A Primer on Cool Roofing Terminology
Definitions of the most common technical terms to help you
better understand cool roofing products and their opportunities.
• Solar Reflectance (SR) - The SR value indicates the fraction of near-infrared
solar radiation that is reflected back from a material's surface. It is typical
to rate SR values on a scale from 0.00 to 1.00, where a material with an SR of
1.00 is the most reflective (100% reflected back). For example, most Landmark
Solaris™ colors have an initial Solar Reflectance of 0.26. Solar Reflectance
is sometimes expressed on a scale from SR00 to SR100. Both XT™ 25 (Star
White) shingles and Landmark Solaris shingles (most colors) have a Solar Reflectance
of about SR26.
• Thermal Emittance (TE) - TE is a measure of a material's ability to release
(emit) absorbed heat. It is rated similarly to SR, typically on a scale from
0.00 to 1.00, where 1.00 is the most emissive. TE is sometimes rated from TE00
to TE100. Where cool roofing is desired, a higher TE value is considered better
since more of the absorbed heat can escape.
• Cool Roof - A "cool" roof is one that not only reflects solar
heat away from the exposed roof surface to a more-than-typical extent (thus reducing
heat absorption) but also easily emits a certain amount of the solar heat that
is absorbed by radiating it from the exposed surface of the roofing. The reflected
and emitted heat is sent back into the Earth's atmosphere and/or out into space.
A "cool" roof literally stays cooler than a non-cool roof. Two physical
properties are used to define the 'coolness' of a roof - Solar Reflectance (SR)
and Thermal Emittance (TE). Cool roofs work like white clothing does in the summer
sun. Some products, like those in CertainTeed's CoolStar™ line and our
FlintCoat™ W roof coating, are literally white in color. However, a roof
need not be white to be considered "cool". CertainTeed Landmark Solaris
shingles are available in very attractive dark colors and have Solar Reflectance
values as high as or higher than standard white shingles! Symphony™ Slate
also has relatively high SR values (all above SR25).
• CRRC - The Cool Roof Rating Council publishes the Solar Reflectance and
Thermal Emittance properties of roofing products (both initial values and after
three years of weather exposure) as determined by an independent, third-party
testing laboratory. Their online Rated Products Directory is available to the
general public at no charge, and it allows comparison of rated values of various
product types and brands. The CRRC is presently the only source of radiative
properties (SR and TE) that California allows as proof of compliance to the California
Energy Code (CA Title 24, Part 6). A typical CRRC label looks like this one for
Landmark Solaris (Max Def Burnt Sienna):
• Solar Reflectance Index (SRI) - SRI is a single calculated value that
indicates a roof's ability to reject solar heat by mathematically combining the
contributions of both SR and TE. It is defined such that a standard black (reflectance
0.05, emittance 0.90) is SRI=0 and a standard white (reflectance 0.80, emittance
0.90) is SRI=100. Materials with higher SRI values are the coolest choices for
roofing. Due to the way SRI is defined, particularly "hot" materials
can have slightly negative values, and particularly "cool" materials
can have values exceeding 100.
• LEED - Leadership in Energy and Environmental Design. LEED consists of
a series of "green" building programs developed and administered by
the U.S. Green Building Council (USGBC). LEED programs use rating systems for
building designs where points are assigned for specifying particular design elements
and/or materials, and several levels of "LEED certification" can be
achieved. It is important to know that individual products do not, by themselves,
earn LEED points for the building. Each acceptable product used in the building
contributes only a portion toward meeting the credit's criteria for earning a "point".
Visit www.usgbc.org for more details. Many CertainTeed roofing products can contribute
to LEED points. Visit our "CertaSpec" program to determine how each
of our products contributes. This patented tool is unique in the industry, so
use it often!
There are a growing number of organizations that are developing their own building
design rating systems to compete with LEED. One that has gained traction in the
U.S. is the NAHB Model Green Home Building Guidelines.
• NAHB Model Green Home Building Guidelines - Like LEED, this program assigns
points for design elements and building materials that are deemed "green".
Three levels of achievement exist: Gold, Silver, and Bronze.
• ENERGY STAR¨ - "Energy Star" is a joint program of the
U.S. Environmental Protection Agency (EPA) and the U.S. Department of Energy
(DOE). It has two main goals - to help citizens save money and to protect the
environment by promoting energy efficient products and practices. See http://www.energystar.gov/roof-products for
more information on Energy Star rated roofing products. Click on "Find
a Product" and take a look at the wide variety of CertainTeed Roofing products
that are Energy Star rated. The asphalt based roofing products listed in Energy
Star are eligible for ARRA tax credits.
• ARRA - American Recovery and Reinvestment Act. This federal law was enacted
in early 2009 in order to help stimulate the US economy. Tax credits of 30% of
the roofing cost, up to a maximum of $1,500, are available in tax years 2009 and
2010, when homeowners (for existing homes only) install Energy Star rated asphalt
roofing products such as Landmark Solaris shingles or CoolStar modified bitumen
rolled roofing. Installation or labor costs are not eligible for the tax credit. Roof
coatings and non-asphaltic roofing materials, except some metal roofs, are NOT
eligible for the tax credit. See http://www.energystar.gov/tax_credits for details.
• Urban Heat Island - The DOE defines "Urban Heat Island" as
a built up area (typically a city) that is hotter than nearby rural areas. The
annual mean air temperature of a city with 1 million people can be 1.8 - 5.4¡F
(1 - 3¡C) warmer than its surroundings. In the evening, the difference
can be as high as 22¡F (12¡C). Heat islands can affect communities
by increasing summertime peak energy demand, air conditioning costs, air pollution
and greenhouse gas emissions, heat-related illness and mortality, and water quality.
The installation of cool roofing products is one way to help reduce Urban Heat
Islands.
|
