Page 105 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

86 Cha pte r T w o

Note that for either type of roofed surfaces, it is not the sum of the areas with the minimum
SRI, but rather a sum of areas whose areal weighted average SRI meets the minimum
criteria. For example, for two steep-sloped roof areas, each of equal area, one with an SRI of
28 and the other with an SRI of 30, both areas could be counted with an average SRI of 29.
Using these definitions, the project would be eligible for this credit if the following
inequality held true.

TR ≤ RRL + RRS + VR (2.7.4)
.
.
075 05
The first half of the right side of Eq. (2.7.3) corresponds to the requirements of Option 1,
and the second part of the right side of Eq. (2.7.3) corresponds to the requirements for
Option 2.

Special Circumstances and Exemplary Performance
There are some special cases for which it is difficult to determine if a hard surface is a
roof or non-roof or considered neither. One example is open stadium seating. These
special exceptions should be reviewed through the USGBC CIR procedure. If there are
other special circumstances or considerations for this credit, a narrative must be
submitted describing these circumstances.
An EP point may be awarded if it can be demonstrated that Option 2 is met with a
100 percent vegetated requirement. This means that all the roof areas excluding mechanical
equipment, solar panels, skylights, and other similar appurtenances comprise green
(vegetated) roof systems.

VR = TR (2.7.5)

A summary of the criteria equations for SSc7.2 is given in Table 2.7.4.
Many websites are being developed that give alternatives for green roofs. In
addition, ASTM International is developing an international standard, WK14283,
“Guide for Green Roof Systems,” which will aid in understanding concepts and
terminology in green roof design. Figure 2.7.3 shows the front of a building which has

Criteria for Option 1 Option 2 Option 3
Credit Given TR = BF − EQR, Given TR = BF − EQR, Given TR = BF − EQR,
point
RRL + RRS VR RRL + RRS VR
TR ≤ TR ≤ TR ≤ +
.
.
.
.
075 05 075 05
(At least 75% of (At least one-half of (Combination of Options
roofed areas meet the roofed areas are 1 and 2)
set SRI criteria.) vegetated.)
EP point n/a Given TR = BF − EQR, n/a
VR = TR
(All roofs are vegetated.)
TABLE 2.7.4 Summary Criteria Equations for Heat Island Effect: Roof LEED 2009