Recent Research on Roof Albedo

The EPDM Roofing Association (ERA) is recommending that Federal, state and local governments, as well as regulatory bodies, pause the development and implementation of reflective roofing and cool roofing mandates. This recommendation from ERA is based on the findings of three studies funded by the Association related to roof albedo, insulation, urban heat islands, and energy efficiency These studies showed that complex and inconsistent temperature assessment protocols are being utilized in virtually all UHI evaluations, making comparisons of efficacy problematic; and then also showed that roof albedo promotes energy efficiency in only a few situations in climate zones 1-4.

“We need to develop a consistent way to measure the impact of reflective roofs, so that we can evaluate their efficacy compared to other mitigation strategies that are being used to lessen extreme heat in urban areas”, said Ellen Thorp, Executive Director of ERA. “Prudent building science requires us to call upon the Federal and state governments to conduct additional research to assess the real-world relative value of all proposed solutions that might diminish the impact of the challenge of UHI.”

For the initial study, ERA contracted with ICF, an independent consulting firm with experience in climate change, data analysis, and building science. ICF undertook an analysis of existing data and previous studies on UHI, with specific focus on the measurable impacts of the roof albedo of low-slope roofing. 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. “This does not necessarily mean that there is no correlation between cool roofs and the reduction of UHI,” according to Jason Wilen, a forensic architect with Klein & Hoffman and technical consultant with ERA. “But it points to the need to develop a consistent way to measure the impact of reflective roofing, as well as other mitigation strategies.”

To expand on the findings of the initial study, ERA commissioned a critical literature review conducted by the Nieri Family Department of Construction Science and Management at Clemson University. This comprehensive review examined over 2,000 published studies and models exploring the impact of membrane color on energy efficiency and urban heat islands, ultimately narrowing the focus to 280 references deemed relevant for in-depth analysis. According to the Clemson researchers, this exhaustive review revealed the complexity and variability in findings regarding the relationship between roof albedo, urban heat islands (UHI) and energy efficiency. The discrepancies stemmed from numerous factors, including variations in roof type, climate, and geographic location. Additionally, inconsistencies in data collection methods, the predominance of simulation-based studies, and short data capture durations contributed to the lack of definitive conclusions. Other influential factors included the impact of winter season “heat penalties,” interactions between varying building heights, and the absence of consistent comparisons among urban tree canopies, roofs, hardscapes, asphalt surfaces, and insulation thickness. As Dr. Dhaval Gajjar, a lead researcher on the project, noted, “In many instances, more recent studies based their conclusions and recommendations on widely distributed prior studies, which now must be considered dated or incomplete given the availability of updated research.”

The third research study commissioned by the EPDM Roofing Association (ERA) focused on assessing the relative impacts of roof albedo and insulation on energy efficiency, economic benefits, and emissions reductions during roof replacements. Specifically, the study evaluated the energy performance of installing code-compliant roof insulation compared to implementing cool roof interventions under various scenarios. The findings highlighted that insulation, rather than roof reflectivity, often provides the most significant energy benefits. The study’s methodology included analyzing energy savings, calculating economic benefits, and estimating emissions reductions across four building types in nine cities spanning three ASHRAE climate zones. The baseline conditions assumed a building constructed in 2005 with its roof replaced 17 years later, adhering to the original code requirements at the time of construction.
Three intervention scenarios were modeled:

a black roof with 2019 code-compliant insulation levels;
a highly reflective roof with 2004 baseline insulation levels; and
a highly reflective roof with 2019 code-compliant insulation levels.

Key findings of the study include:

Adding insulation during roof replacements proved to be cost-effective in most cases, regardless of whether the roof was black or white.
Switching from a black roof to a white roof without upgrading insulation was not cost-effective in certain building types and climate zones, particularly for
warehouses in Climate Zones 4A, 4B, 4C, 5A, and 5B, and for medium office buildings in Climate Zones 4C, 5A, and 5B.
The energy benefits of combining insulation with cool roofs were not additive, as increased insulation levels tended to diminish the incremental advantages of
reflective roofs.

The study concluded that while cool roofs can provide modest energy savings in warmer climates when installed with traditional insulation levels, their benefits decrease when paired with higher levels of insulation and in colder climates. This reduction underscores the limited role of cool roofs as a standalone mitigation strategy for roof replacements required to meet the prescriptive insulation standards of ASHRAE 90.1-2019 and the IECC. The findings further emphasize the importance of prioritizing insulation upgrades to achieve greater energy efficiency during roof replacements.

All of the research studies exposed inconsistencies in measuring the impact of reflective roofing on the severity of UHI, as well as on the amount of energy being used,” according to Wilen. “Our focus, as we consider policies that are designed to lead us to a future where energy ecfficiency of a building can be improved and the UHI effect can managed and even diminished, must be based on science, not supposition.”