Eco-structure’s January/February issue included an article by Tom Hutchinson titled, “Challenging What’s Cool: Is the Exponential Growth of Cool Roofing an Impending Catastrophe?”, “cool roofing,” page 38. Although Hutchinson’s comments may have some merit, the overall implications about cool roofing are misleading. A reader would be left with the impression that cool-roofing materials are problematic and tend to fail in virtually all applications. It is our view that Hutchinson’s examples do not point out failures specific to cool roofing but instead failures in roof design. For example, with proper design and installation of insulation and vapor barriers, the condensation failures noted in the article would be avoided.
Hutchinson opens his article by declaring that, when it comes to cool roofs providing an environmental benefit, “nothing could be further from the truth.” Yet studies conducted on actual roofs show their potential for energy savings. In his 1997 article in Energy and Buildings
, Paul Berdahl, a scientist at Lawrence Berkeley National Laboratory, Berkeley, Calif., summarizes several studies: According to “Preliminary survey of the solar reflectance of cool roofing materials” by Berdahl and S. Bretz, field tests in Florida resulted in cooling-energy savings ranging from 10 to 43 percent with the application of high-albedo coatings to various roofs. Utility-coincident peak demand (5 to 6 p.m.) was reduced by 16 to 38 percent in the same buildings. Energy savings were significant even with well-insulated roofs. In Mississippi, cooling-energy savings of 22 percent for the summer were achieved through the application of a high-albedo coating while there was no penalty in the winter. In Sacramento, Calif., several buildings had cooling-energy savings of 40 to 50 percent and 30 to 40 percent peak-demand reductions through high-albedo roof retrofits.
These studies show cooling-energy savings ranging from 10 to 50 percent in different venues. In addition, the Washington, D.C.-based U.S. Environmental Protection Agency’s Energy Star program estimates typical cooling reduction of 10 to 15 percent. Because space cooling is, on average, almost 18 percent of a building’s energy use according to the Washington-based U.S. Department of Energy’s “Buildings Energy Data Book,” a cool roof can reduce a building’s total energy use by 2 to 10 percent. The benefits of cool roofs are most significant in climates where there is a high need for air conditioning because of summertime heat. EPA and DOE have developed calculators to help architects, building owners and roof consultants determine the energy-savings potential of a cool roof. (Visit www.roofcalc.com and www.ornl.gov/sci/roofs+walls/facts/CoolCalcEnergy.htm, respectively.)
We agree with Hutchinson that roofs must be considered as a whole system but would argue that cool-surfacing materials are an important component of an energy-efficient roof. The use of cool roofing does not negate the need for appropriate roof-system-design considerations, but, as demonstrated by the mentioned studies, cool roofs can have a positive impact on energy savings and provide other environmental benefits, such as a reduction in the urban-heat-island effect when properly specified and installed.
Hutchinson is a knowledgeable roof consultant and architect, especially in regard to proper roof design and construction. He also serves as a technical consultant for the Bethesda, Md.-based EPDM Roofing Association, a trade association whose members primarily produce non-reflective, black roofing materials. Architects and consultants who read his article are advised to seek objective information about applying cool roofing, taking into consideration proper roof-system design and installation, as well as climate considerations.
Cool Roof Rating Council,
I appreciate that the CRRC staff and board members have taken the time to read my article, which was requested by Christina Koch, eco-structure’s editor in chief, after she had heard several stories about cool-roof failures from readers. I am encouraged that an association concerned only with one component of a roof system has come to appreciate that roofs act as systems, and one-component-design solutions are a recipe for disaster.
However, I must address inaccuracies and mistakes within your letter:
1. I am the technical consultant for ERA whose primary members—Carlisle SynTec, Carlisle, Pa., and Firestone Building Products, Indianapolis—produce EPDM. These companies also control the lion’s share of reflective membranes used in North America and do not share CRRC’s single-component philosophy.
2. Your suggestion that space cooling is almost “18 percent of a building’s energy usage” is inaccurate. According to the “Buildings Energy Data Book,” September 2008, cooling accounts for 12.7 percent primary (at the source) energy and 8.2 percent of the total energy use for a building owner.
3. The 1997 article referenced by Paul Berdahl does not conclude with verification of energy savings but only references in its introduction energy savings from a previous study. The referenced paper, “Preliminary survey of the solar reflectance of cool roofing materials,” from the early ‘90s, uses thermal R-values that are approximately 70 percent below those required today by the Atlanta-based American Society of Heating, Refrigerating and Air-Conditioning Engineers Inc.; R-14 is used in the paper reference while R-38 is required today. Furthermore, the referenced paper identifies construction methods predominately used in California (wood deck with insulation below deck versus metal roof deck with insulation above deck, which dominates most of North America) as its basis.
4. The 1997 article basically discussed various roof coatings with emphasis on reflective coatings, which may be acceptable practice in California but can have adverse effects if utilized in colder-climate regions. The formation of condensation below mechanically attached roof membranes in ASHRAE Zones 3 and above is significant. I have clients with wet roof systems as far south as Kentucky.
You mention vapor retarders would stem the formation of condensation. This is not necessarily true when considering the cool-roofing mantra that you can decrease the thermal value of your roof with a cool-roofing membrane. Consequently, you may only be moving the condensation point. Placing a vapor retarder below the insulation, which is reduced because of the idea that it’s not needed with a cool-roof membrane, may leave the vapor retarder in a position to reach the dew point and result in condensation formation below the vapor retarder. This could result in great interior moisture accumulation, in part because the insulation facer is not there to absorb some of the moisture.
Proponents of a single-component roof solution, such as the Washington-based U.S. Green Building Council and EPA, among others, have led architects to believe that by specifying only a white roof cover as an adequate roof system everything will be fine. Well, all is not fine. USGBC’s desire for positive building pressure has created a situation where HVAC systems are pushing warm, often moist, air to a loose exterior cladding material, creating recondite problems. The unintended consequences are wreaking havoc across the Midwest. Those who continue to specify cool-roof membranes in a lemminglike nature certainly will see their liabilities rise.
I am not anti-cool roofing, but when those with little roof-system knowledge promote and encourage substantial construction methodology changes based only on number crunching without anticipating the possible manifestations, a voice from the roofing industry needs to be heard. All roofs should be designed as systems by those knowledgeable in roof-system design, and the selection of the roof cover should not be mandated by code. It is nice to see that CRRC agrees.
AIA, FRCI, RRC, principal
Hutchinson Design Group, Barrington, Ill.