Work breakdown structure (WBS)

The WBS breaks a project into deliverables and work packages: plant, then area, then system, then package, in whatever logic suits the project. Its governing convention is the 100% rule — every level must contain all of the scope of the level above it, no more and no less — so that nothing in the project exists outside the structure.

Its value is that everyone hangs their data on the same tree. The schedule sequences WBS elements, the estimate prices them, progress is measured against them, and change is logged against them. When a scope item cannot be located in the WBS, that is usually the first visible symptom of scope that was never captured at all.

The common failures are structural: a WBS drawn by organisational department rather than by scope, so that work falling between departments has no home; or a structure defined after the estimate rather than before it, forcing a retrofit mapping that never quite closes.