Section 2: Individual LEED Credit Reviews
Summary of First Cost Impacts
existing site conditions; therefore the ratios of
hardscape and landscape are adjusted.
In the credit-compliant design scenario, the paved
Courthouse (New Construction, 262,000 GSF)
surfaces are reduced to 40 percent of the site area,
while the turf grass areas are reduced to 3 percent.
Increased Landscape Areas:
The areas of groundcovers and mixed, non-turf
vegetation are increased to 57 percent of the site
Total Credit Cost..................................... (5,055)
area. These adjustments result in a reduction in site
Cost Impact ($/GSF) ......................... (
||content||
.63)/GSF
imperviousness of 25.5 percent, as demonstrated in
Cost Impact (%) ........................................... (0.29)%
Table SS6.1-1 at the end of this section.
Since landscape irrigation is assumed in the Base
Vegetated Roof:
Case design, the irrigation system in the credit-
compliant design is expanded to cover the
Total Credit Cost........................................ 8,170
additional landscaped areas.
Cost Impact ($/GSF) ............................ .21/GSF
Cost Impact (%) ..............................................1.01%
Because this approach involves a significant
reduction in paved site area, it is not assumed to be
viable in all cases. It is only included in the three
"low cost" Courthouse scenarios.
The credit is not applicable.
Vegetated Roof
In this scenario, a 4-inch-deep (extensive)
Additional Considerations
vegetated roof covers 72 percent of the uppermost
roof of the Courthouse (65 percent of the overall
In some projects, the reductions in stormwater
roof area of the building). No changes are made to
runoff achieved through expanded landscape areas
the Base Case site development features. The
or vegetated roofs may result in lower costs for on-
addition of the vegetated roof results in a reduction
site stormwater collection and/or detention
in site imperviousness of 25.8 percent, as
systems (e.g., catch basins, piping, detention tanks).
demonstrated in Table SS6.1-2 at the end of this
section. Because the vegetated roof is only 4 inches
In some GSA projects (e.g., Courthouses), a
in total thickness (containing lightweight soils and
portion of the open site may be reserved for long-
only mosses and sedums as plant material), the
term building expansion. If expansion is known to
dead load does not increase enough to require
be likely at a given site, the stormwater runoff
upgrading of the roof structure (as compared to
reduction should be evaluated based on the
the Base Case ballasted EPDM roof system). As
expected post-expansion site/building areas.
the vegetated roof is based on an inverted roof
Synergistic Credits
assembly, it is assumed that the remaining areas of
the upper roof also employ the inverted system,
using ballast and pavers above the membrane and
Item SN-1 (Courthouse) of Section 3 reviews the
rigid insulation.
cost implications of earning credit SS-6.1
(Increased Landscape Areas option) in conjunction
Because of its expense, the vegetated roof
with credit SS-5.1 (Reduced Site Disturbance:
approach is only included in the "high cost" Gold
Protect or Restore Open Space) and credit WE-1.2
rating scenario for the Courthouse.
(Water-Efficient Landscaping: No Potable Use or
No Irrigation).
Item SN-2 (Courthouse) of Section 3 reviews the
cost implications of earning credit SS-6.1
(Vegetated Roof option) in conjunction with credit
SS-7.2 (Heat Island Effect: Roof) and credit EA-
2.1 (Renewable Energy).
GSA LEED COST STUDY
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