Item-based costing involves tracking each work item (position) in a construction project separately, with its own quantity, unit price, and actual expenditure. The Work Breakdown Structure (WBS) is the framework that divides the project into hierarchical parts at the site, activity, and item levels. The two work together: the WBS shows "which phases" the project is divided into, and the item-based costing shows "how much" is spent in those phases. Without this duality, budget deviations would only become apparent after the work is completed.
An item is the smallest work item defined in the bill of quantities and survey, with its own unit price — such as "1st floor wall plastering", "B block foundation concrete". Item-based costing means seeing the total project budget not as a single figure, but as the planned and actual amount for each item. In practice, this means that even if the total budget appears to be balanced in a project, one item might be exceeding it by 40%, and another item might not even have started yet. The total figure hides this imbalance. Item-based tracking shows exactly which work item, which construction site, and on what date the deviation occurred. In Unit Price Bid (UPB) contracts, this is already the basis of progress payments; in Lump Sum Turnkey (LUM) contracts, the same logic is applied for internal cost control, even if it is not reflected in the progress payment.
WBS is a hierarchical structure that breaks down a project into manageable parts. In construction, three to four levels are typically used:
In a properly configured WBS, each position is linked to exactly one activity, and each activity to exactly one location — there are no conflicts or gaps. In Business Central's Projects module, this structure is established with job tasks; each task corresponds to a WBS node, and each task row corresponds to a cost.
These two concepts are often confused, but they serve different purposes. A Work Structure (WBS) defines the breakdown logic of a project—the levels at which reporting will be done. A "item" (or "position") is the actual carrier of cost —a work item defined in the cost estimate, with a unit price. In practice, an item is the lowest level of the WBS structure. For example, under the "Block A → Rough Construction → Concrete Works" branch, there would be items like "C30 foundation concrete" and "C25 slab concrete." As construction progresses, the actual cost recorded for these items is automatically consolidated to the activity above, the location, and finally the project total. While skipping the item level and budgeting directly on an activity basis might seem like less data entry in the short term when structuring the WBS, it makes the source of the discrepancy invisible—you only notice the problem after construction has progressed significantly.
A project cost center is a classification that determines which project, site, and node in the WBS a cost belongs to. Without distributing expense and revenue records in accounting to these centers, you obtain a single total figure, not a position-based table. Cost center differentiation is particularly critical in multi-site companies: records from multiple sites are transfer