La Jolla Roofing Contractor and General Contractor Mark Anthony
A cool roof is a roofing system that reflects a significant portion of incoming solar radiation back into the atmosphere while resisting the absorption of solar energy and transfer to the building envelope. The “coolness” of a roof is defined by two properties, solar reflectance and thermal emittance. The properties are measured on a scale from 0 to 1, and the higher the value, the "cooler" the roof. The Solar Reflectance Index (SRI) is a combination of the two properties, and is a common measurement used by manufacturers and building rating systems, such as LEED, to indicate overall performance. For example, to meet the requirements of the LEED credit that addresses the heat-island effect of roofing systems, projects must use roof systems with a SRI of 78 for low-slope roofs (less than or equal to 2:12 slope) or an SRI of 29 for steeply sloped roofs (equal to or greater than 2:12 slope).
Selecting the appropriate roofing can have a significant impact on both the indoor and outdoor environment, as well as the amount of energy required to cool a building. The heat-island effect is a well-known phenomenon that has serious consequences for the quality of life in developed areas. According to research by the Lawrence Berkeley National Laboratories, late afternoon temperatures in cities in the summer months can be from 2 degrees to 10 degrees Fahrenheit higher than in surrounding non-urban areas. This affects comfort levels in the outdoor environment and also greatly increases the heat load that must be managed by building systems. The Department of Energy estimates that using a cool roof would typically result in annual energy savings of 10 to 30 percent, with a significant reduction in operating costs. Of course, the less fossil-fuel energy we use to cool buildings, the fewer greenhouse gas emissions are sent into the atmosphere, slowing the pace of global climate change. Currently, nearly half of the worldwide GHG emissions can be attributed to buildings and their operations.
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