Direct and indirect costs

Construction cost is split into direct and indirect costs because they behave differently and are controlled differently. Direct costs are those that can be traced to a specific item of permanent work: the cement, steel, aggregate and labour in a column, the hire of the excavator digging a trench, the subcontract for waterproofing. They are estimated from quantities multiplied by unit rates.

Indirect costs support the work as a whole but cannot be tied to one item. Site overheads, sometimes called preliminaries or general conditions, include site staff and supervision, temporary offices, stores, fencing and security, site power and water, safety measures, testing laboratories, insurance, bank guarantees and permits. Many of these are time-related: they accrue every day the site is open, so delays raise them directly. Others are fixed, like mobilisation, or value-related, like insurance premiums. Head office overheads cover the contractor's corporate costs and are recovered as a percentage. Profit is added on top, along with a contingency for risk.

The distinction matters in tendering, where indirect costs may be priced as separate items or spread into unit rates; in time-cost trade-off analysis, where shortening the project reduces time-related indirects; and in claims for delay, where prolongation costs are mainly indirect. Good cost reporting keeps the two separate so that management can see whether overruns come from productivity on the work itself or from the project taking longer.