Background
Solar reflectivity is one key factor in the performance of roof, and is especially important in extreme climates. It is the ability for the roof to reflect solar energy rather than absorbing it and transferring heat to the building. It is common knowledge that white is 100% reflective and black is 100% absorbent of solar energy, however roofing isn't as simple as a coat of paint. There are other factors such as thermal emittance, heat capacity, R-value, angle, and material properties that determine how well a roof works. Buildings make up 40% of global energy consumption, and a large portion of that is used to condition our living spaces. Through passive systems and critical thinking about our roof systems it is possible to reduce the amount of energy we use to condition space.
Source: Roofingcontractor.com. 2018. Understanding Cool Roof Technologies.
Literature Review
Solar Reflectivity is the first line of defense (or offense) to passively approach the Sun's relationship with our buildings. Buildings account for about 40% of all Greenhouse Gas emissions, and a significant portion of that is used to condition spaces. HVAC accounts for 20% of all energy consumption in the U.S. and 50% of all energy use in buildings (Pérez-Lombard et al.). It is apparent to us now more than ever that we must try and reduce carbon emissions in order to save the Earth.
In a thesis project done by Preston Haverstic of Arizona State, he determined that the cost of installing and maintaining a solar reflective and solar emissive roof could reduce the cost spent on conditioning a space by 20-30% for the roof's lifetime. While not cost effective for all buildings, some can benefit from this kind of technology. Regardless of personal savings if you include regular maintenance or not, using this roof technology will use 20-30% less energy than a normal roof system over a 20 year period (Haverstic).
There are other factors such as thermal emittance, heat capacity, slope, and material properties that determine how well a roof works, however solar reflectivity is the gatekeeper to the rest of those factors. It controls the amount of energy that's allowed through the roof and into the space. According to a study done by the Civil Engineering Department of Universiti Teknologi PETRONAS in Malaysia, A white roof with no insulation kept an interior space up to 2 ° C cooler than one with a black roof, and reflected more energy than the black roof. Through surveys they discovered that only about 10% of houses in the country actually had a white roof, and most people thought that the maintenance required in order to keep a white roof clean outweighed the amount of money they would save on HVAC. They concluded that in order to become a more environmentally conscious Malaysia it would be necessary to make the white roof desirable not only for it's cost effectiveness but also aesthetically (Al Yacouby et al.).
Building off of aesthetics and building performance, this study by Chiara Ferrari found that there are ways to improve solar reflectivity while still maintaining a similar appearance of traditional roof assemblies. Similar to Malaysia, many Mediterranean cities are characterized by their red ceramic tile roofs. Overall these roofs aren't particularly reflective, however they developed a simple system to maintain the same tiles, with only minor changes to the roof assembly. By changing the color of the tiles to a cooler shade of red, adding a thin insulative layer underneath, a layer of aluminum foil underneath that, and finally using a method to create air pockets between the roof tiles and the roof slab, you can keep a similar aesthetic while improving building performance. Sacrificing some color change they found other ways to increase the reflectivity of the roof. While changing the roof color is still important, there is no need to change the slope of the roof, wall heights, or other traditional features of the style. Not only will this save money in conditioning costs immediately, but is actually cost effective when looking long term (Ferrari et al.).
In a thesis project done by Preston Haverstic of Arizona State, he determined that the cost of installing and maintaining a solar reflective and solar emissive roof could reduce the cost spent on conditioning a space by 20-30% for the roof's lifetime. While not cost effective for all buildings, some can benefit from this kind of technology. Regardless of personal savings if you include regular maintenance or not, using this roof technology will use 20-30% less energy than a normal roof system over a 20 year period (Haverstic).
There are other factors such as thermal emittance, heat capacity, slope, and material properties that determine how well a roof works, however solar reflectivity is the gatekeeper to the rest of those factors. It controls the amount of energy that's allowed through the roof and into the space. According to a study done by the Civil Engineering Department of Universiti Teknologi PETRONAS in Malaysia, A white roof with no insulation kept an interior space up to 2 ° C cooler than one with a black roof, and reflected more energy than the black roof. Through surveys they discovered that only about 10% of houses in the country actually had a white roof, and most people thought that the maintenance required in order to keep a white roof clean outweighed the amount of money they would save on HVAC. They concluded that in order to become a more environmentally conscious Malaysia it would be necessary to make the white roof desirable not only for it's cost effectiveness but also aesthetically (Al Yacouby et al.).
Building off of aesthetics and building performance, this study by Chiara Ferrari found that there are ways to improve solar reflectivity while still maintaining a similar appearance of traditional roof assemblies. Similar to Malaysia, many Mediterranean cities are characterized by their red ceramic tile roofs. Overall these roofs aren't particularly reflective, however they developed a simple system to maintain the same tiles, with only minor changes to the roof assembly. By changing the color of the tiles to a cooler shade of red, adding a thin insulative layer underneath, a layer of aluminum foil underneath that, and finally using a method to create air pockets between the roof tiles and the roof slab, you can keep a similar aesthetic while improving building performance. Sacrificing some color change they found other ways to increase the reflectivity of the roof. While changing the roof color is still important, there is no need to change the slope of the roof, wall heights, or other traditional features of the style. Not only will this save money in conditioning costs immediately, but is actually cost effective when looking long term (Ferrari et al.).
(Ferrari et al.)
Sources
Roofingcontractor.com. 2018. Understanding Cool Roof Technologies. [online] Available at: <https://www.roofingcontractor.com/articles/92802-understanding-cool-roof-technologies> [Accessed 1 March 2021].
Haverstic, P., 2016. [ebook] Arizona State University, pp.1-49. Available at: <https://repository.asu.edu/attachments/176493/content/Haverstic_asu_0010N_16522.pdf> [Accessed 1 March 2021].
Al Yacouby, Ahmad et al. "Study On Roof Tile's Colors In Malaysia For Development Of New Anti-Warming Roof Tiles With Higher Solar Reflectance Index (SRI)". Research Gate, 2011, https://www.researchgate.net/publication/228452587_Study_on_roof_tile's_colors_in_Malaysia_for_development_of_new_anti-warming_roof_tiles_with_higher_Solar_Reflectance_Index_SRI. Accessed 1 Mar 2021.
Pérez-Lombard, Luis et al. "A Review On Buildings Energy Consumption Information". Energy And Buildings, vol 40, no. 3, 2008, pp. 394-398. Elsevier BV, doi:10.1016/j.enbuild.2007.03.007. Accessed 1 Mar 2021.
Ferrari, Chiara et al. "A Composite Cool Colored Tile For Sloped Roofs With High ‘Equivalent’ Solar Reflectance". Energy And Buildings, vol 114, 2016, pp. 221-226. Elsevier BV, doi:10.1016/j.enbuild.2015.06.062. Accessed 1 Mar 2021.
Haverstic, P., 2016. [ebook] Arizona State University, pp.1-49. Available at: <https://repository.asu.edu/attachments/176493/content/Haverstic_asu_0010N_16522.pdf> [Accessed 1 March 2021].
Al Yacouby, Ahmad et al. "Study On Roof Tile's Colors In Malaysia For Development Of New Anti-Warming Roof Tiles With Higher Solar Reflectance Index (SRI)". Research Gate, 2011, https://www.researchgate.net/publication/228452587_Study_on_roof_tile's_colors_in_Malaysia_for_development_of_new_anti-warming_roof_tiles_with_higher_Solar_Reflectance_Index_SRI. Accessed 1 Mar 2021.
Pérez-Lombard, Luis et al. "A Review On Buildings Energy Consumption Information". Energy And Buildings, vol 40, no. 3, 2008, pp. 394-398. Elsevier BV, doi:10.1016/j.enbuild.2007.03.007. Accessed 1 Mar 2021.
Ferrari, Chiara et al. "A Composite Cool Colored Tile For Sloped Roofs With High ‘Equivalent’ Solar Reflectance". Energy And Buildings, vol 114, 2016, pp. 221-226. Elsevier BV, doi:10.1016/j.enbuild.2015.06.062. Accessed 1 Mar 2021.