Reflective surfaces (climate engineering)

[2] Painting roof materials in white or pale colors to reflect solar radiation is encouraged by legislation in some areas (notably California).

Without a proper maintenance program to keep the material clean, the energy savings of cool roofs can diminish over time due to albedo degradation and soiling.

[14] Research and practical experience with the degradation of roofing membranes over a number of years have shown that heat from the sun is one of the most potent factors that affects durability.

Covering membranes with materials that reflect ultraviolet and infrared radiation will reduce damage caused by UV and heat degradation.

Contrarily, the results also reveal that it does not influence the nocturnal profiles, as a release of heat to the sky takes place throughout the night.

A 2012 study by researchers at Concordia University included variables similar to those used in the Stanford study (e.g., cloud responses) and estimated that worldwide deployment of cool roofs and pavements in cities would generate a global cooling effect equivalent to offsetting up to 150 gigatonnes of carbon dioxide emissions – enough to take every car in the world off the road for 50 years.

[22] To satisfy the consumer demands for darker colors which still reflect significant amounts of sunlight, different materials, coating processes, and pigments are used.

[24] To decrease this, other granule materials are being investigated, such as flat rock flakes, which could reduce the reflectance inefficiencies due to surface roughness.

A response paper titled "Cool Roofs and Global Cooling," by researchers in the Heat Island Group at Lawrence Berkeley National Laboratory, raised additional concerns about the validity of these findings, citing the uncertainty acknowledged by the authors, statistically insignificant numerical results, and insufficient granularity in analysis of local contributions to global feedbacks.

[36] In 2014, a team of researchers, led by Matei Georgescu, an assistant professor in Arizona State University's School of Geographical Sciences and Urban Planning and a senior sustainability scientist in the Global Institute of Sustainability, explored the relative effectiveness of some of the most common adaptation technologies aimed at reducing warming from urban expansion.

Results of the study indicate that the performance of urban adaptation technologies can counteract this increase in temperature, but also varies seasonally and is geographically dependent.

[37] Specifically, what works in California's Central Valley, such as cool roofs, does not necessarily provide the same benefits to other regions of the country, like Florida.

However, during winter, these same urban adaptation strategies, when deployed in northerly locations, further cool the environment, and consequently require additional heating to maintain comfort levels.

"The deployment of cool roofs results in a 2 to 4 millimeter per day reduction in rainfall, a considerable amount (nearly 50 percent) that will have implications for water availability, reduced stream flow and negative consequences for ecosystems.

They add that “urban-induced climate change depends on specific geographic factors that must be assessed when choosing optimal approaches, as opposed to one-size-fits-all solutions.”[38] A series of Advanced Energy Design Guides were developed in cooperation with ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers), AIA (The American Institute of Architects), IESNA (Illuminating Engineering Society of North America), USGBC (United States Green Building Council) and US DOE (United States Department of Energy) in 2011.

For buildings located in warm climates, this measure is worth consideration.”[40][41] The Copper Development Association has conducted several studies, beginning in 2002, which examined the elevated temperatures of wiring inside conduits at and above various color roof materials.

"[43] When the sunlight strikes a dark rooftop, about 15% of it gets reflected back into the sky but most of its energy is absorbed into the roof system in the form of heat.

MEER is a nonprofit proposing the use of recycled materials to manufacture mirrors and polymer reflective films for potential widespread use on rooftops and in open spaces such as farmland.

[50] Some papers have proposed the deployment of specific thermal emitters (whether via advanced paint, or printed rolls of material) which would simultaneously reflect sunlight and also emit energy at longwave infrared (LWIR) lengths of 8–20 μm, which is too short to be trapped by the greenhouse effect and would radiate into outer space.

In a 2001 federal study, the Lawrence Berkeley National Laboratory (LBNL) measured and calculated the reduction in peak energy demand associated with a cool roof's surface reflectance.

[54] LBNL found that, compared to the original black rubber roofing membrane on the Texas retail building studied, a retrofitted vinyl membrane delivered an average decrease of 24 °C (43 °F) in surface temperature, an 11% decrease in aggregate air conditioning energy consumption, and a corresponding 14% drop in peak hour demand.

[54] Another case study, conducted in 2009 and published in 2011, was completed by Ashley-McGraw Architects and CDH Energy Corp for Onondaga County Dept.

[55] In July 2010, the United States Department of Energy announced a series of initiatives to more broadly implement cool roof technologies on DOE facilities and buildings across the country.

Unlike other Energy Star-rated products, such as appliances, this rating system does not look at the entire roof assembly, but only the exterior surface.

This system has been put into an online directory of more than 850 roofing products and is available for energy service providers, building code bodies, architects and specifiers, property owners and community planners.

The basis in physics of a high emittance is quite questionable, since it merely describes a material which easily radiates infrared wavelength heat to the environment, contributing to the greenhouse effect.

[61] Under the LEED 2009 version, to receive Sustainable Sites Credit 7.2 Heat Island Effect-Roof, at least 75% of the surface of a roof must use materials having a solar reflective index (SRI) of at least 78.

In tropical Australia, zinc-galvanized (silvery) sheeting (usually corrugated) do not reflect heat as well as the truly "cool" color of white, especially as metallic surfaces fail to emit infrared back to the sky.

[70] On Wednesday, September 25, 2013 Mayor Michael R Bloomberg declared it "NYC °CoolRoofs Day" in New York City with the coating of its 500th building and reducing the carbon footprint by over 2000 tons.

A study by LBNL showed that, if strategies to mitigate this effect, including cool roofs, were widely adopted, the Greater Toronto metropolitan area could save more than $11 million annually on energy costs.