A material estimate is a listing and description of the various materials required to construct a givenestimator is one who evaluates the requirements of a construction task and determines the quantities of materials needed to accomplish that task As an EA2, you maybe called upon to assist in preparing material estimates, especially for bulk materials, such as fill materials, concrete, and asphaltic paving materials. To be a good estimator, you must have sound and thorough construction knowledge and experience, and you must be familiar with the techniques and pitfalls of material estimating. It is beyond the scope of this book to give you the construction knowledge and experience you will need; however, this section does introduce you to some of the techniques and pitfalls that you will use or encounter when estimating material requirements.

USE OF DRAWINGS AND SPECIFICATIONS

Construction drawings are the main basis for defining required construction activities and for measuring quantities of material. Accurate estimating requires a thorough examination of the drawings. All notes and References should be read carefully, and all details and reference drawings should be examined. The orientation of sectional views should be checked carefully. Dimensions shown on drawings or computed figures shown from those drawings should be used in preference to those obtained by scaling distances. An overall dimension shown on a drawing should be checked to see if it tallies with the sum of the partial lengths. If scaling is unavoidable, the graphic scale must be checked for possible expansion or shrinkage at a rate different from that of other parts of the drawing. The revision block should be checked for changes made to the drawings. The construction plan, the specification, and the drawing must be verified to see if they are, in fact, all talking about the same project. When there are inconsistencies between general drawings and details, details should be followed unless they are obviously wrong. When there are inconsistencies between drawings and specifications, the specifications should be followed.

The estimator must first study the specifications and then use them with the drawings when preparing quantity estimates. The estimator should become thoroughly familiar with all the requirements stated in the specifications. Most estimators will have to read the specifications more than once to fix these requirements in their minds. If the estimator makes notes while reading the specifications, these notes will prove helpful when the drawings are examined. In the notes, the estimator should list items of work or materials that are unusual or unfamilar. These notes should also contain reminders for use during examination of the drawings. A list of activities and materials that are described or mentioned in the specifications will be helpful in checking quantity estimates.

The Seabee Planner's and Estimator Handbook, NAVFAC P-405, is a publication that has been prepared specifically for the Seabee estimator. Whenever possible, the tables and the diagrams contained in the P-405 are based on the Seabees experience. Where suitable information was not available, construction experience was adjusted to represent production under the range of conditions encountered in Seabee construction. Using the P-405 will save you time in preparing estimates and, when understood and used properly, will give accurate results.

Quantity estimates should be checked in a manner that will eliminate as many errors as possible. One of the best ways to check your quantity estimate is to have another person make an independent estimate and then to compare the two estimates after both are completed. Any differences should be checked to see which estimate is right. A less effective way of checking is for another person to take your quantity estimate and check all measurements, recordings, computations, extensions, and copy work.

Figure 5-2.Foundation plan and detail.

Sources of Error Failure to read all the notes on a drawing or failure to examine reference drawings results in many omissions; for example, an estimator may overlook a note that states "symmetrical about ~ and thus compute only half of the required quantity. Errors in scaling obviously mean erroneous quantities. Great care should be taken in scaling drawings so that correct measurements are recorded Some common scaling errors are using the wrong scale and failing to note that a detail being scaled is drawn to a scale different from that of the rest of the drawing. Remember that some drawings are not drawn to scale. These, of course, cannot be scaled for dimensions. Sometimes a wrong interpretation of a section of the specifications can cause errors in the estimate. If the estimator has any doubt concerning the meaning of any portion of the specification, he should request an explanation of that portion.

Construction materials are subject to waste and loss through handling, cutting to fit, theft, normal breakage, and storage loss. Failure to make proper allowance for waste and loss results in erroneous estimates. Other sources of error are copying errors, inadvertent figure transpositions, and computational and arithmetic errors.