If funding is limited (which it usually is!), the owner will desire an estimate of the final cost beginning early in the project’s life. Of course, until final construction contracts are arranged, this estimate can only be an approximation. The cost estimator is responsible for compiling this information. As we shall see in Chapter 4, cost estimates can be prepared at various levels of detail. In the planning stage, little information is available about the physical properties of the project elements and thus the estimate of cost has little detail. As more design is developed, the cost estimator provides more detailed cost numbers.
The degree of accuracy improves as more detail is developed. Early in the planning process, when little more than the total project area is known (and that perhaps only preliminarily), the cost estimate is probably accurate to within ±30%. Part-way through the design process, cost estimates ought to be accurate to within ±20%; when final construction documents are ready for the tender process, an estimate of accuracy of ±10% can be expected. Although we imply that the cost estimator is a separate member of the team, often the architectural or engineering designer performs this task in association with the various design activities; the term engineer’s estimate is often used for that estimate prepared at the completion of design development.