UHI Tactics: How Can We Measure?

Management guru Peter Drucker is frequently quoted as saying, “If you can’t measure it, you can’t manage it.” There is some question about whether Drucker was really the author of this statement. Regardless, there’s an important message here for those of us who work in and around the roofing industry. It’s impossible to imagine an architect, a specifier, or a contractor setting out to design or repair a roof without accurately measuring the components each step of the way.

It’s this focus on measurement that has informed much of the work of my organization, the EPDM Roofing Association, or ERA, for the past two decades. In fact, ERA’s mission, beginning with its founding in 2003, has been to provide science-based information about our products, to ensure that they are appropriately used to deliver an optimized performance to our customers. With that goal in mind, we have supported research to investigate issues such as the life expectancy of EPDM, its resistance to hail, and its energy efficiency when installed with the recommended amount of insulation.

Based on this tradition of research to assess the performance of our products in a variety of situations, two years ago ERA embarked on a study focusing on one of the most important challenges we face. Urban heat islands (UHI) are areas that experience higher temperatures than outlying suburban and rural areas. This past summer, the United States experienced some of the most extreme temperatures in its history, and more than four out of every five Americans live in cities that experienced this extreme heat. This concentrated heat threatens the wellbeing of those who experience it, especially individuals and communities that are more vulnerable due to health, social, economic, or other reasons.

Specifically, the ERA-funded research looked at the impact of “cool roof” mandates in urban areas, and the efficacy of these mandates in reducing the impact of urban heat islands. To conduct our study, we contracted with ICF, an independent consulting firm with experience in climate change, data analysis, and building science, to review and contribute to the research and analysis about cool roofs and UHI. ICF undertook a review of existing data and previous studies on UHI, and compared the temperature trends of similar cities within a pair. One of the cities in the pair had a cool roof mandate and one did not. In a later phase, ICF also looked at a dozen cities and compared the cities to themselves. ICF measured their temperatures over an extended period of time starting with when there were only a few cool roofs in the area and ending after there were more cool roofs.

Research Study Results

The results surprised us, but not for the reasons you might expect. ICF’s analysis of temperature data for cities with cool roof mandates found no discernable correlation between the imposition of cool roof mandates and a reduction in UHI. The key words here are “no discernable correlation.” ICF found that the data they reviewed showed that complex and inconsistent temperature assessment protocols are being utilized in virtually all UHI evaluations, making comparisons of efficacy problematic. 

The two-year effort of ICF found that the presumed “real world behavior of urban temperatures and reflective roofs could not be verified due to the existing uncertainty in measuring the very factors that reflectivity allegedly help cure.” Put another way, there is no consistent, universally used system of measurement to determine the value of a variety of efforts to mitigate urban heat islands. This includes not only roofing, but also the potential mitigating effects of vegetation, cool pavements, and more effective planning.

Based on the findings of this study, or lack thereof due to lack of a consistent measuring system, ERA is recommending that we pause the emphasis on reflective roofing mandates as the preferred deterrent to the formation of UHI.

We are encouraging federal and state governments to conduct additional research to assess the relative value of all tactics that might diminish the impact of UHI. This will require a scope of study well beyond the abilities of any individual companies or academic institutions. And it will need a consistent, widely agreed-upon system to measure the efficacy of the variety of tactics currently being used. To ensure that we move forward to mitigate the impact of urban heat islands, we need to consider all potential mitigation tactics and accurately measure their relative efficacy.

If you can’t measure it, you can’t manage it, and — at this point — we can’t measure it.

Abut the author: Ellen Breipohl Thorp, M.A., CAE, is Executive Director of the EPDM Roofing Association. For more information about the ERA, visit epdmroofs.org.