Levels of Estimating

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As a construction project is conceived and developed its cost estimation and information may change as per the requirement of the designer, owner or client. Various factors are assumed at the beginning of a project which are gradually eliminated as the pricing of the quantities are more clear and detailed. At each level of design process of the construction, estimates have to be prepared based on the increasing degrees of information provided. At each level of estimation, not all the portion of the design is at the same level of completion. Like, if the mechanical design is 80% complete, the architectural design will only be 50% complete. This should be included in the estimate narrative.

Estimates for process or manufacturing areas require information about construction costs, process layout, flow diagrams, service requirements, product line capacity, handling requirements, utility requirements, materials & storage required and raw materials access. Estimates within each of the levels are prepared and modified several time during the designing Procedure. The different levels of construction cost estimate include -

• Order of Magnitude - Here the budgetary and feasibility determinations are provided. Based on past information, a project budget is prepared to meet its conditions. The estimation is determined on the basis of costs per square foot, number of rooms etc. General functional description, geographic location, schematic layout, size provided as per building area, number of people, building use etc are included as project information for the estimate.

• Schematic/Conceptual Design - At this level comprehensive cost estimation is prepared to compare with the budgetary and feasibility determinations made in the previous level. It is based on an improved version of the scope of work, a detailed building program, diagrams, conceptual plans, schematic drawings, sketches, renderings, elevations, sections and preliminary specifications. This estimation is employed to rate different design schemes to trace which scheme suit the budget. It is also used to price different construction materials, design alternatives and methods for comparison. The schematic design includes program, design scheme and estimate that can be incorporated in the budget. Information is provided on all the factors that may have an impact on the estimation of construction cost. This includes description of the geotechnical conditions, soil, foundation and utility requirements, construction type and size determinations.

• Design Development - Estimates prepared under design development verifies the budget conformance since at this level the scope and design are finalized and the selection of the materials are selected. 25% of the complete drawings of floor plans, sections, elevations, typical details, system single line diagrams, engineering design criteria, preliminary schedules like finishes, partitions, doors, and hardware, typical details, equipment layouts and outline specifications are required to create information at this level. This level is more precise with well defined and detail design documentation. Before the completion of specifications and design drawing, estimation at this level is used for engineering applications.

• Construction Documents - The estimation drafted in this level is on the basis of construction documents are about 90% complete. It is used to verify the construction cost as the design is on the verge of completion. It also confirms the funding allocations and helps in assessing the potential value engineering opportunities before the publication of the complete project design documentation for bids. In this level one can identify any kind of "design creep" items and their altered price due to the changes during the completion of the construction documents. To evaluate the subcontract pricing during the bid phase, this construction document cost estimate is employed.

• Bid Phase - In an usual design- bid- build delivery process all the documents are well co-ordinated and 100% complete. This is the final level a probable cost is estimated to prepare and submit bids for contract with the owner and is used to evaluate sub-contractor bids and modify orders during the construction. With other delivery systems like guaranteed maximum price and design- build, the bid is prepared at design development level where the design is only 25% complete or at construction documents level with 90% of the documents is complete. In such a case it is important to include complete and detail statement of the documents used for the estimate, contingency amounts included, items assumptions, allowances etc.