Resource Breakdown Structure (RBS)

The Resource Breakdown Structure (RBS) catalogues all the resource types a project will use, organised hierarchically. The top level might distinguish between labour, plant, and materials. Below that, labour is broken into disciplines (civil engineers, electricians, project managers), plant into types (excavators, cranes, concrete pumps), and materials into categories (steel, concrete, cable). The RBS is used to structure resource planning, to support cost estimation (because resource types map to cost rates), and to provide the framework for resource loading in the schedule.

The RBS works in conjunction with the WBS and CBS to create a three-dimensional view of the project: what is being built (WBS), what it costs (CBS), and what resources are needed to build it (RBS). In resource-loaded scheduling tools such as Primavera P6, resources are assigned to schedule activities using the RBS categories, which allows the schedule to calculate resource demand profiles over time — the basis for resource levelling and smoothing. In cost models, resource quantities and rates from the RBS are the building blocks of the bottom-up estimate.

On smaller projects, the RBS is often implicit rather than formally documented — the project team just knows what kinds of resources they have and plans accordingly. On major programmes, a formal RBS is essential for consistent resource coding across multiple packages and contractors, for workforce planning, and for tracking actual resource utilisation against plan. The RBS also underpins the risk analysis: when modelling the impact of a shortage of specialist resources (a common risk on infrastructure programmes), the risk needs to be linked to the specific RBS element that defines the scarce resource type, so that the schedule and cost model correctly propagates the impact across all the activities that depend on that resource.