The 2,744 sq. ft. footprint of this two-story custom home
was used as the basis for the foundation cost comparisons
in Table 1, and for calculating
foundation + flood insurance costs in Table
3. The footprint includes the porches, but not the
garage.
A raised wood floor system is a cost-competitive alternative to a
concrete slab system, especially in areas where the builder must meet
a minimum "lowest floor elevation" at or above the Base Flood
Elevation (BFE) required by local floodplain management ordinances.
As shown in Table 1, the cost of building
a raised floor compares favorably to the cost of a slab. Table
1 summarizes the cost of just the foundation for four common
system types — two raised floor options and two slab options.
The spread between the four options is only $1,735, with the
cost of the elevated concrete slab option (at +1 BFE) the most
expensive at $14,751, and the monolithic concrete slab-on-grade
(at BFE) the least expensive at $13,016. The two raised wood
floor options (at +2 BFE) priced in between at $14,074 for the
pier-and-beam and $13,723 for the stem wall system.
In addition to cost-competitive construction for the builder
as shown, a raised floor can mean significant savings for homeowners
in flood-prone areas. Table
2 and Table 3
show how homeowners can realize dramatic reductions in annual
flood insurance premiums with a raised floor system. Furthermore,
the initial investment in a raised floor more than pays for
itself over a 30-year mortgage. For this example, the net result
for choosing a pier-and-beam raised wood floor at +2 BFE instead
of a concrete slab-on-grade (slab-on-ground) at BFE is an overall
savings of $6,605 for the homeowner as shown in Table
3. Savings begin immediately and grow larger during the
life of the mortgage as shown in Figure
1.
Table 1 Cost-Comparisons: Raised Floor vs.
Slab
RAISED FLOOR OPTION — PIER-AND-BEAM FOUNDATION
+ 2 BFE
Item
Amount
Material
Labor
Unit Cost
Cost
Excavation
Footings
10.9 CY
—
23.45
23.45
$
255
Termiticide
Soil Treatment
333 SF
0.24
0.21
0.45
$
150
Footings
Concrete
14.4 CY
92.00
39.78
131.78
$
1,899
#5 Rebar
296 LF
0.29
0.26
0.55
$
163
Foundation
CMUs
500 Units
1.68
2.61
4.29
$
2,145
#5 Rebar
222 LF
0.29
0.26
0.55
$
122
Concrete
2.7 CY
92.00
39.78
131.78
$
354
Beams
6x6 PT
346 LF
3.08
0.60
3.68
$
1,273
Band Joists
2x12 PT
216 LF
1.70
0.55
2.25
$
486
Joists
2x12 PT
1910 LF
1.70
0.55
2.25
$
4,298
Anchor Straps
1-1/4x20 ga.
62 Each
0.89
—
0.89
$
55
Porch
PT T&G Flooring
585 LF
0.41
0.20
0.61
$
359
Insulation
R-19 Fiberglass
1920 SF
0.35
0.10
0.45
$
864
Subfloor
19/32 Sturd-I-Floor
1920 SF
0.57
0.29
0.86
$
1,651
Total Estimated Cost for Raised
Floor Option — Pier-and-Beam
$
14,074
RAISED FLOOR OPTION — STEM WALL FOUNDATION +
2 BFE
Item
Amount
Material
Labor
Unit Cost
Cost
Excavation
Footings
10.9 CY
—
23.45
23.45
$
255
Termiticide
Soil Treatment
650 SF
0.24
0.21
0.45
$
293
Footings
Concrete
7.3 CY
92.00
39.78
131.78
$
961
#5 Rebar
442 LF
0.29
0.26
0.55
$
243
Foundation
CMUs
734 Units
1.68
2.61
4.29
$
3,150
#5 Rebar
311 LF
0.29
0.26
0.55
$
171
Concrete
1.8 CY
92.00
39.78
131.78
$
242
Beams
6x6 PT
125 LF
3.08
0.60
3.68
$
460
Band Joists
2x12 PT
216 LF
1.70
0.55
2.25
$
486
Joists
2x12 PT
1910 LF
1.70
0.55
2.25
$
4,298
Still Plates
2x8 PT
221 LF
1.03
0.22
1.25
$
276
Anchor Bolts
1/2x6"
50 Each
0.28
—
0.28
$
14
Porch
PT T&G Flooring
585 LF
0.41
0.20
0.61
$
359
Insulation
R-19 Fiberglass
1920 SF
0.35
0.10
0.45
$
864
Subfloor
19/32 Sturd-I-Floor
1920 SF
0.57
0.29
0.86
$
1,651
Total Estimated Cost for Raised Floor Option —
Stem Wall
Total Estimated Cost for Slab Option — Monolithic
on Grade
$
13,016
Source: Estimate prepared by Thomas
Stevens, III, Florida Certified Building Contractor, St. Pete
Beach, Florida, using MEANS cost data, January 2003. Based on
a 2,744 sq. ft. foundation footprint for a two-story house required
to meet the strict Florida Building Code.
BFE = base flood elevation CY = cubic yards
SF = square feet LF =
lineal feet CMUs = concrete masonry units
PT = pressure treated
T&G = tongue & groove
