Section 2: Individual LEED Credit Reviews
LEED Credit SS-7.2:
A vegetated roofing system might also be
considered in some projects, particularly in
Heat Island Reduction
situations where stormwater management is a
concern, or in cases where the green roof provides
Roof
an additional building function (e.g., exterior
programmed space).
Intent:
Basis for Cost Assumption
Reduce heat islands (Thermal gradient
The Base Case model for the Courthouse assumes
differences between developed and undeveloped
the use of a ballasted EPDM roof system. Two
areas) to minimize the impact on microclimate
approaches were estimated to meet the credit
and human and wildlife habitat.
criteria, as described below.
Requirements:
ENERGY STAR Roof
Use ENERGY STAR compliant (high reflective)
The EPDM roof is replaced by a white
AND low emissivity roofing (emissivity of at
thermoplastic polyolefin (TPO) roof membrane
least 0.9 when tested in accordance with ASTM
system, direct glue-down. There was no cost
408) for a minimum of 75% of the roof surface;
increase identified with this system change.
OR
Vegetated Roof
Install a "green" (vegetated) roof for at least
A 4-inch-deep (extensive) vegetated roof system
50% of the roof area. Combinations of the high
covers 55 percent of the uppermost roof of the
albedo and vegetated roof can be used providing
Courthouse (50 percent of the overall roof area of
they collectively cover 75% of the roof area.
the building). Because the vegetated roof is only 4
inches in total thickness (containing lightweight
(1 point)
soils and only mosses and sedums as plant
material), the dead load does not increase enough
to require upgrading of the roof structure (as
Cost Impact = 2 or 5
compared to the Base Case ballasted roof system).
As the vegetated roof is based on an inverted roof
assembly, it is assumed that the remaining areas of
1
2
3
4
5
the upper roof also employ the inverted system,
GSA
No
Low
Moderate
High
using ballast and pavers above the membrane and
Mandate
premium,
premium
premium
premium
rigid insulation.
(no cost)
psble svgs
(<50K)
(50-150K)
(>150K)
Because of its expense, the vegetated roof
Practical Applications
approach is only included in the "high cost" Gold
rating scenario for the Courthouse.
The most direct strategy for meeting this credit is
As roofing replacement is categorized as an
to install a white or light-colored roof membrane
ongoing maintenance expense for GSA buildings,
system. Typical systems include the following:
it is not typically included in the scope of an Office
Building modernization. The credit is therefore not
White TPO
included in any of the Office Building scenarios.
White PVC
White EPDM
GSA LEED COST STUDY
49
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