project. An estimator 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.
Need for Accuracy
Quantity estimates are used as a basis for purchasing
materials, for determining equipment, and for
determining manpower requirements. They are also
used in scheduling material deliveries, equipment, and
manpower. Because of this widespread use, accuracy in
preparing quantity estimates is very important,
especially since an error in quantity tends to multiply
itself; for example, consider that a certain concrete slab
is to measure 100 feet by 800 feet. If the estimator
misreads the dimension for the 800-foot side as 300 feet,
the computed area of the slab will be 30,000 square feet,
when it should actually be 80,000 square feet. Since this
area will be the basis for ordering materials, there will
be a shortage of concrete ingredients, lumber,
reinforcing materials, and everything else involved in
mixing and pouring the concrete. This includes
equipment time, manpower, and man-hours.
Checking Estimates
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.
5-5
