Section 2: Individual LEED Credit Reviews
Supporting Calculations
Imperviousness calculations are included in Table
SS6.1-1 and Table SS6.1-2.
Table SS6.1-1: Landscape Revisions to Achieve 25% Stormwater Runoff Reduction
Total Lot Area (SF):
133,423
Non-Building Site Area (SF):
86,450
Design Case Table
% of Non-
Area
Runoff
Impervious
#
Surface Type
% of Total Lot
Building Site
(SF)
Area (SF)
Coefficient
Courthouse Building:
3,700
0.95
3,515
1
Lower Roof
2.8%
n/a
Upper Roof
32.4%
n/a
43,273
0.95
41,109
2
Building Total
35.2%
--
46,973
--
44,624
Paving:
3
Vehicle access paving
3.2%
5.0%
4,323
0.95
4,106
Sidewalk paving and curb
10.4%
16.0%
13,832
0.95
13,140
4
5
Plaza paving
10.4%
16.0%
13,832
0.95
13,140
6
Steps and landings
1.3%
2.0%
1,729
0.95
1,643
Paving Total
25.3%
39.0%
33,716
--
32,030
Water Feature:
7
Pool/fountain
0.6%
1.0%
865
0.95
821
Water Feature Total
0.6%
1.0%
865
--
821
Street Trees:
Street Trees (3" caliper)
0.6%
1.0%
865
0.35
303
8
9
Street Trees (2" caliper)
0.6%
1.0%
865
0.35
303
Trees Total
1.3%
2.0%
1,729
--
605
Mixed Vegetation:
10
Shrubs/Trees in Barrier Garden
14.6%
22.5%
19,451
0.20
3,890
11
Shrubs and Perennials
3.2%
5.0%
4,323
0.20
865
23,774
--
4,755
Mixed Total
17.8%
27.5%
Groundcover only:
12
Groundcover mix
17.8%
27.5%
23,774
0.20
4,755
Groundcover Total
17.8%
27.5%
23,774
--
4,755
Turfgrass:
13
Turf areas
1.9%
3.0%
2,594
0.35
908
Turfgrass Total
1.9%
3.0%
2,594
--
908
133,423
Total Area:
Total Impervious Area:
88,498
Imperviousness:
66.3%
Baseline Case Table
% of Non-
Area
Runoff
Impervious
#
Surface Type
% of Total Lot
Building Site
(SF)
Coefficient
Area (SF)
Buildings and Site Paving:
Existing building roofs and site
1
90%
--
120,081
0.95
114,077
paving surfaces
Impervious Area Total
90%
120,081
114,077
Landscape:
2
Existing site plantings
10%
n/a
13,342
0.35
4,670
Landscape Area Total
10%
13,342
4,670
Total Area:
133,423
Total Impervious Area:
118,746
Imperviousness:
89.0%
Imperviousness decrease is:
25.5%
GSA LEED COST STUDY
43
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