Work breakdown structure

A WBS starts with the whole project at the top and breaks it down level by level. A typical commercial building might split first by stage or building, then by level or zone, then by trade package or element, such as substructure, structure, facade, services and fit-out.

The lowest level is the work package: a piece of work small enough to be estimated, programmed, assigned to one responsible party and checked as complete. Programme activities and cost codes then hang off those work packages.

The WBS describes what is being delivered, not when. The sequence and durations come later, when the planner turns work packages into programme activities and links them together.

• Full scope coverage. Every part of the contract scope sits somewhere in the WBS, including preliminaries, design, approvals and handover, not just the physical works.

• No overlaps. Each piece of work sits in one place only, so it cannot be costed or programmed twice.

• A consistent logic at each level. Mixing zones and trades on the same level makes reporting confusing. Pick one breakdown per level and stick to it.

• A clear numbering system. Codes such as 2.3.4 let the programme, budget and cost reports link back to the same item.

• Clear ownership. Each work package has one responsible person or subcontractor.

People often use the terms interchangeably, but they do different jobs. The WBS is the structure: a list of everything to be delivered, grouped logically. The construction programme is the schedule: activities with durations, dependencies and dates.

A well-built programme uses the WBS as its outline, so activities are grouped under the same headings the cost plan uses. That is what lets a project team compare progress and cost on the same item, and it makes it much easier to explain the impact of a delay or variation on a specific part of the job.

The WBS also links to the cost breakdown structure. On many projects the cost codes are simply the WBS codes with cost types added, such as labour, materials, plant and subcontract.

The same structure is useful for subcontract packaging. When work packages line up with how the job will be let, each subcontract maps cleanly to a set of WBS codes, which makes commitments, progress claims and cost to complete reporting far simpler.

• Breaking it down too far. Hundreds of tiny packages create admin without better control. Stop at the level you will actually manage and report on.

• Building it around the organisation chart. A WBS should follow the deliverables, not who reports to whom.

• Leaving out non-physical work. Design, authority approvals, commissioning and handover documents take time and money too.

• Creating separate structures for time and cost. If the programme and budget use different breakdowns, the team will spend every month reconciling them by hand.