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Best Practice Guide |
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Commercial Office Buildings |
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Building EnvelopeCool RoofsCool roofs are roofs with special coatings or surfaces that reflect heat. While this seems simple in concept, the cooling benefits can be quite dramatic. Consider that dark surfaces in the sun are up to 70ºF hotter than white ones - this means that when normal rooftop temperatures are peaking at 190ºF during the hot summer months, cool roofs only reach about 120ºF. The ability of your rooftop to reflect solar radiation and reduce surface temperatures is related to how hard cooling equipment needs to work to condition indoor spaces.
Cool roofs make sense when:
Cool roofs are most effective during the hottest part of the day and the hottest time of year, coinciding with peak energy demand. By allowing you to turn down the HVAC - without sacrificing the comfort of employees or tenants - cool roofs reduce energy costs while ensuring that California has reliable energy during the critical summer months. Remember that a cool roof is only one surface, and that any rooftop retrofit should be part of a wider effort to improve insulation of the building envelope. Installing proper levels of insulation provides year round benefits by preventing heat gain in the summer and blocking cold air infiltration in the winter. Most Californian properties will benefit from the savings resulting from cool roofs. However, in a few regions, additional winter heating costs may outweigh summer benefits. This is especially true for mild climates with cool, cloudy summers, like San Francisco. Temperature, Energy and Smog
Cool Roof Calculator
Business ExamplesThe Natural Resources Defense Council applied TOPCOAT MB Plus, a water-based, sprayable liquid membrane coating that has an emissivity rating of 0.95, to their 1917 retrofitted office in Santa Monica. The cool roof reflects nearly 100 percent of solar radiation hitting the rooftop. The cool roof shares real estate with photovoltaic panels, native plants and overhangs that provide shade, further reducing solar heat from radiating into interior spaces. Swinerton, Incorporated, explored dozens of ENERGY STAR-certified roofs for high albedo (i.e., reflectance) and low emissivity (i.e., radiation) to lower indoor temperatures and reduce the urban heat island effect, but none met its high-traffic resistance criteria. Swinerton convinced 3M Company, maker of an elastomeric roofing product, to add a white, high albedo admixture. The resulting experimental product was then tried and tested at 260 Townsend, Swinerton's headquarters in San Francisco. The trial was so successful, 3M is conducting further tests of the new product in order to qualify for ENERGY STAR certification, and hopes to make it available to the building industry. Resources Flex Your Power Product Guide Cool Roofs. Lawrence Berkeley National Laboratory, Heat Island Group, Cool Roof information. U.S. Environmental Protection Agency, Heat Island Reduction Initiative,Cooling Summertime Temperatures: Strategies to Reduce Urban Heat Islands. California Energy Commission, Information on Cool Roof Information. The Cool Roof Rating Council provides accurate radiative property data on roof surfaces. |