Page 99 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

80 Cha pte r T w o

areas associated with parking areas), walks, roads, patios, and drives. Even water
features are included in the hardscape if they are contained over impervious surfaces
which can be exposed when dry. HS is defined as the sum of these non-roof hardscape
areas. 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.
It is very important to understand the criteria for each of the three pathways to do
this. They are shaded, high SRI, or open grid pavement systems.

• Shading. Shading can be effected with vegetation, or if tree planting is not
available, then architectural shading devices may be substituted, and LEED
2009 requires that these are either covered with solar panels or have an SRI of at
least 29. Roofed areas do not count in the hardscape calculation. The vegetation
used must be native or adaptive trees, large shrubs, and noninvasive vines (on
trellises or other supportive structures as needed). Deciduous trees are many
times preferred, especially in northern climates, as they allow for benefits from
solar heating of the pavement in the winter months when their leaves are gone,
such as reduced icing. Variable S is defined as the effective area of the hardscape
that is shaded. It is the arithmetic mean of shade coverage as calculated at 10
a.m., noon, and 3 p.m. on the summer solstice. Although not stated in LEED-
NC 2.2 or 2009, the time is probably what is accepted as the local time (daylight
or standard) at the location.
• SRI. Variable R is defined as the area of the hardscape that has an SRI of at least 29.
The definition of the SRI can be found in App. B. It represents a combination of
high reflectance and high emissivity. Both emittance and reflectance should be
calculated or determined according to the appropriate ASTM (American Society
for Testing and Materials) standard as listed in the definition. These values can
then be inserted into the LEED submittal template worksheet, and the appropriate
SRI will be calculated. Some typical SRI values as given in LEED-NC 2.2 and
2009 are listed in Table 2.7.1. Colored concretes or surface coatings on pavements
can be used to increase the values for this credit. Note that the reflectance value
given is solar reflectance. There is also a commonly used parameter called visible

Material Emissivity Reflectance SRI
Typical new gray concrete 0.9 0.35 35
∗
Typical weathered gray concrete 0.9 0.20 19
Typical new white concrete 0.9 0.70 86
∗
Typical weathered white concrete 0.9 0.40 45
New asphalt 0.9 0.05 0
Weathered asphalt 0.9 0.10 6

∗ Reflectance of surfaces can be maintained with cleaning. Typical pressure washing of cementitious materials
can restore reflectance close to the original value. Weathered values are based on no cleaning.
TABLE 2.7.1 Some Typical SRI Values of Pavements