders Ltd. (fictional) owes its baseline schedule by Wed 2027-02-10. At the kickoff (M1, Tue 2027-01-19), the Owner's PM asks that every P6 activity carry the owner's WBS 1 to 10, as a WBS level or an activity code, so the two schedules can be rolled up the same way.
• Do not dictate the contractor's lower levels. The contractor may organize by area, trade or pour sequence. The owner needs a mapping, not a copy.
• Freeze codes at baseline. Renumber before baselining, then treat WBS codes as permanent. New scope gets the next code in its element; deleted scope leaves a gap.
• Report at level 1. Monthly owner reports use View > Outline > Level 1 plus the Milestones filter. If a board member asks about WBS 7, expand only that element.

Common mistakes

1. A WBS of phases or departments. "Design", "Procurement", "Construction" describe time, not deliverables, and make the 100% rule hard to check.
2. Linking or loading summary tasks. Links and resources on summaries make logic and resource checks unreliable.
3. A milestones block at the top. It duplicates work and drifts from the real tasks.
4. Fixed-length codes. A level 1 length of 1 cannot hold element 10.
5. Renumbering after the baseline. Every report, cost code and RFI that quoted an old code is now wrong.

Quick quiz

1. What happens when you indent a task in Microsoft Project?

   1. It is linked to the task above
   2. The task above becomes its summary task
   3. It becomes a milestone
   4. Its WBS code is deleted

2. Which statement about the Outline Number field is true?

   1. You type it like a WBS code
   2. It never changes
   3. Project calculates it from position, and it changes when tasks move
   4. It is only shown in P6

3. You move a task to another summary. What happens to its custom WBS code?

   1. It updates automatically
   2. It keeps its old code until you renumber
   3. It is cleared
   4. Project refuses the move

4. Why does the Northgate code mask use Length "Any" at level 1?

   1. To allow letters
   2. So element 10 is accepted
   3. To hide the prefix
   4. So codes renumber themselves

5. Where should the M4 milestone, Foundations and slab complete, sit in the Northgate outline?

   1. In a Milestones block at the top
   2. Under WBS 10 Closeout
   3. Under WBS 3, in 3.3 Slab-on-grade
   4. At level 0

Show answers and explanations

1. B. Indenting creates structure, not logic. Links are added separately.
2. C. Outline numbers are calculated and follow the task's position.
3. B. Microsoft notes WBS codes are not renumbered on a move or delete; use Project > WBS > Renumber.
4. B. A fixed length of 1 would reject a two-digit code.
5. C. Milestones live in the element whose work they complete, and the Milestones filter lists them all.

Key terms

Work breakdown structure (WBS)

A deliverable-oriented hierarchy that divides the project's total scope into manageable pieces.

100% rule

The WBS includes all of the scope and nothing else; children add up to exactly their parent.

Summary task

A task with subtasks indented under it; its dates, work and cost roll up from them.

Outline level

A task's depth in the outline: 0 for the project summary task, 1 for top-level tasks, and so on.

Outline number

A calculated number such as 3.1.2 that shows a task's position and changes when it moves.

WBS code

A task field that can follow a custom mask with a prefix and is not renumbered until you run Renumber.

References

1. Microsoft Support, Create and work with subtasks and summary tasks in Project desktop.
2. Microsoft Support, Create WBS codes in Project desktop.
3. Microsoft Support, WBS Code Definition dialog box.
4. Microsoft Support, Outline Number (task field) and Outline Level fields.
5. Microsoft Support, Keyboard shortcuts for Project.
6. PMI, What is a work breakdown structure (WBS)? (August 18, 2026).
7. PMI, Practice Standard for Work Breakdown Structures, Third Edition (2019).
8. BRC Academy, Lesson 4: Calendars and Ontario statutory holidays.

Verified on November 4, 2026.

Next lesson in this trackDurations and estimates