TEN YEARS AGO, the concepts of sustainable design and green-building practices were becoming mainstream for many involved in designing commercial projects. The reference to cool roofing was part of this green revolution. A small group of visionaries recognized cool roofs could play a major role in the sustainability movement. In 1998, they formed the Cool Roof Rating Council, Oakland, Calif., for the purpose of developing a fair, accurate and credible system for rating the radiative properties, specifi cally solar refl ectance and thermal emittance, of roofi ng products. Th e work and visibility of CRRC have been benefi cial to metal roofi ng. A recent project dealing with the complexity of measuring solar refl ectance on profi led metal roof panels is an interesting example of the interaction between the CRRC and metal-roofing industry.
In 2007, CRRC suggested amending the test method for measuring solar refl ectance for metal roofing because members of the council thought the typical profi les might lower the actual refl ectance compared to what was measured on flat samples. Th is was based on a theory that high ribs and angled surfaces in deep profi les could refl ect solar radiation from some surfaces and reabsorb the radiation into other surfaces. Th e result, according to the theory, might be lowered solar refl ectance for profi le panels when compared to a fl at sample.
The categories of profi led metalroofi ng panels thought to be aff ected by this phenomenon included standing seam, modular press formed (shake or shingle) and exposed fastener agricultural panels. To determine the validity of this assumption, the Pittsburgh-based Cool Metal Roofi ng Coalition developed a test program using a variety of metal-roofi ng materials provided by members of the Glenview, Ill.-based Metal Construction Association. A team of representatives from the metalroofi ng industry and Oak Ridge National Laboratory, Oak Ridge, Tenn., studied nine different profi les in 14 diff erent colors representing low, medium and high solar refl ectance values at a weathering farm in Fort Myers, Fla. Th e location off ered uninterrupted sunshine, which sped the test program.
Th e test method chosen was ASTM E1918, “Standard Test Method for Measuring Solar Refl ectance of Horizontal and Low-Sloped Surfaces in the Field,” which is recognized by CRRC as an accepted method for measuring solar refl ectance on roofi ng products with variegated color and/or profi led surfaces. In ASTM E1918, an albedometer, which is a device that measures solar radiation, is positioned approximately 3 feet (0.9 m) above the surface of a 10- by 10-foot (3- by 3-m) sample.
The albedometer is fi rst oriented toward the sky to measure the amount of solar radiation coming from the sun. Th en the albedometer is oriented facing the sample and measures the amount of solar radiation refl ected from the surface. Th e ratio of the two levels of solar radiation is the average solar refl ectance of that surface. Triplicate measurements of the incoming and refl ected levels of solar radiation were used to determine the reported average solar refl ectance of the test materials. Th e test only takes minutes; values are taken when the albedometer equilibrates. Th e ASTM E1918 test method has many limitations and stipulations on the technique, such as being valid only during cloud-free days, limited times of day representing solar noon in a given location, interference from perimeter surfaces, etc. Th e test method also has no precision and bias information included in the standard.
Using the ASTM E1918 method, the team found no statistically significant diff erences in the solarrefl ectance values measured on fl at samples of the metal (painted and unpainted) compared to profi led panels manufactured from the identical fl at material for most of the products tested. In one case with a very-deepprofiled product not normally used for roofi ng over conditioned space, the team found a statistically signifi cant diff erence in the solar refl ectance of the fl at versus profi led condition. However, the product in question is one that would not be commonly listed on the CRRC directory for roofi ng of conditioned buildings. It only was included in the experiment for scientifi c purposes. Th e comprehensive test results were presented to the CRRC Technical Committee and CRRC board of directors in 2008. Th e board approved a change to the CRRC-1 procedure that added the following language under “Section 3.5.1 (B) 4 Standard Production Line Roofi ng Products, Except Variegated Products”: Profiled metal roofi ng products shall be rated using fl at samples of the same color and material. Ratings for these samples may be applied to standing seam, agricultural panel and modular/metal shingle profi le types. Exceptions: All other profi le types of any solar refl ectance shall be rated using profi led test samples and the solar refl ectance shall be measured using ASTM E1918. As a result, the metal-roofi ng industry can continue to use any of the CRRCapproved test methods for measuring initial and aged solar refl ectance of products with fl at samples representing the material used for the profi led product. Th is applies to those types of profi les mentioned above. One type of profi le that has not yet been addressed is a tile facsimile metal-roofi ng panel. Th e metal-roofi ng industry will be studying CRRC’s approach to that profi le in the near future.
Scott Kriner is president of Macungie, Pa.-based Green Metal Consulting Inc. and founding chairman of the Cool Metal Roofi ng Coalition, Pittsburgh. He can be reached at email@example.com or (610) 966-2430.
FOR MORE COOL METAL ROOFING INFORMATION
Cool Roof Rating Council | Oakland, Calif. | www.coolroofs.org
Cool Metal Roofi ng Coalition | Pittsburgh | www.coolmetalroofi ng.org
Oak Ridge National Laboratory | Oak Ridge, Tenn. | www.ornl.gov
ASTM International | Washington, D.C. | www.astm.org
A CRRC History
The Oakland, Calif.-based Cool Roof Rating Council was established in 1998 with 25 founding members. Today, the organization boasts 176 members and many accomplishments that have signifi cantly demonstrated the value of cool roofing in green building. The fi rst was the launch of the Product Rating Program in 2002 and its centerpiece, the Rated Products Directory, which is available online at no cost. The directory currently contains 1,000 products. CRRC’s rated products have been tested for initial solar refl ectance and thermal emittance according to industry standard methods prescribed by the CRRC program. A product that is listed with initial measurements must be exposed outdoors at specifi c CRRC-approved commercial weathering farms and measured for three years. The product then is placed in the CRRC directory, and a label depicting the CRRC rating can be used for promotional purposes and shipping, according to provisions outlined in the CRRC program. CRRC gained another level of recognition in 2005 when the Sacramentobased California Energy Commission added a cool-roof requirement to its Building Energy Code, Title 24, for low-slope, air-conditioned commercial buildings. CRRC is the sole supervisory entity for solar-refl ectance and thermalemittance ratings within Title 24. In addition, when the cool-roof requirement of California’s Title 24 expands to include residential buildings and steep-slope roofs in certain climate zones this year, it will again include an exclusive reference to CRRC’s Product Rating Program. In 2008, CRRC became an Accredited Standards Developer through the American National Standards Institute, Washington, D.C. As a result, the CRRC-1 Standard for rating the radiative properties of roofi ng materials will undergo a consensus body review and be submitted to ANSI to become an American National Standard. As green building becomes even more mainstream, CRRC will continue to be a fundamental part of the sustainability industry.