For many years, architects, engineers and contractors believed that a roof's color, especially the choice between black and white, significantly impacted a building's environmental footprint by influencing the urban heat island (UHI) effect. UHI is a phenomenon where urban areas are warmer than nearby rural areas due to human activities and changes in the natural environment, such as deforestation and the construction of buildings, roads, and other infrastructure. The simple logic is white or “cool” roofs are reflective, absorb less heat, and help to mitigate the UHI effect. Conversely, many believe that black roofs exacerbate the UHI effect by absorbing more sunlight, thus raising the building's ambient temperature, particularly in densely populated cities. This thinking led many to choose white roofs over black roofs, and it has even led some jurisdictions to mandate specific roof colors to combat the UHI effect.
However, recent studies by the EPDM Roofing Association (ERA) have challenged this belief, finding no discernible correlation or significant impact between roof color and the UHI effect. The studies highlight building insulation technology as a more influential factor in combating the UHI effect. This shift in understanding emphasizes the importance of leveraging subject matter experts in decisions regarding commercial roofing materials and colors. Roofing professionals such as architects, consultants, and engineers bring specialized expertise in these areas to provide recommendations that best suit a building's unique requirements.
All images courtesy of Holcim.
New Insights Challenge Established Roof Color Paradigms
As communities across the nation grapple with escalating urban temperatures, some local municipalities and jurisdictions have mandated the color of roofs based on long-standing assumptions now brought into question by recent findings. The ERA research underscores that the impact of roof color on the UHI effect remains inconclusive, signaling a need for further exploration.
A critical revelation from the research points toward insulation playing a more significant role in combating UHI effects, with the data suggesting that advancements in insulation technology are making a more substantial positive impact on the UHI effect than the choice of roof color.
Digging deeper into the UHI effect, the findings identify core factors contributing to increased urban temperatures. These include:
- Reduced Natural Landscape: The loss of natural vegetation and water bodies, which cool the atmosphere, significantly contributes to the UHI effect.
- Urban Material Properties: Materials used in urban construction, like exterior walls and pavements, tend to absorb and retain solar energy, exacerbating the heat.
- Urban Geometry and Landscape: The configuration, size and layout of urban structures often obstruct wind flow and trap solar energy, contributing to higher temperatures.
- Heat from Human Activity: The heat generated from vehicles, air conditioning and other building systems further intensifiesheat in urban areas.
- Weather and Geography: Factors such as average wind speed, cloud cover, humidity, and geographical features also play significant roles in the UHI effect.