Estimating semi-detailed

General Order of Magnitude and Conceptual Estimates Semi-Detailed Estimate... 

Design estimate (budget authorisation estimate or scope estimate) based on a semi-detailed analysis. This approach incorporates a mixture of different methods with probable accuracy within +15/20%. 

The semi-detailed estimating system and related procedures presented in this book will allow project managers to prepare reasonably accurate estimates very quickly and confirm the validity of estimates prepared by others even quicker. 

Once the basic execution decisions have been reached, the long deliveries determined, the MPS prepared, and the appropriation estimate completed, the firm execution plan can be prepared. The plan must include sufficient execution details and schedule information to become the baseline for an in-house progress monitoring system. Such a plan can be prepared with a reasonable effort from the information contained in a Phase 1 design package and a preliminary semi-detailed cost estimate like the one in Appendix L. 

THE SEMI-DETAILED ESTIMATING TECHNIQUE PROPOSED IN CHAPTER 19 PROVIDES THE OWNER S PROJECT MANAGERS WITH A SIMPLE WAY TO PREPARE QUALITY ESTIMATES WITHOUT RESORTING TO CONTRACTORS OR TO COMPLICATED TECHNIQUES. 

While a detailed estimate could not be prepared without the benefit of some detailed engineering, a good semi-detailed estimate can be prepared with the information available at the completion of the Phase 1 design. 

The quality of a semi-detailed estimate will, of course, be enhanced if it is prepared at the completion of the basic engineering. 

As discussed in Section 10.4, the breakdown of cost items (take-offs) can go down to the level of nuts and bolts (detailed) or be based on larger, more comprehensive units (semi-detailed). Both approaches are valid provided that the scope of the unit prices corresponds to the units and that adequate resolution allowances are included to compensate for omissions and oversights. The estimate review must address the breakdown philosophy to ascertain that the unit prices and resolution allowance are consistent with the details of the take-offs. 

The Project Manager and the Contract Engineer must have a good understanding of the scope and the cost of the work in order to evaluate bidders and analyze the bids. To do so, they need a good cost estimate with detailed or semi-detailed takeoffs. 

A semi-detailed cost estimate prepared with the procedures and guidelines included in Chapter 19 could easily be dissected into a multitude of comprehensible construction activities that could be integrated, at the Project Manager s option, into a manageable number of discretely sized units. Every single activity could be assigned consistent relative values based on field hours... 

The proposed semi-detailed estimating system is consistent with the guidelines presented in Section 10.4 and includes simple procedures and tools that will allow project managers to quickly and accurately ... 

Prepare, when necessary, semi-detailed estimates (for small projects) suitable for appropriation and/or further project control. 

A semi-detailed estimate could be conceptual, preliminary, or definitive, depending on the quality of the information provided. In any case, the following information is required ... 

The preparation of a semi-detailed estimate for a medium sized chemical plant with 50 to 100 pieces of equipment should take 5 to 7 working days, including 3-4 days to develop preliminary equipment arrangements and doing all calculations manually. The various accounts are estimated as follows ... 

Note For a preliminary estimate, the cost can be calculated in a few minutes with the aid of the charts provided. For definitive estimates intended for appropriation and/or progress monitoring, the cost should be developed with the semi-detailed procedure. Both approaches should result in approximately the same cost. 

Figure 19.1 summarizes the scope and applications of the proposed semi-detailed estimating system. 

These procedures are more suitable for detailed or semi-detailed estimates where the various commodities (civil, piping, electrical, etc.) are estimated individually or related to equipment count rather than to equipment cost. These procedures should not be used in factored estimates where an error in the equipment account would be greatly amplified by the time it reaches the bottom line. 

Semi-Detailed Estimating System Table 19.1 (Continued)... 

Tables 19.20 through 19.23 can be used either for semi-detailed or detailed estimating of piping and equipment, hot and cold insulation.

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