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21–1 Overview
For the most of this book, we have focused on the detailed
estimate, identifying and pricing each of the components
needed to build a project. Other estimating methods were
introduced in Chapter 1. In this chapter, we will look at
project comparison, square foot, and assembly estimating
methods in more depth. Care must be taken when using
these methods because they often produce less accurate
results than a detailed estimate, but results that are accu-
rate enough for the purpose of some estimates. The esti-
mator should make sure that the estimating method used
is appropriate for the purpose of the estimate. When
ordering materials, there is no substitute for a good
detailed estimate.
21–2 Project Comparison Method
A project comparison estimate is prepared by comparing
the proposed project to one or more similar projects that
the company has built. The estimator starts with the costs
for a similar project and then adjusts these costs for any
differences between the comparison project and the pro-
posed project. When comparing the project to multiple
projects, the cost of the proposed project should be calcu-
lated for each comparison project, and then the estimator
uses his best judgment as to which of the costs is most
accurate.
When preparing a project comparison estimate, the
estimator must make sure that the projects are very similar
in both design and use. It is obvious that one cannot use
the costs from a warehouse to determine the costs of a
school. They are simply too different. But what about using
the costs for an apartment complex to estimate the costs
for a condominium project? Even if the design is the same,
the use and clientele are different. It costs more to deal with
many owners (in the case of the condominiums) rather
than one owner (in the case of the apartments). If this
comparison is made, the estimator needs to take into
account the difference in the use and ownership. When
comparing two projects, the estimator needs to consider
the following:
Size. The size (usually square footage) should be
within 10 percent for the projects being compared. As
the size of the building increases, the cost per square
foot decreases. Conversely, as the size decreases, the
cost per square foot increases. This is due to economies
of scale.
Height between floors. Increasing the height between
floors increases the envelope cost without increasing the
square footage of the building.
Length of perimeter. Two buildings, a long skinny one
and a square one, will have very different perimeters and
envelope costs for the same square footage.
Project location. Labor availability, materials availability,
and government regulations vary by location.
When the project was built. Inflation in labor, materials,
and fuel costs; weather (summer versus winter).
Type of structure: Concrete, steel, wood framed, block.
Level of finishes. Quality of materials and workmanship.
Utilization of the space. Some spaces cost more than
others do. Bathrooms and kitchens cost more per square
foot than bedrooms.
Union versus nonunion labor.
Soil conditions.EXAMPLE 21-1 PROJECT COMPARISON
Last year your construction company built a 70,000-sf warehouse
for $6,203,595. The owner wants to build another warehouse of
similar size; this time they want to add 1,000 sf of office space in
one corner of the building. It is estimated that the offices space will
cost $100,000 and that costs have risen 3 percent during the lastOTHER ESTIMATING METHODS
CHAPTERTWENTY-ONE