A detailed estimate is one in which each component of a project scope definition is quantitatively surveyed and priced using the most realistic unit prices available.
Detailed estimates are typically prepared to support final budget authorization, contractor bid tenders, cost control during project execution, and change orders (Class 3 through Class 1 estimates). Detailed estimates use a deterministic estimating methodology and require a substantial amount of time and cost to prepare. It is not unusual for detailed estimates on
very large projects to take several weeks, if not months, to prepare and can require thousands of engineering hours to prepare the required technical deliverables.
The following is a description for detailed estimating activities associated with a process or
industrial project, but could easily be adopted for other types of construction-related projects, such as commercial construction. At a minimum, the required engineering and design data required to prepare a detailed estimate include process and utility flow drawings, piping and instrument diagrams, equipment data sheets, motor lists, electrical one-line diagrams, piping isometrics (for alloy and large diameter piping), equipment and piping layout drawings, plot plans, and engineering specifications. Pricing data should include vendor quotations, current pricing information from recent purchase orders, current labor rates, subcontract quotations, project schedule information (to determine escalation requirements), and the construction plan (to determine labor productivity and other adjustments).
prepare project estimate basis and schedule;
prepare direct field cost (DFC) estimate;
prepare indirect field cost (IFC) estimate;
prepare home office cost (HOC) estimate;
prepare sales tax/duty estimates;
prepare escalation estimates;
prepare project fee estimate (for contractors);
prepare cost risk analysis / contingency determination;
In a completely detailed estimate, all costs are detailed including the DFC, IFC, HOC costs, and all other miscellaneous costs for both the ISBL and OSBL facilities.
One variation of the detailed estimate is a semi-detailed estimate in which the costs for the ISBL process facilities are factored, and the costs for the OSBL facilities are detailed.
Another variation is the forced-detailed estimate in which detailed estimating methods are used with incomplete design information.
Typically in a forced-detailed estimate, detailed takeoff quantities are generated from preliminary drawings and design information.
The first step in preparing a detailed estimate is to begin establishing the project estimate basis and schedule. This is
essentially the pre-planning phase for the estimate. As mentioned, a detailed estimate for a large industrial facility may
take weeks to prepare, and involve several estimators and extensive support from engineering.
The estimate basis documents the activities and course of action that will be used to prepare the estimate. The first activity is to review the organization’s estimating guidelines and procedures with the estimating team.
The project work breakdown structure (WBS) should be reviewed with the project controls team, and agreement
should be reached on the estimate format, structure, and deliverables. The detailed estimate is typically used to support cost control during execution of the project and should be structured to accomplish that purpose.
The listing of engineering and technical deliverables to be used to prepare the estimate should be reviewed, and the procedures for receiving and tracking the drawings and other design information established. The estimating team should identify the estimating resources, techniques, and data that will be used during estimate preparation. Any estimate exclusions that are known at this time should be reviewed and documented.