Estimating in Building Construction

year. Using this information, prepare a preliminary estimate for the
new warehouse.



When collecting data for use in project comparison, it
is important that any unusual conditions that would skew
the costs higher or lower be documented. It is simply not
enough to record just the cost. The estimator must know
whether the cost is typical for the type of project and under-
stand why the cost might have been higher or lower than the
average.

21–3 Square-Foot Estimating

Square-foot estimates are prepared by multiplying the
square footage of a building by a cost per square foot and
then by adjusting the price to compensate for differences in
the design. Units other than square footage may be used;
for example, a parking garage may be measured by the
number of parking stalls. The cost per square foot or other
unit may be determined by dividing the cost by the size of
the building.

EXAMPLE 21-2 SQUARE-FOOT ESTIMATE

Last year your construction company built a 100,000-sf, 5-story
parking garage for $5,395,621. The parking garage included one

$6,489,703 — Use $6,490,000

Cost ($)$6,203,5951 .03$100,000

Other Estimating Methods 227

elevator, which cost $126,345, and its costs are included in the

$5,395,621. Using this information, prepare a preliminary cost

estimate for a 95,000-sf, 5-story parking garage with two eleva-

tors. It is estimated that costs have risen 3 percent during the last

year.

Determine the cost per sf for the parking garage, excluding the

elevator.

Add costs and adjust for inflation.



The square-foot method may be used for the entire pro-

ject of just specific trades within the project. For example, we

may prepare a square-foot estimate for the electrical to check

our electrical pricing. In addition, the square-foot method

may be applied to each cost code in a bid. This requires the

estimator to think through each cost code and determine the

best unit of measure to use each cost code. Some items may

be best based on the square footage (for example, floor slabs

and roofing) or the length of the perimeter of the building

(for example, exterior brick), and others may be nearly fixed

for a building unless a large change in size occurs (for exam-

ple, elevators).

$5,415,987—Use $5,420,000

Total cost ($)$5,258,2401 .03

Total cost ($)($5,005,550$252,690)1.03

Add for elevators ($)$126,345 2 $252,690

$5,005,550

Cost without elevators ($)$52 .69 per sf95,000 sf

$52.69 per sf

Cost per sf ($>sf)($5,395,621$126,345)>100,000 sf

EXAMPLE 21-3 LINE-BY-LINE SQUARE-FOOT ESTIMATE

Last year your construction company built a 3-story, 26,000-sf
apartment building for $1,915,071. The costs by cost code are
shown in the second column of Figure 21.1. The perimeter of the
building was 240. Using this information, prepare an estimate for a
3-story, 24,000-sf apartment building with a perimeter of 200.The
apartments have the same room counts, kitchen sizes, and bath-
room sizes.
Use the square-foot method to adjust each line of the cost
codes. The cost codes will be adjusted based upon the ratios of the
areas, the ratio of the perimeters, or will be treated as a fixed cost.
The ratio of the areas is determined by dividing the new area by the
old area. Multiplying the total cost of the old project by the area
ratio is equivalent to dividing the total cost of the old project by the
old area to determine a cost per square foot for the old project and
then multiplying the cost per square foot by the new area. This
results in an estimated cost for the new building. The ratios for this
building are as follows:

Items that change proportionally with the area of the building will
be adjusted using the area ratio. The following will be adjusted
using the area ratio: under-slab gravel, slab floor, light-weight

Perimeter Ratio 200 ¿> 240 ¿0 .833

Area Ratio24,000 sf>26,000 sf0 .923

concrete, rough carpentry, lumber, trusses, finish carpentry,

insulation, roofing, drywall, carpet and vinyl, paint, and wire

shelving.

Items that deal with the exterior wall of the building will be

adjusted using the perimeter ratio. The following will be adjusted

using the perimeter ratio: footing and foundation, rebar, masonry,

waterproofing, stucco, siding, and rain gutters.

Some items are a function of the number of rooms and the

size of the kitchens and bathrooms. For example, a small

increase in the square footage, without changing the number of

rooms, will have little effect on the heating system other than

adding or subtracting a few feet of duct; the door count would

remain the same. Because the number of rooms and the size of

the kitchen and bathrooms are the same, these items are treated

as fixed costs and will not be adjusted. These items include mis-

cellaneous steel, firesafing, metal doors and frames, wood doors,

hardware, windows, window sills, appliances, cabinetry and

counter tops, window treatments, plumbing, HVAC, electrical,

and clean-up.

The adjustment factor is shown in the third column of

Figure 21.1, and the adjusted cost estimate for the new apartment

building is shown in the fourth column. From Figure 21.1, we see that

the cost per square foot increased by $1.54 (2.1%) due to changes in

the size of the building and length of the perimeter.