Cool Roofs: A Relief to Hot-City Dwellers
A report by an Intergovernmental Panel on climate change shows that the average temperature of the planet will increase by 2 to 7 degrees celsius before the turn of the century. Global warming is not only hazardous for humans, but also damaging for roofs and pavements that cover 60 percent of the earth’s surface and absorb more than 80 percent of the sunlight that shines on them. In occupied properties, the heat results in inflated energy costs, and more frequent roof repairs. This is where cool roofs come in as a possible solution to the problem. In this post, we delve deeper in the subject, covering the benefits of a cool roofing system. But first, time for a terminology update.
Solar Reflectance (SR)
Solar reflectance is the fraction of total sunlight reflected from the surface. Solar Reflectance ranges from about 4 percent for charcoal, to 9 percent for fresh snow. To be considered “cool,” products must have a Solar Reflectance of at least 0.25, and the same applies to cool roofs.
Solar Absorptance (SA)
Solar absorptance is a fraction of the sunlight absorbed by a surface. Surfaces having high solar absorptance get hot in the sun. In opaque surfaces, solar absorptance is: (1 – SR value). Cool roofs have low solar absorptance, which is why they reflect more heat than regular roofs and keep the space cooler during hot days. The solar absorptance is also related to the color of the roof as shown below:
|Solar Absorptance||Typical Color|
|0.475 – 0.7||Medium|
Thermal Emittance (TE)
Thermal Emittance refers to the ability of a roof panel to radiate heat. Roof panels with a high thermal emittance reduce the surface temperature by 30-50 percent, depending upon the color(s) in use, and the property’s location.
- Cool coatings products qualify for tax purpose and can be written off in the year they are installed, unlike traditional roofs that are capitalized over 39 years.
- Cool roofs decrease temperature fluctuations and lengthen the life of roofing equipment and materials. They even increase the efficiency of Solar PV panels
- Cool roofS reduce temperatures in the building by 1 to 2 degree celsius, reducing the use of air conditioners .
- Cool roofs are more comfortable for the places where the roof is used for living spaces and offer thermal comfort improvement
- Creates more reflective paved surfaces and prevent the undesirable glare that are caused by bright roof colors
- Pavements that have lower temperatures are more durable and do not rust easily
- Reduces the need of street lights because of light color that allows better visibility
- Prevents heating of stormwater runoff that can affect metabolism and reproduction of aquatic species
- Encourages comfortable and healthier living by reducing the temperatures of the floor by 2 to 4 degree celsius
- Reduces the number of death caused by subsequent heat waves
- Decreases the demand of electricity that arises from air conditioners in hot areas
- Improves utility capacity utilization, reduce transmission line congestion, and avoid congestion pricing
- Prevents respiratory illness that the World Health Organization predicts to be the third largest reason of increasing deaths
- Reduces net annual cooling energy use by 15 to 20 percent by reflecting almost all the heat energy. The cost saving in energy usage per year in US is $ 735 million with the reduction in CO₂ by 6.2 million tonnes, an amount roughly equal to men emissions in a year.
- Due to the decrease in island heat effect, the quality of air is improved.
- Area of cool roof pavements is relatively easy to measure and monitor with satellite imagery.
Cool roofing saves 10 to 20 percent of the amount spent on energy. If your property needs roof maintenance or a new roofing system, United Renovations can help. Our experts follow a collaborative approach to understand your requirements and help you decide the best roofing systems that give you the maximum returns on your investment. If you have any question about cool roofs or wish to learn more about your options, reach us at (972) 432-6922 for expert consultation or use our contact form.