The cool roofing debate continues
This letter is in response to "Still cool after all these years: White reflective roofs stand up to scientific scrutiny," October 2013 issue, page 38, by Stanley P. Graveline, vice president of technical services for Sika Sarnafil, Canton, Mass.
Carlisle Construction Materials, Carlisle, Pa., a manufacturer of roof insulation and black and white single-ply membranes, agrees wholeheartedly that white membranes can be part of an energy-efficient roof system. In warm, southern climates where the bulk of energy bills come from air conditioning, reflective cool roofs can cut energy bills, decrease stress on the power grid and reduce natural resource consumption.
But in cold, northern climates, building owners typically spend much more on heating than air conditioning. Government data shows heating a building consumes about five times more energy than cooling it. Unfortunately, white roofs often are installed and even mandated in cold-climate regions where they do not deliver major energy benefits, and this can lead to undesirable and unintended consequences.
It is appropriate the article was published in October 2013 because in the October 1998 issue, page 32, Professional Roofing published "Cool systems for hot cities." Following are some statements from the article: "Researchers at Lawrence Berkeley National Laboratory (LBNL) and the Florida Solar Energy Center (FSEC) have measured cooling energy savings of up to 60 percent for individual homes where white roof coatings were applied to dark roof systems. Homes with the highest energy savings were those that had cooling ducts running through the attics and little or no attic insulation. For these homes, hot attics have the most detrimental effects In addition, a small amount of insulation (e.g., R-5) allows much of an attic's heat to transfer directly to the house below. But for moderately insulated buildings, roof color will not make a large difference in energy savings."
It's not surprising that, in a warm climate, using a light-colored reflective roof on a building with little or no insulation (such as R-5) and cooling ducts running through the attic will yield significant savings in air conditioning costs. But let's take a look at some important changes that have taken place during the past 15 years.
Typical insulation levels have increased dramatically in residential and commercial buildings. It is not uncommon for R-25 insulation to be used in commercial applications. As noted 15 years ago: "For moderately insulated buildings, roof color will not make a large difference in energy savings."
In addition, numerous studies and organizations have analyzed a roof color's effect on energy savings. An October 2013 study published by researchers from Oak Ridge National Laboratory (ORNL), Oak Ridge, Tenn., included the following summary: " It is important to note that based on acceptable industry standard calculations in the current business environment, static reflective roofing does not provide an energy cost savings in cooler or temperate climates. In fact, it can be detrimental to overall energy costs to employ roofing with high SRI values."
A study conducted by Ashley-McGraw Architects, Syracuse, N.Y., and CDH Energy Corp., Syracuse, compared roofs with black and white membranes over 4 inches of insulation in Jamesville, N.Y. The study accounted for such contributing factors as the sun's angle and snow and cloud cover. A 30 percent heating penalty was documented in the building with a white roof, which exceeded the cooling savings realized in summer.
As people question the logic of using cool roofs in areas of the U.S. where energy bills are dominated by heating costs, some pro-reflective roofing groups are shifting their emphasis to other arguments, such as the mitigation of urban heat islands. However, a 2011 Stanford University study by environmental engineering professor Mark Z. Jacobson and graduate student John E. Ten Hoeve ("Effects of Urban Surfaces and White Roofs on Global and Regional Climate") refutes the claim white roofs help address urban heat islands. Reflective membranes do just thatthey reflect heat into the atmosphere or onto surrounding surfaces. Conversely, dark-colored membranes absorb solar energy, which can reduce heating costs, natural resource consumption and, consequently, carbon dioxide emissions.
Several other factors must be considered when white roofs are installed in northern climates. For instance, it is a law of physics that warm, humid air condenses on cool surfaces that are below the dew point temperature. Consequently, white roofs in cool northern climates can be prone to condensation problems that can, in turn, lead to mold development, reduced insulation R-value and increased energy consumption.
Most major roofing manufacturers exclude condensation-related issues from their warranties and include precise language in their specifications regarding how to avoid these problems. Architects and contractors should take note they are the ones liable for condensation issues related to their roof system designs and installations. A dark-colored roof that minimizes the potential for condensation problems is often a better choice in a cool climate area. Slip and fall hazards from frost, dew or ice in addition to added roof cleaning costs also are factors to be considered when contemplating using a white roof in northern climates.
Several roofing manufacturers that are able to supply a range of dark- and light-colored roof systems offer a more balanced approach to roof system selection to ensure the proper match of a roof type to a building's use and location. As the debate about sustainable practices continues, it is becoming increasingly clear it is wise for roofing professionals and building owners to embrace a holistic system approach.
Craig A. Tyler, AIA, CSI, CDT, LEED-AP BD+C
Carlisle SynTec Systems
Graveline responds: I appreciate Mr. Tyler taking the time to provide his feedback. Cool roofs on buildings with large amounts of insulation located in northern climates will, of course, result in less energy savings than they would over more lightly insulated roofs located in southern climates. On that we can all agree!
Quantifying the actual amount of energy savings using various models can be challenging. Taylor highlights an ORNL report noting in the "current business environment" cool roofs may not be beneficial in cooler climates while my article features another ORNL study showing additional insulation is required below a dark roof in all climates to achieve energy parity with a cool roof.
The Jamesville, N.Y., study cited yields some interesting information. However, the conclusions highlighted must be considered in the context of a couple of key elements of the study. The buildings are heated, but as the authors note: "The correctional facility does not have cooling" though they conducted their assessment "assuming the facility did have cooling." Their conclusion that "heating losses and cooling savings tended to cancel out" was based on assumed heating costs of $1 per therm and electricity costs of $0.12 kWh.
According to the U.S. Energy Information Administration website, the average heating cost for New York commercial customers in 2010, the one full year covered in the study, was $1 per therm while the average cost for electricity was $0.16 kWh. Presumably, the cooling savings resulting from the theoretical cooling system would have done much more than cancel out any heating losses at an average cost of electricity 33 percent higher than assumed, as was apparently the case in the state at that time.
With regard to the urban heat island effect, the authors of the Stanford University study stated reflective roofing contributes to urban-scale cooling but may contribute to global warming though they acknowledge the global finding is "highly uncertain." Furthermore, other third-party studies conducted in Europe and the U.S. (mentioned in my article) support LBNL's findings on the overall benefits to be accrued by a combination of cool technologies (cool roofs and cool pavements and vegetation) and if anything, find them to be conservative. The third key element in the cool roof energy equation is peak demand reduction, an ever more important issue in all climate zones.
Even in locations where net energy savings may be modest, combined with the additional benefits of reduced peak demand and a contribution to the reduction of the urban heat island effect, cool roofing technology provides a comprehensive package of benefits even in northern climates.
Lastly, as was noted in the "Guidelines for Selecting Cool Roofs," there is no field data to support the claim that light-colored roofs are more prone to condensation and/or moisture-related issues than dark-colored roofs. With more than 5 billion square feet of light-colored thermo-plastic membranes (without considering other forms of cool roofs) installed in northern states during the past decade alone, architects, consultants, contractors and manufacturers would be overwhelmed with claims, which clearly has not been the case. In fact, the use of various light-colored materials of all types continues to grow.
So here I am with my eyes upon an image of a building resembling a futuristic pilgrim's hat on page 38 of Professional Roofing's October 2013 issue. My eyes span across the title, "Still cool after all these years."
"Here we go again," I think, fearing this will be another attempt to convince me white roofs are the panacea for the world's energy problems, they are being unfairly scrutinized and anyone who believes otherwise is living inside of a conch shell on some deserted island.
I soon realize the article was not written to educate me concerning new developments in thermoplastic technology. If that were the intent, it fails. To the contrary, it is not educational at all. The article opens rather defensively and echoes the author's ongoing struggle to support a product idea that puts food on his table yet demands I accept his assertion, ingest it and wash it down with a tall glass of Kool-Aid!
I quote: " The most significant development in the low-slope commercial roofing industry during the past 15 years is the increase in awareness and adoption of the cool roofing ‘concept.'"
In the author's opinion, this is the most significant development for the whole industry in 15 years? Why, I wonder? Although the article states the obvious when it notes PVC has been around since the 1960s in Europe and the 1970s in North America, it fails to address the question of why it took three decades for it to be sponsored as an energy-saving solution. Never before 1990 was a white membrane marketed this way.
After thoroughly investigating all the misleading data in this article, the obvious conclusion and the primary motivating factor is the "concept" sells!
Therefore, being well-equipped with the preliminary energy studies furnished by national laboratories, the manufacturers' marketing departments took to the streets and began infesting the industry with "cool roofing" propaganda all the while opposing anyone who intelligently contested their position that white roofs are beneficial everywhere. These marketing efforts were enough to improve market share.
The TPO industry more than doubled its market position from 7.1 percent of new construction and 5.3 percent of reroofing in 2002 to 16.26 percent of new construction and 14.06 percent reroofing in 2006, according to NRCA's 2006 Annual Market Survey.
Roofing companies jumped into the white roofing movement. Shifting their focus to capitalize from these energy initiatives, they adjusted their business models to meet the sector's growing demand. Currently, in every part of the U.S., roofs are being replaced with white membranes; material prices continue to skyrocket; manufacturers are raking in profits; and the government is fluffing its budgets to support energy reduction initiatives.
Meanwhile, "professional" roofing companies continue to expose themselves to much greater risks associated with cool roofing in cold climate zones, such as condensation entrapment that causes premature material degradation, decreased R-value, mold spore proliferation and a decreased wind-uplift value caused by fastener degradation.
According to a 2011 SPRI study, 30 percent of reflective roofs in cold climates fail because of condensation that develops within the systems. This is not a simulated study based on algorithms; these are in situ observations. Why isn't the author discussing this fact?
From a biased position, this article reiterates and rehashes material such as the 1998 Lawrence Berkley National Laboratory (LBNL) study published in 2001 while blatantly ignoring more current opposing data that appears, oddly, within the same studies the author cites, such as "Guidelines for Selecting Cool Roofs, 2010" published by the Center for Sustainable Energy Systems. Mentioned in the study was this statement: "Climate has the biggest impact on energy savings. Cool roofs achieve the greatest cooling savings in hot climates but can increase energy costs in colder climates due to reduced beneficial winter time heat gains."
The same study cautions: "White roofs do not perform equally everywhere. Information gathered from the U.S. Department of Energy clearly demonstrates that heating is a much more significant factor in energy usage than cooling. For instance, Grand Rapids, Mich., has 7,153 heating degree days versus 508 cooling degree days per year, which means heating equipment runs approximately 14.3 hours for every one hour that cooling equipment runs."
So regardless of the sun's angle in winter, lessened amount of winter daytime hours and snow-covered roofs, as this article supports, it has been determined by many professional roof consultants and national laboratories who study building materials that a black roof still is more energy-efficient in climates as far south as Albuquerque, N.M. How these facts were overlooked bewilders me.
Furthermore, in an attempt to support the claim of energy reductions, the author refers to big-box store studies. Most buildings do not cool as much airspace as big-box merchandisers. In fact, according to the 2007 Buildings Energy Data Book, 31 percent of the total energy consumption by retail buildings is from heating and only 6 percent is from cooling.
In the article, the author uses data provided by professional laboratories to support that a white membrane is a tool to reduce overall energy consumption while simply ignoring the fact it will not in most climate zones. So given the contradicting nature of the data provided, I feel this article fails to clearly present evidence to endorse white roofing in a cold climate.
When discussing the soiling behavior of a white roof, I again find the article's information to be distorted. The author states: " Cleaning (a white membrane) can restore practically 100 percent of many products' initial reflectivity." It doesn't read cleaning will definitely restore 100 percent of all products' reflective properties. Let's call a spade a spade.
According to the paper "Saving Energy by Cleaning Reflective Thermoplastic Low-Slope Roofs," the discovery was that cleaning a white thermoplastic membrane varied greatly depending on the method and the membrane.
Again, contrary to this author's opinion, in "Guidelines for Selecting Cool Roofs," July 2010, it reads: "Although annual cleaning can restore up to 90% of initial reflectance, the energy cost savings alone do not warrant the cost. In the more moderate climate of Knoxville, the advantage for washing the roof is only about 1¢ per square foot after three years of exposure for a highly reflective thermoplastic membrane with R-15 insulation."
So where is the savings for buildings in a cold climate?
This article has done well in reiterating the major positions of those who advocate white membrane installations. Then again, I would not expect anything less from a leading manufacturer of white PVC roof membranes.
But what about other manufacturers who sell black and white membranes? What do they say? Are they as selective about what color membrane we should use? Do they slant information to gain market share for one kind over another?
It appears the article is far from being an objective examination of the data; in actuality, it is nothing more than a promotional ad in the guise of a manufacturer's contribution to an unbiased trade magazine.
Jeremy M. Penney
Dura-Ply Roofing Corp.
Graveline responds: Beyond some of the more general topics contained in the previous letter, Mr. Penney highlights other specific points that merit a response.
He notes a 2011 SPRI study shows "30 percent of reflective roofs in cold climates fail because of condensation that develops within the systems" and goes on to ask "Why isn't the author discussing this fact?" Clearly, he must have missed that section of my article.
I did, in fact, highlight the 2011 SPRI report (page 43). I noted no moisture was found within seven of the 10 roofs surveyed by SPRI during the winter survey. Presumably, the three roofs in which moisture was observed on the backside of membranes represent the "30 percent of reflective roofs in cold climates (that) fail" referenced in Penney's letter.
In the same report, SPRI documented the results of WUFI simulations carried out for the climate zone in which the surveyed roofs were located; based on the results, SPRI concluded "within the parameters used in this study, both [black and white] roofs returned to a dry condition during the course of the year, which was consistent with field test cut observations."
Most important, SPRI stated for all 10 roofs surveyed, which were up to 12 years old, that "no detrimental effect to the roofing system was noted."
The "Guidelines for Selecting Cool Roofs" Penney references were prepared for the Department of Energy's Building Technologies Program and ORNL. The quote in my article regarding condensation within roof systems was taken from page 20 of this document.
It is unclear to me as to how much more I can "call a spade a spade" with regards to soiling when I clearly state roof cleaning is rarely done! That is the reason LBNL and others use conservative aged reflectivity values in their modeling.
This topic is an important one. Although I appreciate Penney taking the time to write, we should avoid hyperbole if we are to have a reasoned debate.