Hotter days, hotter nights, and higher air pollution. You don't want more of these things, but your building could be contributing to all three if it has an old or aging roof. Learn how a building's roof could be contributing to widespread discomfort and environmental damage in your city, and what you can potentially do better.
What Is the Urban Heat Island Effect
The urban heat island effect is responsible for higher temperatures in urban areas compared to rural ones. This phenomenon is particularly potent in summer when it has the highest impact on air and water quality, urban communities, climate change, and energy demand. Heat islands form in urban areas primarily due to reduced natural landscapes and the prevalence of non-reflective, heat-absorbing materials such as conventional roofs and asphalt roads.
The areas affected by the heat island effect have 1–7°F daytime temperatures higher than in outlying areas and nighttime temperatures about 2–5°F higher.
The urban heat island causes localized climate change, whose effect decreases with the distance from the source, according to the EPA Heat Island Compendium. However, this increase in urban temperatures results in higher energy demand, particularly for HVAC cooling equipment. The electricity demand for cooling increases by approximately 1-9% for each 2°F rise in temperature due to the heat island effect.
Fossil fuels (natural gas and coal) are America’s dominant energy sources for electricity generation. Therefore, the urban heat island effect can amplify greenhouse gas emissions, increasing global warming, climate change, and air pollution.
Mitigating the urban heat island effect can positively affect the well-being of urban communities. But it may also reduce energy bills, energy consumption, and peak electrical grid loads.
Causes Of Urban Heat Island Effect
Several factors are responsible for forming heat islands in urban areas, including heat generated from human activities, urban geometry, and climate conditions. But, from the building, architecture, and construction perspective, the urban natural landscape and urban material properties are crucial.
As cities develop, natural elements such as grass, shrubs, trees, and bodies of water are replaced with pavement, asphalt roads, buildings, and other crucial infrastructure. Trees and vegetation provide shade, which can reduce ground surface temperatures. In addition, vegetation releases water into the air through a process called evapotranspiration. This process dissipates local heat and reduces air temperatures.
Buildings with conventional roofs, roads, and parking spaces are usually made from dry, impervious surfaces that accumulate heat and lead to urban heat islands. Conventional building roof systems typically have low solar reflectance. Therefore, such roofs absorb and accumulate the sun's energy, which creates concentrated urban heat islands that increase local temperatures. A similar effect occurs with other urban elements like pavements, roads, and parking lots.
How To Reduce Urban Heat Island Effect
Apart from a city's capital improvements into green infrastructure, building owners can help reduce urban heat island effects by using reflective or vegetative roofs. Both roof types also improve your commercial building's energy efficiency. So, not only can reflective and green roofs help mitigate the urban heat islands, but they may lower your energy bills, improve your building's value, and enhance the occupant's comfort.
Cool roofs are designed to reflect more sunlight energy than traditional roofing systems. Under the same summertime conditions, cool roofs can be more than 50°F (28 °C) cooler, says the US Department of Energy.
Solar energy comprises ultra-violet (UV) rays (5%), visible light (43%), and infrared radiation (52%). Many cool roofing systems are bright white because their solar reflectance primarily reflects visible light. However, some colored roofing products are designed to reflect in the "near-infrared" range, according to the EPA Heat Island Compendium. Traditional roofing materials with a low solar reflectance of about 5-15% absorb up to 85-95% of the sun's energy. On the other hand, reflective roofs can reflect more than 65% and absorb 35% or less heat.
Elevate™ cool roofing products include TPO, PVC, Ecowhite EPDM, light-colored metal roofs, and Ultrawhite granulated cap sheet modified bitumen systems. So, no matter which roofing system works best for you, Elevate stands ready to help you transition to a reflective roof.
Elevate UltraPly™ TPO roofing systems offer exceptional reflectivity that meets initial reflective surface requirements by CRCC and ENERGY STAR® requirements. Our TPO products are listed with the Cool Roof Rating Council (CRRC) and California's Title 12 Energy Efficiency Building Standards. Elevate UltraPly™ TPO SA comes with Elevate Secure Bond™ technology. It is one of the most flexible TPOs on the market* and installs faster than traditionally adhered TPO.**
Elevate PVC roofing systems provide many of the same benefits as TPO, including high solar reflectivity. But they can also endure some of the toughest flat-roof aggressors like hurricane-level winds, fire, grease, chemicals, and jet fuel. So if your commercial building is a restaurant, chemical plant, or food processing facility, or is under a higher threat from fires or aggressive chemical agents, consider using an Elevate PVC roofing system to transition to a cool roof.
So, how do vegetative roofs (sometimes called green roofs) reduce the urban heat island effect? The rooftop vegetation mitigates urban heat islands, much like the vegetation in nature — through shading and evapotranspiration.
Vegetative roofs often don't have trees, but the growing medium and smaller vegetation block sunlight from reaching the underlying roof membrane. As a result, the roof is "shading" the underlying structure and lowers the absorbed heat. In addition, the underlying membrane can last longer because it's shielded from UV radiation and protected from extreme temperature fluctuations.
Evapotranspiration cools the air and helps reduce surface temperatures. Plants absorb water through roots and carry it to their leaves. The air heat (energy) is then "spent" to evaporate the water from the vegetation surfaces and the growing medium. As a result, the rooftop temperatures are lowered, and the urban island effect is reduced.
The two main vegetative roof types are extensive and intensive vegetative roofs. Both have certain advantages. But, if you want to transition from a traditional roofing system to a vegetative, cool roof, extensive vegetative systems are much more accessible.
Elevate™ SkyScape vegetative roof systems are designed for simple installation, easy removal for roof maintenance, and modular implementation. Using Elevate SkyScape may help you quickly increase your building's energy efficiency and reduce the impact on your local urban heat island. In addition, Elevate SkyScape can reduce stormwater runoff and help you meet the related regulations. Vegetative roofs not only retain stormwater and prevent excessive runoff, but they also may act as a filter and retain dangerous pollutants like cadmium, copper, and lead, according to the EPA Heat Island Compendium.
Partner With Elevate™ To Create a Sustainable Future
Elevate™ is committed to more sustainable products and partnerships for a more sustainable future. Find an Elevate contractor near you to learn how your commercial roof could improve your community by helping to reduce the urban heat island effect.
Elevate experts and proactive partnerships will help you every step of the way to transition to an energy-efficient and sustainable future. Partner with Elevate and evolve the way you build!
* Based on the Taber Stiffness testing versus best-selling competitor TPOs
** 1 UltraPly™ TPO SA versus standard TPO from third-party testing. Results may vary.